NIST Special Publication 800-57 Part 1

Revision 4

Recommendation for 

Key Management

Part 1: General

Elaine Barker

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.SP.800-57pt1r4

C O M P U T E R S E C U R I T Y
NIST Special Publication 800-57 Part 1

Revision 4

Recommendation for 

Key Management

Part 1: General

Elaine Barker

Computer Security Division

Information Technology Laboratory

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.SP.800-57pt1r4

January 2016

U.S. Department of Commerce

Penny Pritzker, Secretary

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Director 
Authority

This publication has been developed by NIST in accordance with its statutory responsibilities under 

the Federal Information Security Modernization Act (FISMA) of 2014, 44 U.S.C. § 3541 et seq., 

Public Law (P.L.) 113-283. NIST is responsible for developing information security standards and 

guidelines, including minimum requirements for federal information systems, but such standards 

and guidelines shall not apply to national security systems without the express approval of 

appropriate federal officials exercising policy authority over such systems. This guideline is 

consistent with the requirements of the Office of Management and Budget (OMB) Circular A-130.

Nothing in this publication should be taken to contradict the standards and guidelines made 

mandatory and binding on Federal agencies by the Secretary of Commerce under statutory 

authority. Nor should these guidelines be interpreted as altering or superseding the existing 

authorities of the Secretary of Commerce, Director of the OMB, or any other Federal official. This 

publication may be used by nongovernmental organizations on a voluntary basis and is not subject 

to copyright in the United States. Attribution would, however, be appreciated by NIST. 

National Institute of Standards and Technology Special Publication 800-57 Part 1, 

Revision 4

Natl. Inst. Stand. Technol. Spec. Publ. 800-57 Part 1, Revision 4, 160 pages (January 2016)

CODEN: NSPUE2

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.SP.800-57pt1r4

Certain commercial entities, equipment, or materials may be identified in this document in order to 

describe an experimental procedure or concept adequately. Such identification is not intended to 

imply recommendation or endorsement by NIST, nor is it intended to imply that the entities, 

materials, or equipment are necessarily the best available for the purpose. 

There may be references in this publication to other publications currently under development by 

NIST in accordance with its assigned statutory responsibilities. The information in this publication, 

including concepts and methodologies, may be used by Federal agencies even before the completion 

of such companion publications. Thus, until each publication is completed, current requirements, 

guidelines, and procedures, where they exist, remain operative. For planning and transition purposes, 

Federal agencies may wish to closely follow the development of these new publications by NIST. 

Organizations are encouraged to review all draft publications during public comment periods and 

provide feedback to NIST. Many NIST cybersecurity publications, other than the ones noted above, 

are available at http://csrc.nist.gov/publications.

All comments are subject to release under the Freedom of Information Act (FOIA)

National Institute of Standards and Technology

Attn: Computer Security Division, Information Technology Laboratory

100 Bureau Drive (Mail Stop 8930) Gaithersburg, MD 20899-8930

Email: keymanagement@nist.gov 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

Key Management: General

ii

Reports on Computer Systems Technology

The Information Technology Laboratory (ITL) at the National Institute of Standards and 

Technology (NIST) promotes the U.S. economy and public welfare by providing technical 

leadership for the Nation’s measurement and standards infrastructure. ITL develops tests, 

test methods, reference data, proof of concept implementations, and technical analyses to 

advance the development and productive use of information technology. ITL’s 

responsibilities include the development of management, administrative, technical, and 

physical standards and guidelines for the cost-effective security and privacy of other than 

national security-related information in federal information systems. The Special 

Publication 800-series reports on ITL’s research, guidelines, and outreach efforts in 

information system security, and its collaborative activities with industry, government, and 

academic organizations.

Abstract

This Recommendation provides cryptographic key management guidance. It consists of 

three parts. Part 1 provides general guidance and best practices for the management of 

cryptographic keying material. Part 2 provides guidance on policy and security planning 

requirements for U.S. government agencies. Finally, Part 3 provides guidance when using 

the cryptographic features of current systems. 

Keywords

archive; assurances; authentication; authorization; availability; backup; compromise; 

confidentiality; cryptanalysis; cryptographic key; cryptographic module; digital signature;

hash function; key agreement; key management; key management policy; key recovery; 

key transport; originator-usage period; private key; public key; recipient-usage period; 

secret key; split knowledge; trust anchor.

Acknowledgements

The National Institute of Standards and Technology (NIST) gratefully acknowledges and 

appreciates contributions by previous authors of this document on the many security issues 

associated with this Recommendation: William Barker, William Burr, and Timothy Polk 

from NIST; Miles Smid from Orion Security; and Lydia Zieglar from the National Security 

Agency. NIST also thanks the many contributions by the public and private sectors whose 

thoughtful and constructive comments improved the quality and usefulness of this 

publication.
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

Key Management: General

iii

Executive Summary

The proper management of cryptographic keys is essential to the effective use of 

cryptography for security. Keys are analogous to the combination of a safe. If a safe 

combination is known to an adversary, the strongest safe provides no security against 

penetration. Similarly, poor key management may easily compromise strong algorithms. 

Ultimately, the security of information protected by cryptography directly depends on the 

strength of the keys, the effectiveness of mechanisms and protocols associated with the 

keys, and the protection afforded to the keys. All keys need to be protected against 

modification, and secret and private keys need to be protected against unauthorized 

disclosure. Key management provides the foundation for the secure generation, storage, 

distribution, use and destruction of keys. 

Users and developers are presented with many choices in their use of cryptographic 

mechanisms. Inappropriate choices may result in an illusion of security, but little or no real 

security for the protocol or application. This Recommendation (i.e., Special Publication 

(SP) 800-57) provides background information and establishes frameworks to support 

appropriate decisions when selecting and using cryptographic mechanisms.

This Recommendation does not address the implementation details for cryptographic 

modules that may be used to achieve the security requirements identified. These details are 

addressed in Federal Information Processing Standard (FIPS) 140 [FIPS 140] and its 

associated implementation guidance and derived test requirements (available at 

http://csrc.nist.gov/groups/STM/cmvp/).

This Recommendation is written for several different audiences and is divided into three 

parts:

• Part 1, General, contains basic key management guidance. It is intended to advise 

developers and system administrators on the "best practices" associated with key 

management. Cryptographic module developers may benefit from this general 

guidance by obtaining a greater understanding of the key management features that 

are required to support specific, intended ranges of applications. Protocol 

developers may identify key management characteristics associated with specific 

suites of algorithms and gain a greater understanding of the security services 

provided by those algorithms. System administrators may use this document to 

determine which configuration settings are most appropriate for their information. 

Part 1 of the Recommendation:

1. Defines the security services that may be provided and key types that may be 

employed in using cryptographic mechanisms. 

2. Provides background information regarding the cryptographic algorithms that 

use cryptographic keying material.

3. Classifies the different types of keys and other cryptographic information 

according to their functions, specifies the protection that each type of 

information requires and identifies methods for providing this protection. 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

Key Management: General

iv

4. Identifies the states in which a cryptographic key may exist during its lifetime.

5. Identifies the multitude of functions involved in key management. 

6. Discusses a variety of key management issues related to the keying material. 

Topics discussed include key usage, cryptoperiod length, domain-parameter 

validation, public-key validation, accountability, audit, key management system 

survivability, and guidance for cryptographic algorithm and key size selection. 

• Part 2, General Organization and Management Requirements, is intended primarily 

to address the needs of system owners and managers. It provides a framework and 

general guidance to support establishing cryptographic key management within an 

organization and a basis for satisfying the key management aspects of statutory and 

policy security planning requirements for Federal government organizations. 

• Part 3, Implementation-Specific Key Management Guidance, is intended to address 

the key management issues associated with currently available implementations. 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

Key Management: General

v

Table of Contents

Executive Summary................................................................................................ iii

1 Introduction.......................................................................................................... 1

1.1 Goal/Purpose ...............................................................................................................1

1.2 Audience......................................................................................................................1

1.3 Scope ...........................................................................................................................2

1.4 Purpose of FIPS and NIST Recommendations (NIST Standards)..............................3

1.5 Content and Organization............................................................................................4

2 Glossary of Terms and Acronyms...................................................................... 5

2.1 Glossary.......................................................................................................................5

2.2 Acronyms ..................................................................................................................16

3 Security Services............................................................................................... 18

3.1 Confidentiality...........................................................................................................18

3.2 Data Integrity.............................................................................................................18

3.3 Authentication ...........................................................................................................18

3.4 Authorization.............................................................................................................19

3.5 Non-repudiation.........................................................................................................19

3.6 Support Services........................................................................................................19

3.7 Combining Services...................................................................................................19

4 Cryptographic Algorithms ................................................................................ 22

4.1 Classes of Cryptographic Algorithms .......................................................................22

4.2 Cryptographic Algorithm Functionality....................................................................23

4.2.1 Hash Functions...................................................................................................23

4.2.2 Symmetric-Key Algorithms used for Encryption and Decryption.....................23

4.2.2.1 Advanced Encryption Standard (AES) .......................................................23

4.2.2.2 Triple DEA (TDEA) ...................................................................................24

4.2.2.3 Modes of Operation.....................................................................................24

4.2.3 Message Authentication Codes (MACs)............................................................24

4.2.3.1 MACs Using Block Cipher Algorithms......................................................25

4.2.3.2 MACs Using Hash Functions .....................................................................25

4.2.4 Digital Signature Algorithms.............................................................................25

4.2.5 Key Establishment Schemes ..............................................................................25

4.2.5.1 Discrete-Log Key-Agreement Schemes......................................................26

4.2.5.2 Key Establishment Using Integer-Factorization Schemes..........................26

4.2.5.3 Security Properties of the Key-Establishment Schemes.............................27

4.2.5.4 Key Encryption and Key Wrapping............................................................27

4.2.5.5 Key Confirmation........................................................................................27

4.2.6 Key Establishment Protocols .............................................................................28

4.2.7 Random Bit Generation......................................................................................28
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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5 General Key Management Guidance................................................................ 29

5. 1 Key Types and Other Information.............................................................................29

5.1.1 Cryptographic Keys............................................................................................29

5.1.2 Other Cryptographic or Related Information .....................................................31

5.2 Key Usage .................................................................................................................32

5.3 Cryptoperiods............................................................................................................33

5.3.1 Risk Factors Affecting Cryptoperiods................................................................33

5.3.2 Consequence Factors Affecting Cryptoperiods..................................................34

5.3.3 Other Factors Affecting Cryptoperiods..............................................................34

5.3.3.1 Communications versus Storage.................................................................34

5.3.3.2 Cost of Key Revocation and Replacement .................................................35

5.3.4 Asymmetric Key Usage Periods and Cryptoperiods..........................................35

5.3.5 Symmetric Key Usage Periods and Cryptoperiods............................................36

5.3.6 Cryptoperiod Recommendations for Specific Key Types..................................37

5.3.7 Recommendations for Other Cryptographic or Related Information.................46

5.4 Assurances.................................................................................................................46

5.4.1 Assurance of Integrity (Integrity Protection) .....................................................46

5.4.2 Assurance of Domain Parameter Validity..........................................................46

5.4.3 Assurance of Public-Key Validity......................................................................47

5.4.4 Assurance of Private-Key Possession ................................................................47

5.5 Compromise of Keys and other Keying Material......................................................47

5.6 Guidance for Cryptographic Algorithm and Key-Size Selection..............................51

5.6.1 Comparable Algorithm Strengths.......................................................................51

5.6.2 Defining Appropriate Algorithm Suites.............................................................55

5.6.3 Using Algorithm Suites......................................................................................56

5.6.4 Transitioning to New Algorithms and Key Sizes...............................................57

5.6.5 Security Strength Reduction...............................................................................60

6 Protection Requirements for Cryptographic Information .............................. 62

6.1 Protection and Assurance Requirements...................................................................62

6.1.1 Summary of Protection and Assurance Requirements for Cryptographic Keys63

6.1.2 Summary of Protection Requirements for Other Cryptographic or Related 

Information ......................................................................................................67

6.2 Protection Mechanisms .............................................................................................69

6.2.1 Protection Mechanisms for Cryptographic Information in Transit....................69

6.2.1.1 Availability..................................................................................................69

6.2.1.2 Integrity.......................................................................................................69

6.2.1.3 Confidentiality ............................................................................................70

6.2.1.4 Association with Usage or Application.......................................................71

6.2.1.5 Association with Other Entities ..................................................................71

6.2.1.6 Association with Other Related Information ..............................................71
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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6.2.2 Protection Mechanisms for Information in Storage ...........................................71

6.2.2.1 Availability..................................................................................................72

6.2.2.2 Integrity.......................................................................................................72

6.2.2.3 Confidentiality ...........................................................................................73

6.2.2.4 Association with Usage or Application.......................................................73

6.2.2.5 Association with the Other Entities.............................................................73

6.2.2.6 Association with Other Related Information ..............................................74

6.2.3 Metadata Associated with Cryptographic Information ......................................74

6.2.3.1 Metadata for Keys.......................................................................................74

6.2.3.2 Metadata for Related Cryptographic Information.......................................75

7 Key States and Transitions............................................................................... 76

7.1 Pre-activation State....................................................................................................77

7.2 Active State ...............................................................................................................78

7.3 Suspended State.........................................................................................................80

7.4 Deactivated State .......................................................................................................81

7.5 Compromised State ...................................................................................................82

7.6 Destroyed State..........................................................................................................83

8 Key-Management Phases and Functions ........................................................ 84

8.1 Pre-operational Phase ................................................................................................86

8.1.1 User Registration Function.................................................................................86

8.1.2 System Initialization Function ...........................................................................86

8.1.3 User Initialization Function................................................................................86

8.1.4 Keying-Material Installation Function ...............................................................86

8.1.5 Key Establishment Function ..............................................................................87

8.1.5.1 Generation and Distribution of Asymmetric Key Pairs..............................87

8.1.5.1.1 Distribution of Static Public Keys................................................................. 88

8.1.5.1.1.1 Distribution of a Trust Anchor's Public Key in a PKI........................... 88

8.1.5.1.1.2 Submission to a Registration Authority or Certification Authority....... 90

8.1.5.1.1.3 General Distribution .............................................................................. 92

8.1.5.1.2 Distribution of Ephemeral Public Keys......................................................... 92

8.1.5.1.3 Distribution of Centrally Generated Key Pairs ............................................. 92

8.1.5.2 Generation and Distribution of Symmetric Keys........................................93

8.1.5.2.1 Key Generation ............................................................................................. 93

8.1.5.2.2 Key Distribution............................................................................................ 94

8.1.5.2.2.1 Manual Key Distribution....................................................................... 94

8.1.5.2.2.2 Automated Key Distribution/Key Transport/Key Wrapping ................ 94

8.1.5.2.3 Key Agreement ............................................................................................. 95

8.1.5.3 Generation and Distribution of Other Keying Material ..............................96

8.1.5.3.1 Domain Parameters....................................................................................... 96

8.1.5.3.2 Initialization Vectors..................................................................................... 96
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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8.1.5.3.3 Shared Secrets............................................................................................... 96

8.1.5.3.4 RBG Seeds .................................................................................................... 97

8.1.5.3.5 Other Public and Secret Information............................................................. 97

8.1.5.3.6 Intermediate Results...................................................................................... 97

8.1.5.3.7 Random Bits/Numbers.................................................................................. 97

8.1.5.3.8 Passwords...................................................................................................... 97

8.1.6 Key Registration Function .................................................................................97

8.2 Operational Phase......................................................................................................98

8.2.1 Normal Operational Storage Function ...............................................................99

8.2.1.1 Cryptographic Module Storage...................................................................99

8.2.1.2 Immediately Accessible Storage Media......................................................99

8.2.2 Continuity of Operations Function.....................................................................99

8.2.2.1 Backup Storage ...........................................................................................99

8.2.2.2 Key Recovery Function ............................................................................101

8.2.3 Key Change Function.......................................................................................102

8.2.3.1 Re-keying ..................................................................................................102

8.2.3.2 Key Update Function ................................................................................102

8.2.4 Key Derivation Methods..................................................................................102

8.3 Post-Operational Phase............................................................................................103

8.3.1 Archive Storage and Key Recovery Functions................................................103

8.3.2 Entity De-registration Function........................................................................107

8.3.3 Key De-registration Function...........................................................................107

8.3.4 Key Destruction Function ................................................................................108

8.3.5 Key Revocation Function.................................................................................108

8.4 Destroyed Phase ......................................................................................................109

9 Accountability, Audit, and Survivability ........................................................ 110

9.1 Accountability .........................................................................................................110

9.2 Audit........................................................................................................................110

9.3 Key Management System Survivability..................................................................111

9.3.1 Backup Keys ....................................................................................................111

9.3.2 Key Recovery...................................................................................................111

9.3.3 System Redundancy/Contingency Planning ....................................................112

9.3.3.1 General Principles.....................................................................................112

9.3.3.2 Cryptography and Key Management-specific Recovery Issues ...............113

9.3.4 Compromise Recovery.....................................................................................113

10 Key Management Specifications for Cryptographic Devices or Applications

.................................................................................................................. 115

10.1 Key Management Specification Description/Purpose.............................................115

10.2 Content of the Key Management Specification.......................................................115
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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10.2.1 Cryptographic Application...............................................................................116

10.2.2 Communications Environment.........................................................................116

10.2.3 Key Management Component Requirements ..................................................116

10.2.4 Key Management Component Generation.......................................................117

10.2.5 Key Management Component Distribution .....................................................117

10.2.6 Keying Material Storage ..................................................................................117

10.2.7 Access Control .................................................................................................117

10.2.8 Accounting .......................................................................................................117

10.2.9 Compromise Management and Recovery ........................................................118

10.2.10 Key Recovery..................................................................................................118

APPENDIX A: Cryptographic and Non-cryptographic Integrity and Source 

Authentication Mechanisms .................................................................. 119

APPENDIX B: Key Recovery ............................................................................... 122

B.1 Recovery from Stored Keying Material ..................................................................123

B.2 Recovery by Reconstruction of Keying Material....................................................123

B.3 Conditions Under Which Keying Material Needs to be Recoverable.....................123

B.3.1 Signature Key Pairs..........................................................................................123

B.3.1.1 Private Signature Keys..............................................................................124

B.3.1.2 Public Signature-verification Keys...........................................................124

B.3.2 Symmetric Authentication Keys ......................................................................124

B.3.3 Authentication Key Pairs .................................................................................125

B.3.3.1 Public Authentication Keys ......................................................................125

B.3.3.2 Private Authentication Keys .....................................................................126

B.3.4 Symmetric Data-Encryption Keys ...................................................................126

B.3.5 Symmetric Key-Wrapping Keys......................................................................126

B.3.6 Random Number Generation Keys..................................................................127

B.3.7 Symmetric Master Keys...................................................................................127

B.3.8 Key-Transport Key Pairs..................................................................................127

B.3.8.1 Private Key-Transport Keys......................................................................127

B.3.8.2 Public Key Transport Keys.......................................................................127

B.3.9 Symmetric Key Agreement Keys.....................................................................128

B.3.10 Static Key-Agreement Key Pairs .....................................................................128

B.3.10.1 Private Static Key-Agreement Keys .........................................................128

B.3.10.2 Public Static Key Agreement Keys...........................................................128

B.3.11 Ephemeral Key Pairs........................................................................................129

B.3.11.1 Private Ephemeral Keys.......................................................................129

B.3.11.2 Public Ephemeral Keys.............................................................................129

B.3.12 Symmetric Authorization Keys........................................................................129

B.3.13 Authorization Key Pairs...................................................................................129

B.3.13.1 Private Authorization Keys.......................................................................129
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B.3.13.2 Public Authorization Keys........................................................................130

B.3.14 Other Cryptographically Related Material.......................................................130

B.3.14.1 Domain Parameters...................................................................................130

B.3.14.2 Initialization Vectors (IVs) .......................................................................130

B.3.14.3 Shared Secrets...........................................................................................130

B.3.14.4 RBG Seeds................................................................................................130

B.3.14.5 Other Public and Secret Information.........................................................131

B.3.14.6 Intermediate Results..................................................................................131

B.3.14.7 Key Control Information...........................................................................131

B.3.14.8 Random Numbers .....................................................................................131

B.3.14.9 Passwords..................................................................................................131

B.3.14.10 Audit Information.................................................................................131

B.4 Key Recovery Systems............................................................................................131

B.5 Key Recovery Policy...............................................................................................133

APPENDIX C: References ................................................................................... 135

APPENDIX D: Revisions...................................................................................... 140

List of Tables

Table 1: Suggested cryptoperiods for key types......................................................................45

Table 2: Comparable strengths ................................................................................................53

Table 3: Hash functions that can be used to provide the targeted security strengths ..............54

Table 4: Security-strength time frames....................................................................................55

Table 5: Protection requirements for cryptographic keys........................................................64

Table 6: Protection requirements for other cryptographic or related material.........................67

Table 7: Backup of keys ........................................................................................................100

Table 8: Backup of other cryptographic or related information ............................................101

Table 9: Archive of keys........................................................................................................105

Table 10: Archive of other cryptographic related information..............................................106
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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List of Figures

Figure 1: Symmetric key cryptoperiod ....................................................................................37

Figure 2: Algorithm Originator-Usage Period Example..........................................................59

Figure 3: Key state and transition example..............................................................................76

Figure 4: Key management phases. .........................................................................................84

Figure 5: Key management states and phases..........................................................................85
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

Key Management: General

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1 Introduction

The use of cryptographic mechanisms is one of the strongest ways to provide security services 

for electronic applications and protocols and for data storage. The National Institute of 

Standards and Technology (NIST) publishes Federal Information Processing Standards (FIPS) 

and NIST Recommendations (which are published as Special Publications) that specify 

cryptographic techniques for protecting sensitive, unclassified information.

Since NIST published the Data Encryption Standard (DES) in 1977, the suite of approved

standardized algorithms has been growing. New classes of algorithms have been added, such 

as secure hash functions and asymmetric key algorithms for digital signatures. The suite of 

algorithms now provides different levels of cryptographic strength through a variety of key 

sizes. The algorithms may be combined in many ways to support increasingly complex 

protocols and applications. This NIST Recommendation applies to U.S. government agencies 

using cryptography for the protection of their sensitive, unclassified information. This 

Recommendation may also be followed, on a voluntary basis, by other organizations that want 

to implement sound security principles in their computer systems. 

The proper management of cryptographic keys is essential to the effective use of cryptography 

for security. Keys are analogous to the combination of a safe. If an adversary knows the 

combination, the strongest safe provides no security against penetration. Similarly, poor key 

management may easily compromise strong algorithms. Ultimately, the security of information 

protected by cryptography directly depends on the strength of the keys, the effectiveness of the 

mechanisms and protocols associated with the keys, and the protection afforded the keys. 

Cryptography can be rendered ineffective by the use of weak products, inappropriate algorithm 

pairing, poor physical security, and the use of weak protocols. 

All keys need to be protected against unauthorized substitution and modification. Secret and 

private keys need to be protected against unauthorized disclosure. Key management provides 

the foundation for the secure generation, storage, distribution, and destruction of keys. 

1.1 Goal/Purpose

Users and developers are presented with many new choices in their use of cryptographic 

mechanisms. Inappropriate choices may result in an illusion of security, but little or no real 

security for the protocol or application. This Recommendation (i.e., SP 800-57) provides 

background information and establishes frameworks to support appropriate decisions when 

selecting and using cryptographic mechanisms.

1.2 Audience

The audiences for this Recommendation for Key Management include system or application 

owners and managers, cryptographic module developers, protocol developers, and system 

administrators. The Recommendation has been provided in three parts. The different parts into 

which the Recommendation has been divided have been tailored to specific audiences. 

Part 1 of this Recommendation provides general key management guidance that is intended to 

be useful to both system developers and system administrators. Cryptographic module 

developers may benefit from this general guidance through a greater understanding of the key 

management features that are required to support specific intended ranges of applications. 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

Key Management: General

2

Protocol developers may identify key management characteristics associated with specific 

suites of algorithms and gain a greater understanding of the security services provided by those 

algorithms. System administrators may use this Recommendation to determine which 

configuration settings are most appropriate for their information. 

Part 2 of this Recommendation [SP800-57, Part 2] is tailored for system or application owners 

for use in identifying appropriate organizational key management infrastructures, establishing 

organizational key management policies, and specifying organizational key management 

practices and plans. 

Part 3 of this Recommendation addresses the key management issues associated with currently

available cryptographic mechanisms and is intended to provide guidance to system installers, 

system administrators and end users of existing key management infrastructures, protocols, and 

other applications, as well as the people making purchasing decisions for new systems using 

currently available technology.

Although some background information and rationale are provided for context and to support 

the recommendations, this document assumes that the reader has a basic understanding of 

cryptography. For background material, readers may look to a variety of NIST and commercial 

publications, including [SP800-32], which provides an introduction to a public-key 

infrastructure. 

1.3 Scope

This Recommendation encompasses cryptographic algorithms, infrastructures, protocols, and 

applications, and the management thereof. All cryptographic algorithms currently approved by 

NIST for the protection of unclassified, but sensitive information are in scope. 

This Recommendation focuses on issues involving the management of cryptographic keys: 

their generation, use, and eventual destruction. Related topics, such as algorithm selection and 

appropriate key size, cryptographic policy, and cryptographic module selection, are also 

included in this Recommendation. Some of the topics noted above are addressed in other NIST 

standards and guidance. This Recommendation supplements more-focused standards and 

guidelines. 

This Recommendation does not address the implementation details for cryptographic modules 

that may be used to achieve the security requirements identified. These details are addressed in 

[FIPS140], the FIPS 140 implementation guidance and the derived test requirements (available 

at http://csrc.nist.gov/ groups/STM/cmvp/standards.html). 

This Recommendation also does not address the requirements or procedures for operating an 

archive, other than discussing the types of keying material that are appropriate to include in an 

archive and the protection to be provided to the archived keying material. 

This Recommendation often uses “requirement” terms; these terms have the following 

meaning in this document:

1. shall: This term is used to indicate a requirement of a Federal Information Processing 

Standard (FIPS) or a requirement that must be fulfilled to claim conformance to this 

Recommendation. Note that shall may be coupled with not to become shall not. 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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2. should: This term is used to indicate an important recommendation. Ignoring the 

recommendation could result in undesirable results. Note that should may be coupled 

with not to become should not. 

1.4 Purpose of FIPS and NIST Recommendations (NIST Standards)

Federal Information Processing Standards (FIPS) and NIST Recommendations, collectively 

referred to as "NIST standards," are valuable because:

1. They establish an acceptable minimal level of security for U.S. government systems. 

Systems that implement these NIST standards offer a consistent level of security 

approved for the protection of sensitive, unclassified government data.

2. They often establish some level of interoperability between different systems that 

implement the NIST standard. For example, two products that both implement the 

Advanced Encryption Standard (AES) cryptographic algorithm have the potential to 

interoperate, provided that the other functions of the product are compatible.

3. They often provide for scalability, because the U.S. government requires products and 

techniques that can be effectively applied in large numbers.

4. They are scrutinized by U.S. government experts and the public to ensure that they 

provide a high level of security. The NIST standards process invites broad public 

participation, not only through the formal NIST public review process before adoption, 

but also by interaction with the open cryptographic community through NIST 

workshops, participation in voluntary standards development organizations, 

participation in cryptographic research conferences and informal contacts with 

researchers. NIST encourages study and cryptanalysis of NIST standards, and inputs 

on their security are welcome at any point, from initial requirements, during 

development and after adoption.

5. NIST-approved cryptographic techniques are periodically re-assessed for their 

continued effectiveness. If any technique is found to be inadequate for the continued 

protection of government information, the NIST standard is revised or discontinued.

6. The algorithms specified in NIST standards (e.g., AES, TDEA, SHA-2, and DSA) and 

the cryptographic modules in which they reside have required conformance tests. 

Accredited laboratories perform these tests on vendor implementations that claim 

conformance to the standards. Vendors are permitted to modify non-conforming 

implementations so that they meet all applicable requirements. Users of validated 

implementations can have a high degree of confidence that validated implementations

conform to the standards.

Since 1977, NIST has developed a cryptographic “toolkit” of NIST standards1 that form a 

basis for the implementation of approved cryptography. This Recommendation references 

many of those standards, and provides guidance on how they may be properly used to protect 

sensitive information.

 

1 The toolkit consists of publications specifying algorithms and guidance for their use, rather than software code.
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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1.5 Content and Organization

Part 1, General Guidance, contains basic key management guidance. It is intended to advise 

developers and system administrators on the "best practices" associated with key management.

• Section 1, Introduction, establishes the purpose, scope and intended audience of the 

Recommendation for Key Management

• Section 2, Glossary of Terms and Acronyms, provides definitions of terms and 

acronyms used in this part of the Recommendation for Key Management. The reader 

should be aware that the terms used in this Recommendation might be defined 

differently in other documents.

• Section 3, Security Services, defines the security services that may be provided using 

cryptographic mechanisms. 

• Section 4, Cryptographic Algorithms, provides background information regarding the 

cryptographic algorithms that use cryptographic keying material.

• Section 5, General Key Management Guidance, classifies the different types of keys 

and other cryptographic information according to their uses, discusses cryptoperiods 

and recommends appropriate cryptoperiods for each key type, provides 

recommendations and requirements for other keying material, introduces assurance of 

domain-parameter and public-key validity, discusses the implications of the 

compromise of keying material, and provides guidance on cryptographic algorithm 

strength selection implementation and replacement.

• Section 6, Protection Requirements for Cryptographic Information, specifies the 

protection that each type of information requires and identifies methods for providing 

this protection. These protection requirements are of particular interest to cryptographic 

module vendors and application implementers.

• Section 7, Key State and Transitions, identifies the states in which a cryptographic key 

may exist during its lifetime.

• Section 8, Key Management Phases and Functions, identifies four phases and a 

multitude of functions involved in key management. This section is of particular 

interest to cryptographic module vendors and developers of cryptographic 

infrastructure services.

• Section 9, Accountability, Audit, and Survivability, discusses three control principles 

that are used to protect the keying material identified in Section 5.1. 

• Section 10, Key Management Specifications for Cryptographic Devices or 

Applications, specifies the content and requirements for key management

specifications. Topics covered include the communications environment, component 

requirements, keying material storage, access control, accounting, and compromise 

recovery.

Appendices A and B are provided to supplement the main text where a topic demands a more 

detailed treatment. Appendix C contains a list of appropriate references, and Appendix D

contains a list of changes since the originally published version of this document.
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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2 Glossary of Terms and Acronyms

The definitions provided below are defined as used in this document. The same terms may be 

defined differently in other documents.

2.1 Glossary

Access control Restricts resource access to only privileged entities.

Accountability A property that ensures that the actions of an entity may be traced 

uniquely to that entity.

Algorithm originatorusage periodThe period of time during which a specific cryptographic algorithm 

may be used by originators to apply protection to data (e.g., encrypt or 

generate a digital signature).

Algorithm security 

lifetime

The estimated time period during which data protected by a specific 

cryptographic algorithm remains secure.

Approved FIPS-approved and/or NIST-recommended. An algorithm or 

technique that is either 1) specified in a FIPS or NIST 

Recommendation, or 2) specified elsewhere and adopted by reference 

in a FIPS or NIST Recommendation.

Archive 1. To place information into long-term storage. 

2. A location or media used for long-term storage. 

Association A relationship for a particular purpose. For example, a key is 

associated with the application or process for which it will be used.

Assurance of (private 

key) possession

Confidence that an entity possesses a private key and its associated 

keying material.

Assurance of validity Confidence that a public key or domain parameter is arithmetically 

correct.

Asymmetric key 

algorithm

See Public-key cryptographic algorithm.

Authentication A process that provides assurance of the source and integrity of 

information in communications sessions, messages, documents or 

stored data.

Authentication code A keyed cryptographic checksum based on an approved security 

function (also known as a Message Authentication Code).

Authorization Access privileges that are granted to an entity; conveying an “official” 

sanction to perform a security function or activity.

Availability Timely, reliable access to information by authorized entities.
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Backup A copy of information to facilitate recovery during the cryptoperiod of 

the key, if necessary.

Certificate See Public-key certificate.

Certification authority The entity in a Public Key Infrastructure (PKI) that issues certificates 

to certificate subjects.

Ciphertext Data in its encrypted form.

Collision Two or more distinct inputs produce the same output. Also see Hash 

function.

Compromise The unauthorized disclosure, modification, substitution or use of 

sensitive data (e.g., keying material and other security-related 

information).

Confidentiality The property that sensitive information is not disclosed to unauthorized 

entities.

Contingency plan A plan that is maintained for disaster response, backup operations, and 

post-disaster recovery to ensure the availability of critical resources 

and to facilitate the continuity of operations in an emergency situation.

Contingency planning The development of a contingency plan.

Cryptanalysis 1. Operations performed to defeat cryptographic protection without an 

initial knowledge of the key employed in providing the protection. 

2. The study of mathematical techniques for attempting to defeat 

cryptographic techniques and information system security. This 

includes the process of looking for errors or weaknesses in the 

implementation of an algorithm or in the algorithm itself.

Cryptographic 

algorithm

A well-defined computational procedure that takes variable inputs,

including a cryptographic key, and produces an output.

Cryptographic 

boundary

An explicitly defined continuous perimeter that establishes the physical 

bounds of a cryptographic module and contains all hardware, software, 

and/or firmware components of a cryptographic module.

Cryptographic hash 

function

See Hash function.
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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Cryptographic key 

(key)

A parameter used in conjunction with a cryptographic algorithm that 

determines its operation in such a way that an entity with knowledge of 

the key can reproduce, reverse or verify the operation, while an entity 

without knowledge of the key cannot. Examples include:

1. The transformation of plaintext data into ciphertext data,

2. The transformation of ciphertext data into plaintext data,

3. The computation of a digital signature from data,

4. The verification of a digital signature on data,

5. The computation of an authentication code from data, 

6. The verification of an authentication code from data and a 

received authentication code,

7. The computation of a shared secret that is used to derive keying 

material.

Cryptographic key 

component (key 

component)

One of at least two parameters that have the same security properties 

(e.g., randomness) as a cryptographic key; parameters are combined in 

an approved security function to form a plaintext cryptographic key 

before use.

Cryptographic module The set of hardware, software, and/or firmware that implements 

approved security functions (including cryptographic algorithms and 

key generation) and is contained within a cryptographic boundary.

Cryptoperiod The time span during which a specific key is authorized for use or in 

which the keys for a given system or application may remain in effect.

Data-encryption key A key used to encrypt and decrypt information other than keys.

Data integrity A property whereby data has not been altered in an unauthorized 

manner since it was created, transmitted or stored. 

Decryption The process of changing ciphertext into plaintext using a cryptographic 

algorithm and key.

Deterministic random 

bit generator (DRBG)

A random bit generator that includes a DRBG algorithm and (at least 

initially) has access to a source of randomness. The DRBG produces a 

sequence of bits from a secret initial value called a seed, along with 

other possible inputs. A cryptographic DRBG has the additional 

property that the output is unpredictable, given that the seed is not 

known. A DRBG is sometimes also called a Pseudo-random Number 

Generator (PRNG) or a deterministic random number generator. 
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Digital signature The result of a cryptographic transformation of data that, when 

properly implemented with a supporting infrastructure and policy, 

provides the services of:

1. Origin (i.e., source) authentication,

2. Data integrity authentication, and

3. Support for signer non-repudiation.

Distribution See Key distribution.

Domain parameter A parameter used in conjunction with some public-key algorithms to 

generate key pairs, to create digital signatures, or to establish keying 

material.

Encrypted key A cryptographic key that has been encrypted using an approved

security function in order to disguise the value of the underlying 

plaintext key.

Encryption The process of changing plaintext into ciphertext using a cryptographic 

algorithm and key.

Entity An individual (person), organization, device or process.

Ephemeral key A cryptographic key that is generated for each execution of a keyestablishment process and that meets other requirements of the key 

type (e.g., unique to each message or session).

In some cases, ephemeral keys are used more than once within a single 

session (e.g., for broadcast applications) where the sender generates 

only one ephemeral key pair per message, and the private key is 

combined separately with each recipient’s public key.

Hash-based message 

authentication code 

(HMAC)

A message authentication code that uses an approved keyed-hash 

function (i.e., [FIPS 198]).

Hash function A function that maps a bit string of arbitrary (although bounded) length 

to a fixed-length bit string. Approved hash functions satisfy the 

following properties:

1. (One-way) It is computationally infeasible to find any input that 

maps to any pre-specified output, and

2. (Collision resistant) It is computationally infeasible to find any 

two distinct inputs that map to the same output.

Hash value The result of applying a hash function to information.
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Identifier A bit string that is associated with a person, device or organization. It 

may be an identifying name, or may be something more abstract (for 

example, a string consisting of an IP address and timestamp),

depending on the application.

Identity The distinguishing character or personality of an entity.

Initialization vector 

(IV)

A vector used in defining the starting point of a cryptographic process. 

Integrity (also,

Assurance of integrity)

See Data integrity.

Integrity 

authentication

The process of providing assurance that data has not been modified 

since an authentication code was created for that data.

Integrity protection See Integrity authentication.

Key See Cryptographic key.

Key agreement A key-establishment procedure where resultant keying material is a 

function of information contributed by two or more participants, so 

that no party can predetermine the value of the keying material 

independently of any other party’s contribution.

Key component See Cryptographic key component. 

Key confirmation A procedure used to provide assurance to one party that another party 

actually possesses the same keying material and/or shared secret.

Key de-registration A function in the lifecycle of keying material; the marking of all 

keying material records and associations to indicate that the key is no 

longer in use.

Key derivation The process by which one or more keys are derived from either a preshared key or a shared secret (from a key-agreement scheme), along 

with other information.

Key-derivation 

function

A function that, with the input of a cryptographic key or shared secret,

and possibly other data, generates a binary string, called keying 

material.

Key-derivation key A key used with a key-derivation function or method to derive 

additional keys. Sometimes called a master key.

Key-derivation 

method

A key-derivation function or other approved procedure for deriving 

keying material. 

Key destruction To remove all traces of keying material so that it cannot be recovered 

by either physical or electronic means.
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Key distribution The transport of a key and other keying material from an entity that

either owns or generates the key to another entity that is intended to 

use the key.

Key-encrypting key A cryptographic key that is used for the encryption or decryption of 

other keys to provide confidentiality protection. Also see Keywrapping key.

Key establishment A function in the lifecycle of keying material; the process by which 

cryptographic keys are securely established among cryptographic 

modules using manual transport methods (e.g., key loaders), automated 

methods (e.g., key-transport and/or key-agreement protocols), or a 

combination of automated and manual methods.

Key length The length of a key in bits; used interchangeably with “Key size”.

Key management The activities involving the handling of cryptographic keys and other 

related security parameters (e.g., initialization vectors) during the 

entire lifecycle of the keys, including their generation, storage, 

establishment, entry and output, use and destruction.

Key Management 

Policy

A high-level statement of organizational key management policies that 

identifies a high-level structure, responsibilities, governing standards, 

organizational dependencies and other relationships, and security 

policies.

Key Management 

Practices Statement

A document or set of documents that describes, in detail, the 

organizational structure, responsible roles, and organization rules for 

the functions identified in the Key Management Policy.

Key pair A public key and its corresponding private key; a key pair is used with 

a public-key algorithm.

Key recovery A function in the lifecycle of keying material; mechanisms and 

processes that allow authorized entities to retrieve or reconstruct 

keying material from key backup or archive.

Key registration A function in the lifecycle of keying material; the process of officially 

recording the keying material by a registration authority.

Key revocation A function in the lifecycle of keying material; a process whereby a 

notice is made available to affected entities that keying material should

be removed from operational use prior to the end of the established 

cryptoperiod of that keying material. 

Key size The length of a key in bits; used interchangeably with “Key length”.
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Key transport A key-establishment procedure whereby one party (the sender) selects 

and encrypts (or wraps) the keying material and then distributes the 

material to another party (the receiver). 

When used in conjunction with a public-key (asymmetric) algorithm, 

the keying material is encrypted using the public key of the receiver 

and subsequently decrypted using the private key of the receiver. 

When used in conjunction with a symmetric algorithm, the keying 

material is encrypted with a key-wrapping key shared by the two 

parties. 

Key update A function performed on a cryptographic key in order to compute a 

new key that is related to the old key.

Key wrapping A method of cryptographically protecting keys using a symmetric key 

that provides both confidentiality and integrity protection.

Key-wrapping key A symmetric key-encrypting key that is used to provide both 

confidentiality and integrity protection. Also see Key-encrypting key.

Keying material The data (e.g., keys and IVs) necessary to establish and maintain 

cryptographic keying relationships.

Manual key transport A non-automated means of transporting cryptographic keys by 

physically moving a device or document containing the key or key 

component.

Master key See Key-derivation key.

Message 

authentication code 

(MAC)

A cryptographic checksum on data that uses an approved security 

function and a symmetric key to detect both accidental and intentional 

modifications of data. 

Metadata Information used to describe specific characteristics, constraints, 

acceptable uses and parameters of another data item (e.g., a 

cryptographic key).

NIST standards Federal Information Processing Standards (FIPS) and NIST 

Recommendations.

Non-repudiation A service using a digital signature that is used to support a 

determination of whether a message was actually signed by a given 

entity.

Operational phase A phase in the lifecycle of keying material whereby keying material is 

used for standard cryptographic purposes.

Operational storage The normal storage of operational keying material during its 

cryptoperiod.
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Owner For a static key pair, the entity that is associated with the public key 

and authorized to use the private key. For an ephemeral key pair, the 

owner is the entity that generated the public/private key pair. For a 

symmetric key, the owner is any entity that is authorized to use the 

key. 

Originator-usage 

period

The period of time in the cryptoperiod of a key during which 

cryptographic protection may be applied to data using that key.

Password A string of characters (letters, numbers and other symbols) that are 

used to authenticate an identity, to verify access authorization or to 

derive cryptographic keys.

Period of protection The period of time during which the integrity and/or confidentiality of 

a key needs to be maintained.

Plaintext Intelligible data that has meaning and can be understood without the 

application of decryption.

Private key A cryptographic key, used with a public-key cryptographic algorithm 

that is uniquely associated with an entity and is not made public. In an 

asymmetric (public) cryptosystem, the private key has a corresponding

public key. Depending on the algorithm, the private key may be used, 

for example, to:

1. Compute the corresponding public key,

2. Compute a digital signature that may be verified by the 

corresponding public key,

3. Decrypt keys that were encrypted by the corresponding public 

key, or

4. Compute a shared secret during a key-agreement transaction.

Proof of possession 

(POP)

A verification process whereby assurance is obtained that the owner of 

a key pair actually has the private key associated with the public key. 

Pseudorandom 

number generator 

(PRNG)

See Deterministic random bit generator (DRBG).
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Public key A cryptographic key, used with a public-key cryptographic algorithm,

that is uniquely associated with an entity and that may be made public. 

In an asymmetric (public) cryptosystem, the public key has a

corresponding private key. The public key may be known by anyone 

and, depending on the algorithm, may be used, for example, to:

1. Verify a digital signature that is signed by the corresponding 

private key,

2. Encrypt keys that can be decrypted using the corresponding 

private key, or

3. Compute a shared secret during a key-agreement transaction. 

Public-key certificate A set of data that uniquely identifies an entity, contains the entity's 

public key and possibly other information, and is digitally signed by a 

trusted party, thereby binding the public key to the entity. Additional 

information in the certificate could specify how the key is used and its 

validity period.

Public-key 

(asymmetric) 

cryptographic 

algorithm

A cryptographic algorithm that uses two related keys: a public key and 

a private key. The two keys have the property that determining the 

private key from the public key is computationally infeasible.

Public Key 

Infrastructure (PKI)

A framework that is established to issue, maintain and revoke publickey certificates.

Random bit generator 

(RBG)

A device or algorithm that outputs a sequence of bits that appears to be 

statistically independent and unbiased. Also, see Random number 

generator.

Random number 

generator (RNG)

A process used to generate an unpredictable series of numbers. Also 

called a Random bit generator (RBG).

Recipient-usage 

period

The period of time during which the protected information is processed

(e.g., decrypted). 

Registration authority A trusted entity that establishes and vouches for the identity of a user.

Retention period The minimum amount of time that a key or other cryptographically

related information should be retained in an archive.

RBG seed A string of bits that is used to initialize a DRBG. Also just called a 

Seed.
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Secret key A cryptographic key that is used with a secret-key (symmetric) 

cryptographic algorithm that is uniquely associated with one or more 

entities and is not made public. The use of the term “secret” in this 

context does not imply a classification level, but rather implies the 

need to protect the key from disclosure.

Secure communication 

protocol

A communication protocol that provides the appropriate 

confidentiality, source authentication, and data integrity protection.

Security domain A system or subsystem that is under the authority of a single trusted 

authority. Security domains may be organized (e.g., hierarchically) to 

form larger domains.

Security life of data The time period during which the security of the data needs to be 

protected (e.g., its confidentiality, integrity or availability). 

Security services Mechanisms used to provide confidentiality, integrity authentication, 

source authentication and/or support non-repudiation of information.

Security strength

(Also “bits of 

security”)

A number associated with the amount of work (that is, the number of 

operations) that is required to break a cryptographic algorithm or 

system. In this Recommendation, the security strength is specified in 

bits and is a specific value from the set {80, 112, 128, 192, 256}. Note 

that a security strength of 80 bits is no longer considered sufficiently 

secure.

Seed A secret value that is used to initialize a process (e.g., a DRBG). Also 

see RBG seed.

Self-signed certificate A public-key certificate whose digital signature may be verified by the 

public key contained within the certificate. The signature on a selfsigned certificate protects the integrity of the data, but does not 

guarantee the authenticity of the information. The trust of self-signed 

certificates is based on the secure procedures used to distribute them.

Shall This term is used to indicate a requirement of a Federal Information 

Processing Standard (FIPS) or a requirement that must be fulfilled to 

claim conformance to this Recommendation. Note that shall may be 

coupled with not to become shall not.

Shared secret A secret value that has been computed using a key-agreement scheme 

and is used as input to a key-derivation function/method.

Should This term is used to indicate a very important recommendation. 

Ignoring the recommendation could result in undesirable results. Note 

that should may be coupled with not to become should not.

Signature generation The use of a digital signature algorithm and a private key to generate a 

digital signature on data.
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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Signature verification The use of a digital signature algorithm and a public key to verify a 

digital signature on data.

Source authentication The process of providing assurance about the source of information.

Sometimes called identity authentication or origin authentication.

Split knowledge A process by which a cryptographic key is split into n key components, 

each of which provides no knowledge of the original key. The 

components can be subsequently combined to recreate the original 

cryptographic key. If knowledge of k (where k is less than or equal to 

n) components is required to construct the original key, then 

knowledge of any k – 1 key components provides no information about 

the original key other than, possibly, its length.

Note that in this Recommendation, split knowledge is not intended to 

cover key shares, such as those used in threshold or multi-party 

signatures.

Static key A key that is intended for use for a relatively long period of time and is 

typically intended for use in many instances of a cryptographic keyestablishment scheme. Contrast with an Ephemeral key.

Symmetric key A single cryptographic key that is used with a secret (symmetric) key 

algorithm.

Symmetric-key 

algorithm

A cryptographic algorithm that uses the same secret key for an 

operation and its complement (e.g., encryption and decryption). 

System initialization A function in the lifecycle of keying material; setting up and 

configuring a system for secure operation.

Trust anchor 1. An authoritative entity for which trust is assumed. In a PKI, a trust 

anchor is a certification authority, which is represented by a certificate 

that is used to verify the signature on a certificate issued by that trustanchor. The security of the validation process depends upon the 

authenticity and integrity of the trust anchor's certificate. Trust anchor

certificates are often distributed as self-signed certificates. 

2. The self-signed public key certificate of a trusted CA. 

Unauthorized 

disclosure

An event involving the exposure of information to entities not 

authorized access to the information.

User See Entity.

User initialization A function in the lifecycle of keying material; the process whereby a 

user initializes its cryptographic application (e.g., installing and 

initializing software and hardware).
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User registration A function in the lifecycle of keying material; a process whereby an 

entity becomes a member of a security domain.

X.509 certificate The X.509 public-key certificate or the X.509 attribute certificate, as

defined by the ISO/ITU-T X.509 standard. Most commonly (including 

in this document), an X.509 certificate refers to the X.509 public-key 

certificate.

X.509 public-key 

certificate

A digital certificate containing a public key for an entity and a name 

for that entity, together with some other information that is rendered 

un-forgeable by the digital signature of the certification authority that 

issued the certificate, encoded in the format defined in the ISO/ITU-T 

X.509 standard.

2.2 Acronyms

The following abbreviations and acronyms are used in this Recommendation:

2TDEA Two-key Triple Data Encryption Algorithm specified in [SP800-67].

3TDEA Three-key Triple Data Encryption Algorithm specified in [SP800-67].

AES Advanced Encryption Standard specified in [FIPS197].

ANS American National Standard.

ANSI American National Standards Institute.

CA Certification Authority.

CRC Cyclic Redundancy Check.

CRL Certificate Revocation List.

DRBG Deterministic Random Bit Generator.

DSA Digital Signature Algorithm specified in [FIPS186].

ECC Elliptic Curve Cryptography.

ECDSA Elliptic Curve Digital Signature Algorithm specified in [ANSX9.62] and 

approved in [FIPS186].

FFC Finite Field Cryptography.

FIPS Federal Information Processing Standard.

HMAC Keyed-Hash Message Authentication Code specified in [FIPS198].

IFC Integer Factorization Cryptography.

IV Initialization Vector.

MAC Message Authentication Code.

NIST National Institute of Standards and Technology.

PKI Public-Key Infrastructure.
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POP Proof of Possession.

RA Registration Authority.

RBG Random Bit Generator.

RNG Random Number Generator.

RSA Rivest, Shamir, Adelman; an algorithm approved in [FIPS186] for digital 

signatures and in [SP800-56B] for key establishment.

S/MIME Secure Multipurpose Internet Mail Extensions.

TDEA Triple Data Encryption Algorithm; Triple DEA specified in [SP800-67].

TLS Transport Layer Security
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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3 Security Services

Cryptography may be used to perform or support several basic security services: 

confidentiality, integrity authentication, source authentication, authorization and nonrepudiation. These services may also be required to protect cryptographic keying material. In 

addition, there are other cryptographic and non-cryptographic mechanisms that are used to 

support these security services. In general, a single cryptographic mechanism may provide 

more than one service (e.g., the use of digital signatures can provide integrity authentication, 

and source authentication), but not all services.

3.1 Confidentiality

Confidentiality is the property whereby information is not disclosed to unauthorized parties. 

Secrecy is a term that is often used synonymously with confidentiality. Confidentiality using 

cryptography is achieved using encryption to render the information unintelligible except by 

authorized entities. The information may become intelligible again by using decryption. In 

order for encryption to provide confidentiality, the cryptographic algorithm and mode of 

operation must be designed and implemented so that an unauthorized party cannot determine 

the secret or private keys associated with the encryption or be able to derive the plaintext

directly without using the correct keys.

3.2 Data Integrity

Data integrity is a property whereby data has not been modified in an unauthorized manner 

since it was created, transmitted or stored. Modification includes the insertion, deletion and 

substitution of data. Cryptographic mechanisms, such as message authentication codes or 

digital signatures, can be used to detect (with a high probability) both accidental modifications 

(e.g., modifications that sometimes occur during noisy transmissions or by hardware memory 

failures) and deliberate modifications by an adversary. Non-cryptographic mechanisms are also 

often used to detect accidental modifications, but cannot be relied upon to detect deliberate 

modifications. A more detailed treatment of this subject is provided in Appendix A.

In this Recommendation, the statement that a cryptographic algorithm "provides data integrity" 

means that the algorithm is used to detect unauthorized modifications. Authenticating integrity 

is discussed in the next section.

3.3 Authentication

Two types of authentication services can be provided using cryptography: integrity 

authentication and source authentication. 

• An integrity authentication service is used to verify that data has not been modified, 

i.e., this service provides integrity protection. 

• A source authentication service is used to verify the identity of the user or system that 

created information (e.g., a transaction or message).

Several cryptographic mechanisms may be used to provide authentication services. Most 

commonly, digital signatures or message authentication codes are used to provide 

authentication; some key-agreement techniques also provide an authentication service. 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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When multiple individuals are permitted to share the same source authentication information 

(such as a password or cryptographic key), it is sometimes called role-based authentication. 

See [FIPS140]. 

3.4 Authorization

Authorization is concerned with providing an official sanction or permission to perform a 

security function or activity (e.g., accessing a room). Authorization is considered as a security 

service that is often supported by a cryptographic service. Normally, authorization is granted 

only after the execution of a successful source authentication2 service. A non-cryptographic 

analog of the interaction between source authentication and authorization is the examination of 

an individual’s credentials to establish their identity (the source authentication process); after 

verifying the individual's identity and verifying that the individual is authorized access to some 

resource, such as a locked room, the individual is then provided with the key (e.g., an 

authorization key) or password that will allow access to that resource. 

Source authentication can also be used to authorize a role (such as a system administrator or 

audit role), rather than to identify an individual. Once authenticated for a role, an entity is 

authorized for all the privileges associated with that role.

3.5 Non-repudiation

In key management, non-repudiation is a term associated with digital signature keys and digital 

certificates that bind the name of the certificate subject to a public key. When non-repudiation 

is indicated for a digital signature key, it means that the signatures created by that key support 

not only the usual integrity and source authentication services of digital signatures, but also 

may (depending upon the context of the signature) indicate commitment by the certificate 

subject, in the same sense that a handwritten signature on a document may indicate 

commitment to a contract.

A real determination of non-repudiation is a legal decision with many aspects to be considered. 

Cryptographic mechanisms can only be used as one element in this decision (i.e., a digital 

signature can only be used to support a non-repudiation decision).

3.6 Support Services

The basic cryptographic security services discussed above often require other supporting 

services. For example, cryptographic services often require the use of key establishment and 

random number generation services.

3.7 Combining Services

In many applications, a combination of security services (confidentiality, integrity

authentication, source authentication, and support for non-repudiation) is desired. Designers of 

secure systems often begin by considering which security services are needed to protect the 

information contained within and processed by the system. After these services have been 

determined, the designer then considers what mechanisms will best provide these services. Not 

all mechanisms are cryptographic in nature. For example, physical security may be used to 

protect the confidentiality of certain types of data, and identification badges or biometric 

 2 Sometimes referred to as identity authentication.
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identification devices may be used for source authentication. However, cryptographic 

mechanisms consisting of algorithms, keys, and other keying material often provide the most 

cost-effective means of protecting the security of information. This is particularly true in 

applications where the information would otherwise be exposed to unauthorized entities.

When properly implemented, some cryptographic algorithms provide multiple services. The 

following examples illustrate this case:

1. A message authentication code (Section 4.2.3) can provide source authentication, as 

well as integrity authentication if the symmetric keys are unique to each pair of users. 

2. A digital signature algorithm (Section 4.2.4) can provide source authentication and 

integrity authentication, as well as support a non-repudiation decision.

3. Certain modes of encryption can provide confidentiality, integrity authentication, and 

source authentication when properly implemented. These modes should be specifically 

designed to provide these services.

However, it is often the case that different algorithms need to be employed in order to provide 

all the desired services.

Examples:

Consider a system where the secure exchange of information between pairs of Internet 

entities is needed. Some of the exchanged information requires just integrity protection, 

while other information requires both integrity and confidentiality protection. It is also a 

requirement that each entity that participates in an information exchange knows the identity 

of the other entity. 

The designers of this example system decide that a Public Key Infrastructure (PKI) needs 

to be established and that each entity wishing to communicate securely is required to 

physically prove his or her identity to a Registration Authority (RA). This identity-proving 

process requires the presentation of proper credentials, such as a driver’s license, passport 

or birth certificate. After establishing the correct identity, an individual then generates a 

public static key pair; each individual that generates a key pair is considered to be the 

owner of that key pair. The public key of the key pair is provided to the RA, where it is 

incorporated with the key-pair owner’s identifier and other information into a digitally 

signed message for transmission to a Certification Authority (CA). The CA then composes 

the key-pair owner’s public-key certificate by signing the owner's public key and the 

identifier, along with other information. This certificate is returned to the key-pair owner or 

placed in a certificate repository or both. The private key remains under the sole control of 

the owner.

Two types of public key certificates are commonly used: certificates used for key 

establishment (i.e., key agreement or key transport) and certificates used for digital 

signatures.

In the case of key-agreement certificates, two entities wishing to communicate may 

exchange public-key certificates containing public static key-agreement keys that are 

checked by verifying the CA’s signature on the certificate (using the CA’s public key). The 

public static key-agreement key of each of the two entities and each entity's own private 

static key-agreement key are then used in a key-agreement scheme to produce a shared 
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secret that is known by the two entities. The shared secret may then be used to derive one 

or more shared symmetric keys to be used by a symmetric algorithm to provide 

confidentiality and/or integrity protection for data. The receiver of the data protected by the 

symmetric key(s) has assurance that the data came from the other entity indicated by the 

public-key certificate (i.e., source authentication for the symmetric keys has been 

obtained). 

In the case of digital signature certificates, one entity (i.e., a signatory) signs data using the 

private key and sends the signed data to an intended recipient. The recipient obtains the 

signatory’s public key certificate (e.g., from the recipient or some repository), verifies the 

certificate using the CA’s public key, and then uses the public key in the certificate (i.e., 

the public key corresponding to the private key used by the signatory) to verify the 

signature on the received data. By using this process, the recipient obtains assurances of 

both the integrity and the source of the received data.

The above examples provide basic sketches of how cryptographic algorithms may be used to 

support multiple security services. However, it can be easily seen that the security of such 

systems depend on many factors, including:

a. The strength of the entity’s credentials (e.g., driver’s license, passport or birth 

certificate) and the identity authentication process,

b. The strength of the cryptographic algorithms used,

c. The degree of trust placed in the RA and the CA,

d. The strength of the key-establishment protocols, and

e. The care taken by the users in generating their keys and protecting them from 

unauthorized use.

Therefore, the design of a security system that provides the desired security services by making 

use of cryptographic algorithms and sound key-management techniques requires a high degree 

of skill and expertise.
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4 Cryptographic Algorithms

FIPS-approved or NIST-recommended cryptographic algorithms shall be used whenever 

cryptographic services are required. These approved algorithms have received an intensive 

security analysis prior to their approval and continue to be examined to determine that the 

algorithms provide adequate security. Most cryptographic algorithms require cryptographic 

keys or other keying material. In some cases, an algorithm may be strengthened by the use of 

larger keys. This Recommendation advises the users of cryptographic mechanisms on the 

appropriate choices of algorithms and key sizes. 

This section describes the approved cryptographic algorithms that provide security services, 

such as confidentiality, integrity authentication, and source authentication. 

4.1 Classes of Cryptographic Algorithms

There are three basic classes of approved cryptographic algorithms: hash functions, 

symmetric-key algorithms and asymmetric-key algorithms. The classes are defined by the 

number of cryptographic keys that are used in conjunction with the algorithm.

Cryptographic hash functions do not require keys for their basic operation. Hash functions 

generate a relatively small digest (hash value) from a (possibly) large input in a way that is 

fundamentally one-way (i.e., it is difficult to find an input that will produce a given output). 

Hash functions are used as building blocks for key management, for example,

1. To provide source and integrity authentication services (Section 4.2.3) – the hash 

function is used with a key to generate a message authentication code;

2. To compress messages for digital signature generation and verification (Section 4.2.4);

3. To derive keys in key-establishment algorithms (Section 4.2.5); and

4. To generate deterministic random numbers (Section 4.2.7). 

Symmetric-key algorithms (sometimes known as secret-key algorithms) transform data in a 

way that is fundamentally difficult to undo without knowledge of a secret key. The key is 

“symmetric” because the same key is used for a cryptographic operation and its inverse (e.g., 

encryption and decryption). Symmetric keys are often known by more than one entity; 

however, the key shall not be disclosed to entities that are not authorized access to the data 

protected by that algorithm and key. Symmetric key algorithms are used, for example,

1. To provide data confidentiality (Section 4.2.2); the same key is used to encrypt and 

decrypt data; 

2. To provide source and integrity authentication services (Section 4.2.3) in the form of 

Message Authentication Codes (MACs); the same key is used to generate the MAC and 

to validate it. MACs normally employ either a symmetric key-encryption algorithm or a 

cryptographic hash function as their cryptographic primitive; 

3. As part of the key-establishment process (Section 4.2.5); and

4. To generate deterministic random numbers (Section 4.2.7).

Asymmetric-key algorithms, commonly known as public-key algorithms, use two related keys 

(i.e., a key pair) to perform their functions: a public key and a private key. The public key may 

be known by anyone; the private key should be under the sole control of the entity that “owns” 
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the key pair3. Even though the public and private keys of a key pair are related, knowledge of 

the public key cannot be used to determine the private key. Asymmetric algorithms are used, 

for example,

1. To compute digital signatures (Section 4.2.4), and 

2. To establish cryptographic keying material (Section 4.2.5)

4.2 Cryptographic Algorithm Functionality

Security services are fulfilled using a number of different algorithms. In many cases, the same 

algorithm may be used to provide multiple services.

4.2.1 Hash Functions

Many algorithms and schemes that provide a security service use a hash function as a 

component of the algorithm. Hash functions are used by digital signature algorithms (see 

[FIPS186]), Keyed-Hash Message Authentication Codes (HMAC) (see [FIPS198]), keyderivation functions/methods (see [SP800-56A], [SP800-56B], [SP800-56C] and [SP800-

108]), and random number generators (see [SP800-90]). Approved hash functions are defined 

in [FIPS180] and [FIPS202].

A hash function takes an input of arbitrary (although bounded) length and outputs a fixedlength value. Common names for the output of a hash function include hash value, hash, 

message digest, and digital fingerprint. The maximum number of input and output bits is 

determined by the design of the hash function. All approved hash functions are cryptographic 

hash functions. With a well-designed cryptographic hash function, it is not feasible to find a 

message that will produce a given hash value (pre-image resistance), nor is it feasible to find 

two messages that produce the same hash value (collision resistance).

Several hash functions are approved for Federal Government use and are defined in [FIPS180]

and [FIPS 202]. Algorithm standards need to specify either the appropriate size for the hash 

function or provide the hash-function selection criteria if the algorithm can be configured to 

use different hash functions. 

4.2.2 Symmetric-Key Algorithms used for Encryption and Decryption

Encryption is used to provide confidentiality for data. The data to be protected is called 

plaintext when in its original form. Encryption transforms the data into ciphertext. Ciphertext 

can be transformed back into plaintext using decryption. The approved algorithms for 

encryption/decryption are symmetric key algorithms: AES and TDEA. Each of these 

algorithms operates on blocks (chunks) of data during an encryption or decryption operation. 

For this reason, these algorithms are commonly called block cipher algorithms.

4.2.2.1 Advanced Encryption Standard (AES)

The AES algorithm is specified in [FIPS197]. AES encrypts and decrypts data in 128-bit 

blocks, using 128-, 192- or 256-bit keys. The nomenclature for AES for the different key sizes 

is AES-x, where x is the key size (e.g., AES-256). 

 3 Sometimes a key pair is generated by a party that is trusted by the key owner.
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4.2.2.2 Triple DEA (TDEA)

Triple DEA is defined in [SP800-67]. TDEA encrypts and decrypts data in 64-bit blocks, using

three 56-bit keys. Two variations of TDEA have been defined: two-key TDEA (2TDEA), in 

which the first and third keys are identical, and three-key TDEA, in which the three keys are 

all different (i.e., distinct).

The use of two-key TDEA will no longer be approved for applying cryptographic protection 

(e.g., encryption) after December 31, 2015 (see [SP800-131A]); however, two-key TDEA may 

continue to be used for processing already-protected information (e.g., decryption). 

Federal applications shall only use three distinct keys whenever using TDEA for applying 

cryptographic protection after December 31, 2015; see Table 2 in Section 5.6.1 and [SP800-

131A] for further guidance. 

4.2.2.3 Modes of Operation

With a block-cipher encryption operation, the same plaintext block will always encrypt to the 

same ciphertext block whenever the same key is used. If the multiple blocks in a typical 

message are encrypted separately, an adversary can easily substitute individual blocks, 

possibly without detection. Furthermore, certain kinds of data patterns in the plaintext, such as 

repeated blocks, are apparent in the ciphertext. 

Cryptographic modes of operation have been defined to alleviate this problem by combining 

the basic cryptographic algorithm with variable initialization vectors and some sort of feedback 

of the information derived from the cryptographic operation (see the [SP800-38] series of 

publications). The NIST Recommendation for Block Cipher Modes of Operation [SP800-38A]

defines modes of operation for the encryption and decryption of data using block cipher 

algorithms, such as AES and TDEA. Other modes approved for encryption are specified in 

other parts of [SP800-38]; some of these modes also produce message authentication codes 

(see Section 4.2.3). Guidance on the secure use of each mode is provided for each mode, in 

addition to the mode specification.

Note that one of the modes included in [SP800-38A] is the Electronic Codebook (ECB) mode. 

This mode is not recommended for general use, as the ciphertext leaks information about 

plaintext after relatively small amounts of structured data is encrypted.

4.2.3 Message Authentication Codes (MACs)

Message Authentication Codes (MACs) can be used to provide source and integrity 

authentication. A MAC is a cryptographic checksum on the data that is used in order to provide 

assurance that the data has not changed and that the MAC was computed by the expected 

entity. Although non-cryptographic techniques (known as error detection codes) are often used 

to provide message authentication, these codes can be altered by an adversary to effect an 

action to the adversary’s benefit. The use of an approved cryptographic mechanism, such as a 

MAC, can alleviate this problem. In addition, the MAC can provide a recipient with assurance 

that the originator (i.e., the source) of the data is a key holder (i.e., an entity authorized to have 

the key). MACs are often used to authenticate the originator to the recipient when only those 

two parties share the MAC key. 

The computation of a MAC requires the use of (1) a secret key that is known only by the party 

that generates the MAC and by the intended recipient(s) of the MAC, and (2) the data on which 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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the MAC is calculated. The result of the MAC computation is often called a MacTag when 

transmitted; a MacTag is either a full-length or truncated result from the MAC computation. 

Two types of algorithms for computing a MAC have been approved: MAC algorithms that are 

based on block cipher algorithms, and MAC algorithms that are based on hash functions.

4.2.3.1 MACs Using Block Cipher Algorithms

[SP800-38B] defines the CMAC mode: a mode that can be used to compute a MAC using 

approved block cipher algorithms, such as AES and TDEA. [SP 800-38D] defines the GMAC 

mode that can be used with AES.

The key and block size used to compute a MAC based on a block cipher algorithm depends on 

the algorithm used. If the same block cipher is used for both encryption and MAC computation 

in two separate cryptographic operations (e.g., using an encryption mode from [SP800-38A]

and a MAC computed as specified in [SP800-38B]), then the same key shall not be used for 

both the MAC and encryption operations. However, some modes of operation specified in the 

[SP800-38] series provide both encryption and integrity protection using a single key. 

4.2.3.2 MACs Using Hash Functions

[FIPS198] specifies the computation of a MAC using an approved hash function. A variety of 

key sizes are allowed for HMAC, which is the MAC algorithm specified in [FIPS198]; the 

choice of key size depends on the amount of security to be provided to the data and the hash 

function used. See [SP800-107] for further discussions about HMAC, and Section 5.6 of this 

Recommendation (i.e., SP 800-57, Part 1) for further discussion. 

4.2.4 Digital Signature Algorithms

Digital signatures are used to provide source authentication, integrity authentication and 

support for non-repudiation. Digital signatures are used in conjunction with hash functions and 

are computed on data of any length (up to a limit that is determined by the hash function). 

[FIPS186] specifies algorithms that are approved for the computation of digital signatures4. It 

defines the Digital Signature Algorithm (DSA) and adopts the RSA algorithm, as specified in 

[ANSX9.31] and [PKCS#1] (version 1.5 and higher), and the ECDSA algorithm, as specified 

in [ANSX9.62]. 

[FIPS186] also specifies several approved key sizes for each of these algorithms, and includes 

methods for generating the algorithm's key pairs and any other parameters needed for digital 

signature generation and verification. Note that older systems (legacy systems) used smaller 

key sizes than those currently provided in [FIPS186]. Digital signature generation shall be 

performed using keys that meet or exceed the key sizes specified in [FIPS186] and using key 

pairs that are generated in accordance with [FIPS186]. Smaller key sizes shall only be used to 

verify signatures that were generated using those smaller keys. See [SP800-131A].

4.2.5 Key Establishment Schemes

Automated key-establishment schemes are used to set up keys to be used between 

communicating entities. Two types of automated key-establishment schemes are defined: key 

 4 Two general types of digital signature methods are discussed in literature: digital signatures with appendix, and 

digital signatures with message recovery. [FIPS186] specifies algorithms for digital signatures with appendix, and 

is the digital signature method that is discussed in this Recommendation.
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transport and key agreement. Approved key-establishment schemes are provided in [SP800-

56A] and [SP800-56B].

Key transport is the distribution of a key (and other keying material) from one entity (the 

sender) to another entity (the receiver). The keying material is encrypted by the sending entity 

and decrypted by one or more receiving entities. 

• If a symmetric algorithm (e.g., AES) is used to transport a key, the algorithm is used to 

wrap (i.e., encrypt) the keying material to be distributed; the sending and receiving 

entities need to know the symmetric key-wrapping key (i.e., the key-encrypting key).

See Section 4.2.5.4 for further discussion on key encryption and key wrapping.

• If a public-key algorithm is used for key transport, one key of a key pair is used to 

encrypt the key to be established, and the other key is used for decryption. In this case, 

the sending entity encrypts the keying material using the receiving entity’s public key, 

and the receiving entity decrypts the received keying material using the associated 

private key. 

Key agreement is the participation by both entities in the creation of shared keying material. 

This may be accomplished using either asymmetric (public-key) or symmetric-key techniques. 

• If an asymmetric algorithm is used, each entity has either a static key pair or an 

ephemeral key pair or both. 

• If a symmetric-key algorithm is used, each entity shares the same symmetric keywrapping key.

4.2.5.1 Discrete-Log Key-Agreement Schemes

[SP800-56A] specifies key-establishment schemes that use discrete-logarithm-based publickey algorithms. These schemes are specified using either finite-field math (the form of math 

that most of us use) or elliptic curve math. 

With the key-establishment schemes specified in [SP800-56A], a party may own and use an 

ephemeral key, a static key, or both an ephemeral and a static key in a single key-agreement 

transaction. The ephemeral key is used to provide a new secret for each key-establishment

transaction, while the static key (if used in a PKI with public-key certificates) provides for the 

authentication of the owner. 

[SP800-56A] also provides a key-confirmation method for most of its schemes to obtain 

assurance that each party has agreed upon the same keying material (see Section 4.2.5.5 for a 

discussion of key confirmation).

4.2.5.2 Key Establishment Using Integer-Factorization Schemes 

[SP800-56B] provides key-establishment schemes that use integer-factorization-based publickey algorithms (e.g., RSA). These schemes are provided in [SP 800-56B] for both key 

agreement and key transport, and, in some cases, key confirmation can also be provided.

In these schemes, one party always owns and uses a key pair, and the other party may or may 

not use a key pair, depending on the scheme. Only static keys are used in the [SP800-56B] 

schemes; ephemeral keys are not used.
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4.2.5.3 Security Properties of the Key-Establishment Schemes

Cryptographic protocol designers need to understand the security properties of the schemes in 

order to assure that the desired capabilities are available to the user. In general, schemes where 

each party uses both an ephemeral and a static key provide more security properties than 

schemes using fewer keys. However, it may not be practical for both parties to use both static 

and ephemeral keys in certain applications. For example, in email applications, it is desirable 

to send messages to other parties who are not on-line; in this case, the receiver cannot be 

expected to provide an ephemeral key to establish the message-encrypting key during a 

[SP800-56A] key-agreement scheme. For the schemes in [SP800-56B], ephemeral keys are 

never used.

Both [SP80056A] and [SP800-56B] include discussions of the security properties of each of its 

schemes.

4.2.5.4 Key Encryption and Key Wrapping

Key encryption provides confidentiality protection for a key by encrypting that key using a 

key-encrypting key; decryption reverses the process using the same key. Key wrapping 

provides both confidentiality and integrity protection for a key using a key-wrapping key to 

both encrypt and integrity protect; key unwrapping decrypts the ciphertext key and verifies its 

integrity. Although the key-protection services are slightly different and use different methods, 

the keys are generated in the same manner. The terms are often used interchangeably, but this 

Recommendation will use the terms “key wrapping” and “key unwrapping.”

Key wrapping and unwrapping use a symmetric algorithm, such as AES. Several methods for 

key wrapping and unwrapping have been specified or referenced in [SP800-38F].

4.2.5.5 Key Confirmation

Key confirmation is used by two parties in a key-establishment process to provide assurance 

that common keying material and/or a shared secret5 has been established. The assurance may 

be provided to only one party (unilateral) or it may be provided to both parties (bilateral). The 

assurance may be provided as part of the key-establishment scheme, or it may be provided by 

some action that takes place outside of the scheme. For example, after a key is established, two 

parties may provide assurance (i.e., a confirmation) to one another that they possess the same 

key by demonstrating their ability to encrypt and decrypt data intended for each other. 

[SP800-56A] provides for unilateral key confirmation for schemes where one party has a static 

key-establishment key, and bilateral key confirmation for schemes where both parties have 

static key-establishment keys. A total of ten key-confirmation schemes are provided, seven of 

which are unilateral, and three of which are bilateral.

[SP800-56B] provides for unilateral key confirmation from the responder, in the case of a key 

agreement scheme, and from the receiver, in the case of a key-transport scheme. Initiator and 

bilateral key confirmation are also provided for one family of key-agreement schemes.

 5 An intermediate value computed during a key-agreement scheme.
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4.2.6 Key Establishment Protocols

Key establishment protocols use key-establishment schemes in order to specify the processing 

necessary to establish a key. However, key-establishment protocols also specify message flow 

and format. Key-establishment protocols need to be carefully designed to not give secret 

information to a potential attacker. For example, a protocol that indicates abnormal conditions, 

such as an integrity error, may permit an attacker to confirm or reject an assumption regarding 

secret data. Alternatively, if the time or power required to perform certain computations are 

based upon the value of the secret or private key in use, then an attacker may be able to deduce 

the key from observed fluctuations. 

Therefore, it is best to design key-establishment protocols so that:

1. The protocols do not provide for an early exit from the protocol upon detection of a 

single error,

2. The protocols trigger an alarm after a certain reasonable number of detected error 

conditions, and

3. The key-dependent computations are obscured from the observer in order to prevent or 

minimize the detection of key-dependent characteristics.

4.2.7 Random Bit Generation

Random bit generators (RBGs) (also called random number generators (RNGs)) are required 

for the generation of keying material (e.g., keys and IVs). RBGs generate sequences of random 

bits (e.g., 010011); technically, RNGs translate those bits into numbers (e.g., 010011 is 

translated into the number 19). However, the use of the term “random number generator” 

(RNG) is commonly used to refer to both concepts

Two classes of RBGs are defined: deterministic and non-deterministic. Deterministic Random 

Bit Generators (DRBGs), sometimes called deterministic random number generators or 

pseudorandom number generators, use cryptographic algorithms and the associated keying 

material to generate pseudorandom bits from an initial value, called a seed, that provides 

entropy (i.e., randomness) to the process. Depending on the implemented DRBG design or the 

environment, additional entropy may never be introduced again, although such additional 

entropy is recommended. [SP800-90A] specifies DRBG algorithms that may be used to 

generate random bits for cryptographic applications (e.g., key or IV generation).

Non-deterministic Random Bit Generators (NRBGs), sometimes called true RNGs, use some 

unpredictable physical source that is outside human control to introduce new entropy for every 

bit output by the NRBG. The unpredictable source is commonly known as an entropy source. 

[SP800-90B] provides guidance on the implementation and testing of entropy sources.

[SP800-90C] has been developed to provide guidance on the construction of DRBGs and 

NRBGs from the algorithms in [SP800-90A] and entropy sources that comply with [SP800-

90B]. 
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5 General Key Management Guidance

This section classifies the different types of keys and other cryptographic information 

according to their uses; discusses cryptoperiods and recommends appropriate cryptoperiods for 

each key type; provides recommendations and requirements for other keying material;

introduces assurance of domain-parameter validity, public-key validity, and private-key 

possession; discusses the implications of the compromise of keying material; and provides 

guidance on the selection, implementation, and replacement of cryptographic algorithms and 

key sizes according to their security strengths.

5. 1 Key Types and Other Information

There are several different types of cryptographic keys, each used for a different purpose. In 

addition, there is other information that is specifically related to cryptographic algorithms and 

keys.

5.1.1 Cryptographic Keys 

Several different types of keys are defined. The keys are identified according to their 

classification as public, private or symmetric keys, and as to their use. For public and private 

key-agreement keys, their status as static or ephemeral keys is also specified. See Table 5 in 

Section 6.1.1 for the required protections for each type of information.

1. Private signature key: Private signature keys are the private keys of asymmetric 

(public) key pairs that are used by public-key algorithms to generate digital signatures 

with possible long-term implications. When properly handled, private signature keys 

can be used to provide source authentication, integrity authentication and support the 

non-repudiation of messages, documents or stored data.

2. Public signature-verification key: A public signature-verification key is the public key 

of an asymmetric (public) key pair that is used by a public-key algorithm to verify 

digital signatures that are intended to provide source authentication, integrity

authentication and support the non-repudiation of messages, documents or stored data.

3. Symmetric authentication key: Symmetric authentication keys are used with symmetrickey algorithms to provide source authentication and integrity authentication of 

communication sessions, messages, documents or stored data. Note that for 

authenticated-encryption modes of operation for a symmetric key algorithm, a single 

key is used for both authentication and encryption.

4. Private authentication key: A private authentication key is the private key of an 

asymmetric (public) key pair that is used with a public-key algorithm to provide 

assurance of the identity of an originating entity (i.e., source authentication) when 

establishing an authenticated communication session6

.

5. Public authentication key: A public authentication key is the public key of an 

asymmetric (public) key pair that is used with a public-key algorithm to provide 

 6 While integrity protection is also provided, it is not the primary intention of this key.
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assurance of the identity of an originating entity (i.e., source authentication) when 

establishing an authenticated communication session7

.

6. Symmetric data-encryption key: These keys are used with symmetric-key algorithms to 

apply confidentiality protection to information (i.e., to encrypt the information). The 

same key is also used to remove the confidentiality protection (i.e., to decrypt the 

information). Note that for authenticated-encryption modes of operation for a 

symmetric key algorithm, a single key is used for both authentication and encryption.

7. Symmetric key-wrapping key: Symmetric key-wrapping keys (sometimes called keyencrypting keys) are used to encrypt other keys using symmetric-key algorithms. The 

key-wrapping key used to encrypt a key is also used to reverse the encryption operation 

(i.e., to decrypt the encrypted key). Depending on the algorithm with which the key is 

used, the key may also be used to provide integrity protection.

8. Symmetric random number generation keys: These keys are used to generate random 

numbers or random bits. 

9. Symmetric master key: A symmetric master key is used to derive other symmetric keys 

(e.g., data-encryption keys or key-wrapping keys) using symmetric cryptographic 

methods. The master key is also known as a key-derivation key.

10. Private key-transport key: Private key-transport keys are the private keys of 

asymmetric (public) key pairs that are used to decrypt keys that have been encrypted 

with the corresponding public key using a public-key algorithm. Key-transport keys are 

usually used to establish keys (e.g., key-wrapping keys, data-encryption keys or MAC 

keys) and, optionally, other keying material (e.g., Initialization Vectors). 

11. Public key-transport key: Public key-transport keys are the public keys of asymmetric 

(public) key pairs that are used to encrypt keys using a public-key algorithm. These 

keys are used to establish keys (e.g., key-wrapping keys, data-encryption keys or MAC 

keys) and, optionally, other keying material (e.g., Initialization Vectors). The encrypted 

form of the established key might be stored for later decryption using the private keytransport key.

12. Symmetric key-agreement key: These symmetric keys are used to establish keys (e.g., 

key-wrapping keys, data-encryption keys, or MAC keys) and, optionally, other keying 

material (e.g., Initialization Vectors) using a symmetric key-agreement algorithm.

13. Private static key-agreement key: Private static key-agreement keys are the long-term 

private keys of asymmetric (public) key pairs that are used to establish keys (e.g., keywrapping keys, data-encryption keys, or MAC keys) and, optionally, other keying 

material (e.g., Initialization Vectors). 

14. Public static key-agreement key: Public static key-agreement keys are the long-term 

public keys of asymmetric (public) key pairs that are used to establish keys (e.g., keywrapping keys, data-encryption keys, or MAC keys) and, optionally, other keying 

material (e.g., Initialization Vectors). 

 7 While integrity protection is also provided, it is not the primary intention of this key.
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15. Private ephemeral key-agreement key: Private ephemeral key-agreement keys are the 

short-term private keys of asymmetric (public) key pairs that are used only once8 to 

establish one or more keys (e.g., key-wrapping keys, data-encryption keys, or MAC 

keys) and, optionally, other keying material (e.g., Initialization Vectors). 

16. Public ephemeral key-agreement key: Public ephemeral key-agreement keys are the 

short-term public keys of asymmetric key pairs that are used in a single keyestablishment transaction9 to establish one or more keys (e.g., key-wrapping keys, dataencryption keys, or MAC keys) and, optionally, other keying material (e.g., 

Initialization Vectors). 

17. Symmetric authorization key: Symmetric authorization keys are used to provide 

privileges to an entity using a symmetric cryptographic method. The authorization key 

is known by the entity responsible for monitoring and granting access privileges for 

authorized entities and by the entity seeking access to resources. 

18. Private authorization key: A private authorization key is the private key of an 

asymmetric (public) key pair that is used to provide privileges to an entity. 

19. Public authorization key: A public authorization key is the public key of an asymmetric 

(public) key pair that is used to verify privileges for an entity that knows the associated 

private authorization key. 

5.1.2 Other Cryptographic or Related Information

Other information used in conjunction with cryptographic algorithms and keys also needs to be 

protected. See Table 6 in Section 6.1.2 for the required protections for each type of 

information.

1. Domain Parameters: Domain parameters are used in conjunction with some public-key

algorithms to generate key pairs, to create digital signatures or to establish keying material. 

2. Initialization Vectors: Initialization vectors (IVs) are used by several modes of operation 

for encryption and decryption (see Section 4.2.2.3) and for the computation of MACs using 

block cipher algorithms (see Section 4.2.3.1) 

3. Shared Secrets: Shared secrets are generated during a key-agreement process as defined in 

[SP800-56A] and [SP800-56B]. Shared secrets shall be protected and handled in the same 

manner as cryptographic keys. If a FIPS 140-validated cryptographic module is being used, 

then the module is used to provide the protection for the shared secrets. 

4. RBG seeds: RBG seeds are used in the generation of deterministic random bits (e.g., used 

to generate keying material that must remain secret or private).

5. Other public information: Public information (e.g., a nonce) is often used in the keyestablishment process. 

 8 In some cases ephemeral keys are used more than once, though within a single “session”. For example, when

Diffie-Hellman is used in S/MIME CMS, the sender may generate one ephemeral key pair per message, and 

combine the private key separately with each recipient’s public key.

9 The public ephemeral key-agreement key of a sender may be retained by the receiver for later use in decrypting 

a stored (encrypted) message for which the ephemeral key pair was generated.
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6. Other secret information: Secret information may be included in the seeding of an RBG or 

in the establishment of keying material.

7. Intermediate Results: The intermediate results of cryptographic operations using secret 

information must be protected. Intermediate results shall not be available for purposes 

other than as intended.

8. Key-control information: Information related to the keying material (e.g., the identifier, 

purpose, or a counter) must be protected to ensure that the associated keying material can 

be correctly used. The key-control information is included in the metadata associated with 

the key (see Section 6.2.3.1). 

9. Random numbers (or bits): The random numbers created by a random bit generator should

be protected when retained. When used directly as keying material or in its generation, the 

random bits shall be protected as discussed in Section 6.

10. Passwords: A password is used to acquire access to privileges and can be used as a 

credential in a source-authentication mechanism. A password can also be used to derive 

cryptographic keys that are used to protect and access data in storage, as specified in 

[SP800-132].

11. Audit information: Audit information contains a record of key-management events.

5.2 Key Usage

In general, a single key shall be used for only one purpose (e.g., encryption, integrity 

authentication, key wrapping, random bit generation, or digital signatures). There are several 

reasons for this:

1. The use of the same key for two different cryptographic processes may weaken the 

security provided by one or both of the processes.

2. Limiting the use of a key limits the damage that could be done if the key is 

compromised. 

3. Some uses of keys interfere with each other. For example, consider a key pair used for 

both key transport and digital signatures. In this case, the private key is used as both a 

private key-transport key to decrypt the encrypted keys and as a private signature key to 

apply digital signatures. It may be necessary to retain the private key-transport key 

beyond the cryptoperiod of the corresponding public key-transport key in order to 

decrypt the encrypted keys needed to access encrypted data. On the other hand, the 

private signature key shall be destroyed at the expiration of its cryptoperiod to prevent 

its compromise (see Section 5.3.6). In this example, the longevity requirements for the 

private key-transport key and the private digital-signature key contradict each other.

This principle does not preclude using a single key in cases where the same process can 

provide multiple services. This is the case, for example, when a digital signature provides 

integrity authentication and source authentication using a single digital signature, or when a 

single symmetric key can be used to encrypt and authenticate data in a single cryptographic 

operation (e.g., using an authenticated-encryption operation, as opposed to separate encryption 

and authentication operations). Also, refer to Section 3.7.
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This Recommendation permits the use of a private key-transport or key-agreement key to 

generate a digital signature for the following special case:

When requesting the (initial) certificate for a static key-establishment key, the 

corresponding private key may be used to sign the certificate request. Also refer to Section 

8.1.5.1.1.2.

5.3 Cryptoperiods

A cryptoperiod is the time span during which a specific key is authorized for use by legitimate 

entities, or the keys for a given system will remain in effect. A suitably defined cryptoperiod:

1. Limits the amount of information protected by a given key that is available for 

cryptanalysis,

2. Limits the amount of exposure if a single key is compromised,

3. Limits the use of a particular algorithm (e.g., to its estimated effective lifetime), 

4. Limits the time available for attempts to penetrate physical, procedural, and logical 

access mechanisms that protect a key from unauthorized disclosure,

5 Limits the period within which information may be compromised by inadvertent 

disclosure of keying material to unauthorized entities, and

6. Limits the time available for computationally intensive cryptanalytic attacks (in 

applications where long-term key protection is not required).

Sometimes cryptoperiods are defined by an arbitrary time period or maximum amount of data 

protected by the key. However, trade-offs associated with the determination of cryptoperiods 

involve the risk and consequences of exposure, which should be carefully considered when 

selecting the cryptoperiod (see Section 5.6.4).

5.3.1 Risk Factors Affecting Cryptoperiods

Among the factors affecting the length of a cryptoperiod are:

1. The strength of the cryptographic mechanisms (e.g., the algorithm, key length, block 

size, and mode of operation), 

2. The embodiment of the mechanisms (e.g., a [FIPS140] Level 4 implementation or a 

software implementation on a personal computer), 

3. The operating environment (e.g., a secure limited-access facility, open office 

environment, or publicly accessible terminal), 

4. The volume of information flow or the number of transactions, 

5. The security life of the data,

6. The security function (e.g., data encryption, digital signature, key derivation, or key 

protection), 

7. The re-keying method (e.g., keyboard entry, re-keying using a key loading device 

where humans have no direct access to key information, or remote re-keying within a 

PKI), 
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8. The key update or key-derivation process,

9. The number of nodes in a network that share a common key, 

10. The number of copies of a key and the distribution of those copies, 

11. Personnel turnover (e.g., CA system personnel), 

12. The threat to the information from adversaries (e.g., whom the information is protected 

from, and what are their perceived technical capabilities and financial resources to 

mount an attack), and 

13. The threat to the information from new and disruptive technologies (e.g., quantum 

computers).

In general, short cryptoperiods enhance security. For example, some cryptographic algorithms 

might be less vulnerable to cryptanalysis if the adversary has only a limited amount of 

information encrypted under a single key. On the other hand, where manual key-distribution 

methods are subject to human error and frailty, more frequent key changes might actually 

increase the risk of key exposure. In these cases, especially when very strong cryptography is 

employed, it may be more prudent to have fewer, well-controlled manual key distributions,

rather than more frequent, poorly controlled manual key distributions. 

In general, where strong cryptography is employed, physical, procedural, and logical accessprotection considerations often have more impact on cryptoperiod selection than do algorithm 

and key-size factors. In the case of approved algorithms, modes of operation, and key sizes, 

adversaries may be able to access keys through the penetration or subversion of a system with 

less expenditure of time and resources than would be required to mount and execute a 

cryptographic attack.

5.3.2 Consequence Factors Affecting Cryptoperiods

The consequences of exposure are measured by the sensitivity of the information, the criticality 

of the processes protected by the cryptography, and the cost of recovery from the compromise 

of the information or processes. Sensitivity refers to the lifespan of the information being 

protected (e.g., 10 minutes, 10 days or 10 years) and the potential consequences of a loss of 

protection for that information (e.g., the disclosure of the information to unauthorized entities). 

In general, as the sensitivity of the information or the criticality of the processes protected by 

cryptography increase, the length of the associated cryptoperiods should decrease in order to 

limit the damage that might result from each compromise. This is subject to the caveat 

regarding the security and integrity of the re-keying, key update or key-derivation process (see 

Sections 8.2.3 and 8.2.4). Short cryptoperiods may be counter-productive, particularly where 

denial of service is the paramount concern, and there is a significant potential for error in the 

re-keying, key update or key-derivation process.

5.3.3 Other Factors Affecting Cryptoperiods

5.3.3.1 Communications versus Storage

Keys that are used for confidentiality protection of communication exchanges may often have 

shorter cryptoperiods than keys used for the protection of stored data. Cryptoperiods are 

generally made longer for stored data because the overhead of re-encryption associated with 

changing keys may be burdensome.
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5.3.3.2 Cost of Key Revocation and Replacement

In some cases, the costs associated with changing keys are painfully high. Examples include 

decryption and subsequent re-encryption of very large databases, decryption and re-encryption 

of distributed databases, and revocation and replacement of a very large number of keys (e.g., 

where there are very large numbers of geographically and organizationally distributed key 

holders). In such cases, the expense of the security measures necessary to support longer 

cryptoperiods may be justified (e.g., costly and inconvenient physical, procedural, and logical

access security; and the use of cryptography strong enough to support longer cryptoperiods,

even where this may result in significant additional processing overhead). In other cases, the 

cryptoperiod may be shorter than would otherwise be necessary; for example, keys may be 

changed frequently in order to limit the period of time that the key-management system 

maintains status information. 

5.3.4 Asymmetric Key Usage Periods and Cryptoperiods

For key pairs, each key of the pair has its own cryptoperiod. One key of the key pair is used to 

apply cryptographic protection (e.g., create a digital signature), and its cryptoperiod can be 

considered as an “originator-usage period.” The other key of the key pair is used to process the 

protected information (e.g., verify a digital signature); its cryptoperiod is considered to be a 

“recipient-usage period.” The key pair's originator and recipient-usage periods typically begin 

at the same time, but the recipient-usage period may extend beyond the originator-usage 

period. For example:

• In the case of digital signature key pairs, the private signature key is used to sign data 

(i.e., apply cryptographic protection), so its cryptoperiod is considered to be an 

originator-usage period. The public signature-verification key is used to verify digital 

signatures (i.e., process already-protected information); its cryptoperiod is considered 

to be a recipient-usage period. 

For a private signature key that is used to generate digital signatures as a proof-oforigin (i.e., for source authentication), the originator-usage period (i.e., the period 

during which the private key may be used to generate signatures) is often shorter than 

the recipient-usage period (i.e., the period during which the signature may be verified).

In this case, the private key is intended for use for a fixed period of time, after which 

time the key owner shall destroy10 the private key. The public key may be available for 

a longer period of time for verifying signatures. 

The cryptoperiod of a private source-authentication key that is used to sign challenge 

information is basically the same as the cryptoperiod of the associated public key (i.e., 

the public source-authentication key). That is, when the private key will not be used to 

sign challenges, the public key is no longer needed. In this case, the originator and 

recipient-usage periods are the same.

 10 A simple deletion of the keying material might not completely obliterate the information. For example, erasing 

the information might require overwriting that information multiple times with other non-related information, 

such as random bits, or all zero or one bits. Keys stored in memory for a long time can become “burned in”. 

Splitting the key into components that are frequently updated can mitigate this problem (see [DiCrescenzo]).
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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• For key transport keys, the public key-transport key is used to apply protection (i.e., 

encrypt), so its cryptoperiod would be considered as an originator-usage period; the 

private key-transport key is used to decrypt, so its cryptoperiod would be considered as 

the recipient-usage period. The originator-usage period (i.e., the period during which 

the public key may be used for encryption) is often shorter than the recipient-usage 

period (i.e., the period during which the encrypted information may be decrypted).

• For key-agreement algorithms, the cryptoperiods of the two keys of the key pair are 

usually the same.

Where public keys are distributed in public-key certificates, each certificate has a validity 

period, indicated by the notBefore and notAfter dates in the certificate. Certificates may be 

renewed, i.e., a new certificate containing the same public key may be issued with a new 

validity period. The range of time covered by the validity periods of the original certificate and 

all renewed certificates for the same public key shall not extend beyond the beginning and end 

dates of the cryptoperiod for the key of the key pair used to apply protection (i.e., the key with 

the originator-usage period).

See Section 5.3.6 for guidance regarding specific key types. 

5.3.5 Symmetric Key Usage Periods and Cryptoperiods 

For symmetric keys, a single key is used for both applying the protection (e.g., encrypting or 

computing a MAC) and processing the protected information (e.g., decrypting the encrypted

information or verifying a MAC). The period of time during which cryptographic protection 

may be applied to data is called the originator-usage period, and the period of time during 

which the protected information is processed is called the recipient-usage period. A symmetric 

key shall not be used to provide protection after the end of the originator-usage period. The 

recipient-usage period may extend beyond the originator-usage period (see Figure 1). This 

permits all information that has been protected by the originator to be processed by the 

recipient for an extended period of time after protection has been applied. However, in many 

cases, the originator and recipient-usage periods are the same. The (total) “cryptoperiod” of a 

symmetric key is the period of time from the beginning of the originator-usage period to the 

end of the recipient-usage period, although the originator-usage period has historically been 

used as the cryptoperiod for the key. 

Note that in some cases, predetermined cryptoperiods may not be adequate for the security life 

of the protected data. If the required security life exceeds the cryptoperiod, then the protection 

will need to be reapplied using a new key. 
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Figure 1: Symmetric key cryptoperiod

Examples of the use of the usage periods include:

a. When a symmetric key is used only for securing communications, the period of time 

from the originator’s application of protection to the recipient’s processing may be 

negligible. In this case, the key is authorized for either purpose during the entire 

cryptoperiod, i.e., the originator-usage period and the recipient-usage period are the 

same. 

b. When a symmetric key is used to protect stored information, the originator-usage

period (when the originator applies cryptographic protection to stored information) may 

end much earlier than the recipient-usage period (when the stored information is 

processed). In this case, the cryptoperiod begins at the initial time authorized for the 

application of protection with the key, and ends with the latest time authorized for 

processing using that key. In general, the recipient-usage period for stored information 

will continue beyond the originator-usage period so that the stored information may be 

authenticated or decrypted at a later time.

c. When a symmetric key is used to protect stored information, the recipient-usage period 

may start after the beginning of the originator-usage period as shown in Figure 1. For 

example, information may be encrypted before being stored on some storage media. At 

some later time, the key may be distributed in order to decrypt and recover the 

information.

5.3.6 Cryptoperiod Recommendations for Specific Key Types

The key type, usage environment and data characteristics described above may affect the 

cryptoperiod required for a given key. Some general cryptoperiod recommendations for 

various key types are suggested below. Note that the cryptoperiods suggested are only rough 

order-of-magnitude guidelines; longer or shorter cryptoperiods may be warranted, depending 

on the application and environment in which the keys will be used. However, when assigning a 

longer cryptoperiod than that suggested below, serious consideration should be given to the 

risks associated with doing so (see Section 5.3.1). Most of the suggested cryptoperiods are on 
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the order of 1 to 2 years, based on 1) a desire for maximum operational efficiency and 2) 

assumptions regarding the minimum criteria for the usage environment (see [FIPS140], 

[SP800-14], and [SP800-37]). The factors described in Sections 5.3.1 through 5.3.3 should be 

used to determine actual cryptoperiods for specific usage environments.

1. Private signature key: 

a. Type Considerations: In general, the cryptoperiod of a private signature key may be 

shorter than the cryptoperiod of the corresponding public signature-verification key. 

When the corresponding public key has been certified by a CA, the cryptoperiod ends 

when the notAfter date is reached on the last certificate issued for the public key11.

b. Cryptoperiod: Given the use of approved algorithms and key sizes, and an 

expectation that the security of the key-storage and use environment will increase as the 

sensitivity and/or criticality of the processes for which the key provides integrity 

protection increases, a maximum cryptoperiod of about one to three years is 

recommended. The key shall be destroyed at the end of its cryptoperiod.

2. Public signature-verification key: 

a. Type Considerations: In general, the cryptoperiod of a public signature-verification

key may be longer than the cryptoperiod of the corresponding private signature key. 

The cryptoperiod is, in effect, the period during which any signature computed using 

the corresponding private signature key needs to be verified. A longer cryptoperiod for 

the public signature-verification key (than the private signature key) poses a relatively

minimal security concern.

b. Cryptoperiod: The cryptoperiod may be on the order of several years, though due to 

the long exposure of protection mechanisms to hostile attack, the reliability of the 

signature is reduced with the passage of time. That is, for any given algorithm and key 

size, vulnerability to cryptanalysis is expected to increase with time. Although choosing 

the strongest available algorithm and a large key size can minimize this vulnerability to 

cryptanalysis, the consequences of exposure to attacks on physical, procedural, and 

logical access-control mechanisms for the private key are not affected.

Some systems use a cryptographic timestamping function to place an unforgeable 

timestamp on each signed message. Even though the cryptoperiod of the private 

signature key has expired, the corresponding public signature-verification key may be 

used to verify signatures on messages whose timestamps are within the cryptoperiod of 

the private signature key. In this case, one is relying on the cryptographic timestamp 

function to assure that the message was signed within the signature key's originatorusage period.

3. Symmetric authentication key: 

a. Type Considerations: The cryptoperiod of a symmetric authentication key12 depends 

on the sensitivity of the type of information it protects and the protection afforded by 

 11 Multiple consecutive certificates may be issued for the same public key, presumably with different notBefore

and notAfter validity dates. 

12 Used to enable data integrity and source authentication.
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the key. For very sensitive information, the authentication key may need to be unique to 

the protected information. For less sensitive information, suitable cryptoperiods may 

extend beyond a single use of the key. The originator-usage period of a symmetric 

authentication key applies to the use of that key in applying the original cryptographic 

protection for the information (e.g., computing the MAC); new MACs shall not be 

computed on information using that key after the end of the originator-usage period. 

However, the key may need to be available to verify the MAC on the protected data 

beyond the originator-usage period (i.e., the recipient-usage period extends beyond the 

originator-usage period). The recipient-usage period is the period during which a MAC 

generated during the originator-usage period needs to be verified. Note that if a MAC 

key is compromised, it may be possible for an adversary to modify the data and then 

recalculate the MAC.

b. Cryptoperiod: Given the use of approved algorithms and key sizes, and an 

expectation that the security of the key-storage and use environment will increase as the 

sensitivity and/or criticality of the processes for which the key provides integrity 

protection increases, a maximum originator-usage period of up to two years is 

recommended, and a maximum recipient-usage period of three years beyond the end of 

the originator-usage period is recommended.

4. Private authentication key: 

a. Type Considerations: A private authentication key13 may be used multiple times. A 

Certification Authority, for example, could certify the corresponding public key. In 

most cases, the cryptoperiod of the private authentication key is the same as the 

cryptoperiod of the corresponding public key. 

b. Cryptoperiod: An appropriate cryptoperiod for a private authentication key would be 

one to two years, depending on its usage environment and the sensitivity/criticality of 

the authenticated information.

5. Public authentication key: 

a. Type Considerations: In most cases, the cryptoperiod of a public authentication key 

is the same as the cryptoperiod of the corresponding private authentication key. The 

cryptoperiod is, in effect, the period during which the identity of the originator of 

information protected by the corresponding private authentication key needs to be 

verified, i.e., the information source needs to be authenticated14.

b. Cryptoperiod: An appropriate cryptoperiod for the public authentication key would 

be one to two years, depending on its usage environment and the sensitivity/criticality 

of the authenticated information.

6. Symmetric data-encryption key: 

a. Type Considerations: A symmetric data-encryption key is used to protect stored data, 

messages or communications sessions. Based primarily on the consequences of 

compromise, a data-encryption key that is used to encrypt large volumes of information 

 13 Which may be used to enable data integrity and source authentication, as well as non-repudiation.

14 While integrity protection is also provided, it is not the primary intention of this key.
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over a short period of time (e.g., for link encryption) should have a relatively short 

originator-usage period. An encryption key used to encrypt less information over time 

could have a longer originator-usage period. The originator-usage period of a 

symmetric data-encryption key applies to the use of that key in applying the original 

cryptographic protection for information (i.e., encrypting the information) (see Section 

5.3.5). 

During the originator-usage period, an encryption of the information may be performed 

using the data-encryption key; the key shall not be used for performing an encryption 

operation on information beyond this period. However, the key may need to be 

available to decrypt the protected data beyond the originator-usage period (i.e., the 

recipient-usage period may need to extend beyond the originator-usage period). 

b. Cryptoperiod: The originator-usage period recommended for the encryption of large 

volumes of information over a short period of time (e.g., for link encryption) is on the 

order of a day or a week. An encryption key used to encrypt smaller volumes of 

information might have an originator-usage period of up to two years. A maximum 

recipient-usage period of three years beyond the end of the originator-usage period is 

recommended. 

In the case of symmetric data-encryption keys that are used to encrypt single messages 

or single communications sessions, the lifetime of the protected data could be months 

or years because the encrypted messages may be stored for later reading. Where 

information is maintained in encrypted form, the symmetric data-encryption keys need 

to be maintained until that information is re-encrypted under a new key or destroyed. 

Note that confidence in the confidentiality of the information is reduced with the 

passage of time. 

7. Symmetric key-wrapping key: 

a. Type Considerations: A symmetric key-wrapping key that is used to wrap (i.e., 

encrypt and integrity protect) very large numbers of keys over a short period of time 

should have a relatively short originator-usage period. If a small number of keys are 

wrapped, the originator-usage period of the key-wrapping key could be longer. The 

originator-usage period of a symmetric key-wrapping key applies to the use of that key 

in providing the key-wrapping protection for the keys; a wrapping operation shall not

be performed using a key-wrapping key whose originator-usage period has expired.

However, the key-wrapping key may need to be available to unwrap the protected keys 

(i.e., decrypt and verify the integrity of the wrapped keys) beyond the originator-usage

period (i.e., the recipient-usage period may need to extend beyond the originator-usage

period); the recipient-usage period is the period of time during which keys wrapped 

during the key-wrapping key's originator-usage period may need to be unwrapped.

Some symmetric key-wrapping keys are used for only a single message or 

communications session. In the case of these very short-term key-wrapping keys, an 

appropriate cryptoperiod (i.e., which includes both the originator and recipient-usage

periods) is a single communication session. It is assumed that the wrapped key will not 

be retained in its wrapped form, so the originator-usage period and recipient-usage 

period of the key-wrapping key is the same. In other cases, key-wrapping keys may be 

retained so that the files or messages encrypted by the wrapped keys may be recovered 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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later on. In this case the recipient-usage period may be significantly longer than the 

originator-usage period of the key-wrapping key, and cryptoperiods lasting for years 

may be employed.

b. Cryptoperiod: The recommended originator-usage period for a symmetric keywrapping key that is used to wrap very large numbers of keys over a short period of 

time is on the order of a day or a week. If a relatively small number of keys are to be 

wrapped under the key-wrapping key, the originator-usage period of the key-wrapping

key could be up to two years. In the case of keys used for only a single message or 

communications session, the cryptoperiod would be limited to a single communication 

session. Except for the latter, a maximum recipient-usage period of three years beyond 

the end of the originator-usage period is recommended.

8. Symmetric RBG keys: 

a. Type Considerations: Symmetric RBG keys are used in deterministic random bit 

generation functions. The approved RBGs in [SP800-90] control key changes (e.g., 

during reseeding). The cryptoperiod consists of only an originator-usage period. 

b. Cryptoperiod: Assuming the use of approved RBGs, the maximum cryptoperiod of 

symmetric RBG keys is determined by the design of the RBG (see [SP800-90]).

9. Symmetric master key: 

a. Type Considerations: A symmetric master key (also called a key-derivation key) may 

be used multiple times to derive other keys using a (one-way) key-derivation function

or method (see Section 8.2.4). Therefore, the cryptoperiod consists of only an 

originator-usage period for this key type. A suitable cryptoperiod depends on the nature 

and use of the keys derived from the master key and on considerations provided earlier 

in Section 5.3. The cryptoperiod of a key derived from a master key could be relatively 

short, e.g., a single use, communication session, or transaction. Alternatively, the 

master key could be used over a longer period of time to derive (or re-derive) multiple 

keys for the same or different purposes. The cryptoperiod of the derived keys depends 

on their use (e.g., as symmetric data-encryption or integrity authentication keys). 

b. Cryptoperiod: An appropriate cryptoperiod for the symmetric master key might be 

one year, depending on its usage environment and the sensitivity/criticality of the 

information protected by the derived keys and the number of keys derived from the 

master key. 

10. Private key-transport key: 

a. Type Considerations: A private key-transport key may be used multiple times to 

decrypt keys. Due to the potential need to decrypt keys some time after they have been 

encrypted for transport, the cryptoperiod of the private key-transport key may be longer 

than the cryptoperiod of the associated public key. The cryptoperiod of the private key 

is the length of time during which any keys encrypted by the corresponding public keytransport key need to be decrypted. 

b. Cryptoperiod: Given 1) the use of approved algorithms and key sizes, 2) the volume 

of information that may be protected by keys encrypted under the corresponding public 

key-transport key, and 3) an expectation that the security of the key-storage and use 
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environment will increase as the sensitivity and/or criticality of the processes for which 

the key provides protection increases; a maximum cryptoperiod of about two years is 

recommended for the private key-transport key. In certain applications (e.g., email), 

where received messages are stored and decrypted at a later time, the cryptoperiod of 

the private key-transport key may exceed the cryptoperiod of the public key-transport

key. 

11. Public key-transport key: 

a. Type Considerations: The cryptoperiod for the public key-transport key is that period 

of time during which the public key may be used to actually apply the encryption 

operation to the keys that will be protected. When the public key has been certified by a 

CA, the cryptoperiod ends when the notAfter date is reached on the last certificate 

issued for the public key. 

Public key-transport keys can be publicly known. As indicated in the private keytransport key discussion, due to the potential need to decrypt keys some time after they 

have been encrypted for transport, the cryptoperiod of the public key-transport key may 

be shorter than that of the corresponding private key.

b. Cryptoperiod: Based on cryptoperiod assumptions for the corresponding private 

keys, a recommendation for the maximum cryptoperiod might be about one to two

years.

12. Symmetric key-agreement key: 

a. Type Considerations: A symmetric key-agreement key may be used multiple times. 

The cryptoperiod of these keys depends on 1) environmental security factors, 2) the 

nature (e.g., types and formats) and volume of keys that are established, and 3) the 

details of the key-agreement algorithms and protocols employed. Note that symmetric 

key-agreement keys may be used to establish symmetric keys (e.g., symmetric data 

encryption keys) or other keying material (e.g., IVs).

b. Cryptoperiod: Given an assumption that the cryptography that employs symmetric 

key-agreement keys 1) employs an approved algorithm and key scheme, 2) the 

cryptographic device meets [FIPS140] requirements, and 3) the risk levels are 

established in conformance to [FIPS199], an appropriate cryptoperiod for the key 

would be one to two years. In certain applications (e.g., email), where received 

messages are stored and decrypted at a later time, the recipient-usage period of the key 

may exceed the originator-usage period.

13. Private static key-agreement key: 

a. Type Considerations: A private static (i.e., long-term) key-agreement key may be 

used multiple times. When a CA certified the corresponding public key, the 

cryptoperiod ends when the notAfter date is reached on the last certificate issued for the 

public key.

As in the case of symmetric key-agreement keys, the cryptoperiod of these keys 

depends on 1) environmental security factors, 2) the nature (e.g., types and formats) 

and volume of keys that are established, and 3) the details of the key-agreement

algorithms and protocols employed. Note that private static key-agreement keys may be 
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used to establish symmetric keys (e.g., key-wrapping keys) or other secret keying 

material.

b. Cryptoperiod: Given an assumption that the cryptography that employs private static 

key-agreement keys 1) employs an approved algorithm and key scheme, 2) the 

cryptographic device meets [FIPS140] requirements, and 3) the risk levels are 

established in conformance to [FIPS199], an appropriate cryptoperiod for the key 

would be one to two years. While the cryptoperiods of the private and public static keyagreement keys are usually the same, in certain applications (e.g., email), where 

received messages are stored and decrypted at a later time, the cryptoperiod of the 

private static key-agreement key may exceed the cryptoperiod of the corresponding 

public static key-agreement key. 

14. Public static key-agreement key: 

a. Type Considerations: The cryptoperiod for a public static (i.e., long-term) keyagreement key is usually the same as the cryptoperiod of the corresponding private 

static key-agreement key. 

b. Cryptoperiod: The cryptoperiod of the public static key-agreement key may be one to 

two years. 

15. Private ephemeral key-agreement key: 

a. Type Considerations: Private ephemeral (i.e., short-term) key-agreement keys are the 

private key elements of asymmetric key pairs that are used in a single transaction to 

establish one or more keys. Private ephemeral key-agreement keys may be used to 

establish symmetric keys (e.g., key-wrapping keys) or other secret keying material.

b. Cryptoperiod: Private ephemeral key-agreement keys are used for a single keyagreement transaction. However, a private ephemeral key may be used multiple times 

to establish the same symmetric key with multiple parties during the same transaction 

(broadcast). The cryptoperiod of a private ephemeral key-agreement key is the duration 

of a single key-agreement transaction. 

16. Public ephemeral key-agreement key: 

a. Type Considerations: Public ephemeral (i.e., short-term) key-agreement keys are the 

public key elements of asymmetric key pairs that are used only once to establish one or 

more keys.

b. Cryptoperiod: Public ephemeral key-agreement keys are used for a single keyagreement transaction. The cryptoperiod of the public ephemeral key-agreement key 

ends immediately after it is used to generate the shared secret. Note that in some cases, 

the cryptoperiod of the public ephemeral key-agreement key may be different for the 

participants in the key-agreement transaction. For example, consider an encrypted 

email application in which the email sender generates an ephemeral key-agreement key 

pair, and then uses the key pair to generate an encryption key that is used to encrypt the 

contents of the email. For the sender, the cryptoperiod of the public key ends when the 

shared secret is generated and the encryption key is derived. However, for the 

encrypted email receiver, the cryptoperiod of the ephemeral public key does not end 

until the shared secret is generated and the decryption key is determined; if the email is 
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not processed immediately upon receipt (e.g., it is decrypted a week later than the email 

was sent), then the cryptoperiod of the ephemeral public key does not end (from the 

perspective of the receiver) until the shared secret is generated that uses that public key.

17. Symmetric authorization key: 

a. Type Considerations: A symmetric authorization key may be used for an extended 

period of time, depending on the resources that are protected and the role of the entity 

authorized for access. For this key type, the originator-usage period and the recipientusage period are the same. Primary considerations in establishing the cryptoperiod for 

symmetric authorization keys include the robustness of the key, the adequacy of the 

cryptographic method, and the adequacy of key-protection mechanisms and procedures. 

b. Cryptoperiod: Given the use of approved algorithms and key sizes, and an 

expectation that the security of the key-storage and use environment will increase as the 

sensitivity and criticality of the authorization processes increases, it is recommended 

that cryptoperiods be no more than two years.

18. Private authorization key: 

a. Type Considerations: A private authorization key may be used for an extended 

period of time, depending on the resources that are protected and the role of the entity 

authorized for access. Primary considerations in establishing the cryptoperiod for 

private authorization keys include the robustness of the key, the adequacy of the 

cryptographic method, and the adequacy of key-protection mechanisms and procedures. 

The cryptoperiod of the private authorization key and its corresponding public key 

shall be the same. 

b. Cryptoperiod: Given the use of approved algorithms and key sizes, and an 

expectation that the security of the key-storage and use environment will increase as the 

sensitivity and criticality of the authorization processes increases, it is recommended 

that cryptoperiods for private authorization keys be no more than two years.

19. Public authorization key: 

a. Type Considerations: A public authorization key is the public element of an 

asymmetric key pair used to verify privileges for an entity that possesses the 

corresponding private key. 

b. Cryptoperiod: The cryptoperiod of the public authorization key shall be the same as 

the private authorization key: no more than two years. 

Table 1 below is a summary of the cryptoperiods that are suggested for each key type. Longer 

or shorter cryptoperiods may be warranted, depending on the application and environment in 

which the keys will be used. However, when assigning a longer cryptoperiod than that 

suggested below, serious consideration should be given to the risks associated with doing so 

(see Section 5.3.1).
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Table 1: Suggested cryptoperiods for key types15

Key Type

Crytoperiod

Originator-Usage 

Period (OUP)

Recipient-Usage 

Period

1. Private Signature Key 1 to 3 years −

2. Public Signature-Verification Key Several years (depends on key size)

3. Symmetric Authentication Key < 2 years < OUP + 3 years

4. Private Authentication Key 1 to 2 years

5. Public Authentication Key 1 to 2 years

6. Symmetric Data Encryption Keys < 2 years < OUP + 3 years

7. Symmetric Key Wrapping Key < 2 years < OUP + 3 years

8. Symmetric RBG Keys See [SP800-90] −

9. Symmetric Master Key About 1 year −

10. Private Key Transport Key < 2 years16

11. Public Key Transport Key 1 to 2 years

12. Symmetric Key Agreement Key 1 to 2 years17

13. Private Static Key Agreement Key 1 to 2 years18

14. Public Static Key Agreement Key 1 to 2 years

15. Private Ephemeral Key Agreement 

Key One key-agreement transaction

16. Public Ephemeral Key Agreement 

Key One key-agreement transaction

 15 In some cases, risk factors affect the cryptoperiod selection (see Section 5.3.1).

16 In certain email applications where received messages are stored and decrypted at a later time, the cryptoperiod 

of the private key-transport key may exceed the cryptoperiod of the public key-transport key.

17 In certain email applications where received messages are stored and decrypted at a later time, the key's 

recipient-usage period key may exceed the originator-usage period.

18 In certain email applications whereby received messages are stored and decrypted at a later time, the 

cryptoperiod of the private static key-agreement key may exceed the cryptoperiod of the public static keyagreement key. 
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Key Type

Crytoperiod

Originator-Usage 

Period (OUP)

Recipient-Usage 

Period

17. Symmetric Authorization Key < 2 years

18. Private Authorization Key < 2 years

19. Public Authorization Key < 2 years

5.3.7 Recommendations for Other Cryptographic or Related Information

Information other than keys does not have well-established cryptoperiods, per se. The 

following recommendations are offered regarding the disposition of this other keying material:

1. Domain parameters remain in effect until changed. 

2. An IV is associated with the information that it helps to protect, and is needed until the 

information in its cryptographically protected form is no longer needed.

3. Shared secrets generated during the execution of key-agreement schemes shall be 

destroyed as soon as they are no longer needed to derive keying material.

4. RBG seeds shall be destroyed immediately after use.

5. Other public information should not be retained longer than needed for cryptographic 

processing.

6. Other secret information shall not be retained longer than necessary.

7. Intermediate results shall be destroyed immediately after use.

5.4 Assurances

When cryptographic keys and domain parameters are stored or distributed, they may pass 

through unprotected environments. In this case, specific assurances are required before the key 

or domain parameters may be used to perform normal cryptographic operations.

5.4.1 Assurance of Integrity (Integrity Protection)

Assurance of integrity shall be obtained prior to using all keying material.

At a minimum, assurance of integrity shall be obtained by verifying that the keying material 

has the appropriate format and came from an authorized source. Additional assurance of 

integrity may be obtained by the proper use of error detection codes, message authentication 

codes, and digital signatures. 

5.4.2 Assurance of Domain Parameter Validity 

Domain parameters are used by discrete log public-key algorithms during the generation of key 

pairs and digital signatures, and during the generation of shared secrets (during the execution 

of a key-agreement scheme) that are subsequently used to derive keying material. Assurance of 

the validity of the domain parameters is important to applications of public-key cryptography 

and shall be obtained prior to using them. 
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Invalid domain parameters could void all intended security for all entities using the domain 

parameters. Methods for obtaining assurance of domain-parameter validity for the DSA and 

ECDSA digital signature algorithms are provided in [SP800-89]. Methods for obtaining 

assurance of domain-parameter validity for finite-field and elliptic-curve discrete-log keyagreement algorithms are provided in [SP800-56A]. 

Note that if a public key is certified by a CA for these algorithms, the CA could obtain this 

assurance during the certification process. Otherwise, the key-pair owner and any relying 

parties are responsible for obtaining the assurance.

5.4.3 Assurance of Public-Key Validity

Assurance of public-key validity shall be obtained on all public keys before using them.

Assurance of public-key validity gives the user confidence that the public key is arithmetically 

correct. This reduces the probability of using weak or corrupted keys. Invalid public keys could 

result in voiding the intended security, including the security of the operation (i.e., digital 

signature, key establishment, or encryption), leaking some or all information from the owner's 

private key, and leaking some or all information about a private key that is combined with an 

invalid public key (as may be done when key agreement or public-key encryption is 

performed). One of several ways to obtain assurance of validity is for an entity to verify certain 

mathematical properties that the public key should have. Another way is to obtain the 

assurance from a trusted third party (e.g., a CA) that the trusted party validated the properties.

Methods of obtaining assurance of public-key validity for the DSA, ECDSA and RSA digital 

signature algorithms are provided in [SP800-89]. Methods for obtaining this assurance for the 

finite-field and elliptic-curve discrete-log key-establishment schemes are provided in [SP800-

56A]. Methods for obtaining assurance of (partial) public-key validity for the RSA keyestablishment schemes are provided in [SP800-56B].

5.4.4 Assurance of Private-Key Possession

Assurance of static (i.e., long-term) private-key possession shall be obtained before the use of 

the corresponding static public key. Assurance of validity shall always be obtained prior to, or 

concurrently with, assurance of possession. Assurance of private-key possession shall be 

obtained by both the owner of the key pair and by other entities that receive the public key of 

that key pair and use it to interact with the owner.

For specific details regarding assurance of the possession of private key-establishment keys, 

see [SP800-56A] and [SP800-56B]; for specific details regarding assurance of the possession 

of private digital-signature keys, see [SP800-89]. Note that for public keys that are certified by 

a CA, the CA could obtain this assurance during the certification process. Otherwise, the 

owner and relying parties are responsible for obtaining the assurance. 

5.5 Compromise of Keys and other Keying Material

Information protected by cryptographic mechanisms is secure only if the algorithms remain 

strong, and the keys have not been compromised. Key compromise occurs when the protective 

mechanisms for the key fail (e.g., the confidentiality, integrity or association of the key to its 

owner fail—see Section 6), and the key can no longer be trusted to provide the required 

security. When a key is compromised, all use of the key to apply cryptographic protection to 

information (e.g., compute a digital signature or encrypt information) shall cease, and the 
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compromised key shall be revoked (see Section 8.3.5). However, the continued use of the key 

under controlled circumstances to remove or verify the protections (e.g., decrypt or verify a 

digital signature) may be warranted, depending on the risks of continued use and an 

organization's Key Management Policy (see [SP800-57, Part 2]). The continued use of a 

compromised key shall be limited to processing already-protected information. In this case, the 

entity that uses the information shall be made fully aware of the dangers involved. Limiting the 

cryptoperiod of the key limits the amount of material that would be compromised (exposed) if 

the key were compromised. Using different keys for different purposes (e.g., different 

applications, as well as different cryptographic mechanisms), as well as limiting the amount of 

information protected by a single key, also achieves this purpose. 

The compromise of a key has the following implications:

1. The unauthorized disclosure of a key means that another entity (an unauthorized entity) 

may know the key and be able to use that key to perform computations requiring the 

use of the key. 

In general, the unauthorized disclosure of a key used to provide confidentiality 

protection19 (i.e., via encryption) means that all information encrypted by that key 

could be determined by unauthorized entities. For example, if a symmetric dataencryption key is compromised, the unauthorized entity might use the key to decrypt 

past or future encrypted information, i.e., the information is no longer confidential 

between the authorized entities. In addition, a compromised key could be used by an 

adversary to encrypt information of the adversary's choosing, thus providing false 

information.

The unauthorized disclosure of a private signature key means that the integrity and nonrepudiation qualities of all data signed by that key are suspect. An unauthorized party in 

possession of the private key could sign false information and make it appear to be 

valid. In cases where it can be shown that the signed data was protected by other 

mechanisms (e.g., physical security) from a time before the compromise, the signature 

may still have some value. For example, if a signed message was received on day 1,

and it was later determined that the private signing key was compromised on day 15, 

the receiver may still have confidence that the message is valid because it was 

maintained in the receiver’s possession before day 15. Note that cryptographic 

timestamping may also provide protection for messages signed before the private 

signature key was compromised. However, the security provided by these other 

mechanisms is now critical to the security of the signature. In addition, the nonrepudiation of the signed message may be questioned, since the private signature key 

may have been disclosed to the message receiver, who then altered the message in 

some way.

The disclosure of a CA’s private signature key means that an adversary can create 

fraudulent certificates and Certificate Revocation Lists (CRLs). 

2. A compromise of the integrity of a key means that the key is incorrect − either that the 

key has been modified (either deliberately or accidentally), or that another key has been 

 19 As opposed to the confidentiality of a key that could, for example, be used as a signing private key.
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substituted; this includes a deletion (non-availability) of the key. The substitution or 

modification of a key used to provide integrity20 calls into question the integrity of all 

information protected by the key. 

3. A compromise of a key’s usage or application association means that the key could be 

used for the wrong purpose (e.g., for key establishment instead of digital signatures) or 

for the wrong application, and could result in the compromise of information protected 

by the key.

4. A compromise of a key’s association with the owner or other entity means that the 

identity of the other entity cannot be assured (i.e., one does not know who the other 

entity really is).

5. A compromise of a key’s association with other information means that there is no 

association at all, or the association is with the wrong “information”. This could cause 

the cryptographic services to fail, information to be lost, or the security of the 

information to be compromised.

Certain protective measures may be taken in order to minimize the likelihood or consequences 

of a key compromise. The following procedures are usually involved:

a. Limiting the amount of time a symmetric or private key is in plaintext form.

b. Preventing humans from viewing plaintext symmetric and private keys.

c. Restricting plaintext symmetric and private keys to physically protected containers. 

This includes key generators, key-transport devices, key loaders, cryptographic 

modules, and key-storage devices.

d. Using integrity checks to ensure that the integrity of a key or its association with other 

data has not been compromised. For example, keys may be wrapped (i.e., encrypted) in 

such a manner that unauthorized modifications to the wrapped key or to the key's 

metadata will be detected.

e. Employing key confirmation (see Section 4.2.5.5) to help ensure that the proper key 

was, in fact, established.

f. Establishing an accountability system that keeps track of each access to symmetric and 

private keys in plaintext form.

g. Providing a cryptographic integrity check on the key (e.g., using a MAC or a digital 

signature).

h. The use of trusted timestamps for signed data.

i. Destroying keys as soon as they are no longer needed.

j. Creating a compromise-recovery plan, especially in the case of the compromise of a CA 

key.

The worst form of key compromise is one that is not detected. Nevertheless, even in this case, 

certain protective measures can be taken. Cryptographic Key Management Systems (CKMSs) 

should be designed to mitigate the negative effects of a key compromise. A CKMS should be 

 20 As opposed to the integrity of a key that could, for example, be used for encryption.
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designed so that the compromise of a single key compromises as little data as possible. For 

example, a single cryptographic key could be used to protect the data of only a single user or a 

limited number of users, rather than a large number of users. Often, systems have alternative 

methods to authenticate communicating entities that do not rely solely on the possession of 

keys. The object is to avoid building a system with catastrophic weaknesses.

A compromise-recovery plan is essential for restoring cryptographic security services in the 

event of a key compromise. A compromise-recovery plan shall be documented and easily 

accessible. The plan may be included in the Key Management Practices Statement (see 

[SP800-57, Part 2]). If not, the Key Management Practices Statement should reference the 

compromise-recovery plan. 

Although compromise recovery is primarily a local action, the entire community that uses the 

system or equipment shares the repercussions. Therefore, compromise-recovery procedures 

should include the community at large. For example, recovery from the compromise of a root 

CA’s private signature key requires that all users of the infrastructure obtain and install a new 

trust anchor certificate. Typically, this involves physical procedures that are expensive to 

implement. To avoid these expensive procedures, elaborate precautions to avoid compromise 

may be justified.

The compromise-recovery plan should contain:

1. The identification of the personnel to notify,

2. The identification of the personnel to perform the recovery actions,

3. The method for obtaining a new key (i.e., re-keying), 

4. An inventory of all cryptographic keys (e.g., the location of all certificates in a system), 

5. The education of all appropriate personnel on the recovery procedures,

6. An identification of all personnel needed to support the recovery procedures,

7. Policies that key-revocation checking be enforced (to minimize the effect of a 

compromise),

8. The monitoring of the re-keying operations (to ensure that all required operations are 

performed for all affected keys), and 

9. Any other recovery procedures.

Other compromise-recovery procedures may include:

a. A physical inspection of the equipment,

b. An identification of all information that may be compromised as a result of the 

incident, 

c. An identification of all signatures that may be invalid, due to the compromise of a 

signing key, and

d. The distribution of new keying material, if required.
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5.6 Guidance for Cryptographic Algorithm and Key-Size Selection

Cryptographic algorithms that provide the security services identified in Section 3 are specified 

in Federal Information Processing Standards (FIPS) and NIST Recommendations. Several of 

these algorithms are defined for several of key sizes. This section provides guidance for the 

selection of appropriate algorithms and key sizes.

This section emphasizes the importance of acquiring cryptographic systems with appropriate 

algorithm and key sizes to provide adequate protection for 1) the expected lifetime of the 

system and 2) any data protected by that system during the expected lifetime of the data.

5.6.1 Comparable Algorithm Strengths

Cryptographic algorithms can provide different “strengths” of security, depending on the 

algorithm and the key size used (when a key is employed). Table 2 gives the current estimates 

for the maximum security strengths that the approved symmetric and asymmetric 

cryptographic algorithms can provide, given keys of a specified length. These estimates were 

made under the assumption that the keys used with those algorithms are generated and handled 

in accordance with specific rules (e.g., the keys are generated using RBGs that were seeded 

with sufficient entropy). However, these rules are often not followed, and the security provided 

to the data protected by those keys may be somewhat less than the security strength estimates 

provided.

Two algorithms are considered to be of comparable strength for the given key sizes (X and Y) 

if the amount of work needed to “break the algorithms” or determine the keys (with the given 

key sizes and sufficient entropy) is approximately the same using a given resource. The 

security strength of an algorithm for a given key size is traditionally described in terms of the 

amount of work it takes to try all keys for a symmetric algorithm with a key size of “X” that 

has no short-cut attacks (i.e., the most efficient attack is to try all possible keys). In this case, 

the best attack is said to be the exhaustion attack. An algorithm that has a Y-bit key, but whose 

estimated maximum security strength is comparable to a symmetric algorithm with an X-bit 

key is said have an “estimated maximum security strength of X bits” or to be able to provide “X

bits of security”. Given a few plaintext blocks and corresponding ciphertext, an algorithm that 

can provide X bits of security would, on average, take 2X-1T units of time to attack, where T is 

the amount of time that is required to perform one encryption of a plaintext value and compare

the result against the corresponding ciphertext value.

Determining the security strength of an algorithm can be nontrivial. For example, consider 

TDEA, which uses three 56-bit keys (K1, K2 and K3). If each of these keys is independently 

generated, then this is called three-key TDEA (3TDEA). However, if K1 and K2 are 

independently generated, and K3 is set equal to K1, then this is called two-key TDEA 

(2TDEA). One might expect that 3TDEA would provide 56 × 3 = 168 bits of strength. 

However, there is an attack on 3TDEA that reduces the strength to the work that would be 

involved in exhausting a 112-bit key. For 2TDEA, if exhaustion were the best attack, then the 

strength of 2TDEA would be 56 × 2 = 112 bits. This appears to be the case if the attacker has 

only a few matched plain and cipher pairs. However, the security strength of 2TDEA decreases 

as the number of matched plaintext/ciphertext pairs increases. If the attacker can obtain 

approximately 240 such pairs and has sufficient memory and computational power, then 

2TDEA can provide an estimated maximum security strength of about 80 bits; if the attacker 
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has 256 plaintext/ciphertext pairs, with significantly more memory and computational power, 

then the estimated maximum security strength would be about 56 bits.

The comparable key-size classes discussed in this section are based on estimates made as of 

the publication of this Recommendation using currently known methods. Advances in 

factoring algorithms, advances in general discrete-logarithm attacks, elliptic-curve discretelogarithm attacks and quantum computing may affect these equivalencies in the future. New or 

improved attacks or technologies may be developed that leave some of the current algorithms 

completely insecure. If quantum attacks become practical, the asymmetric techniques may no 

longer be secure. Periodic reviews will be performed to determine whether the stated 

equivalencies need to be revised (e.g., the key sizes need to be increased) or the algorithms are 

no longer secure.

The use of strong cryptographic algorithms may mitigate security issues other than just bruteforce cryptographic attacks. The algorithms may unintentionally be implemented in a manner 

that leaks small amounts of information about the key. In this case, the larger key may reduce 

the likelihood that this leaked information will eventually compromise the key.

When selecting a block-cipher cryptographic algorithm (e.g., AES or TDEA), the block size 

may also be a factor that should be considered, since the amount of security provided by 

several of the modes defined in [SP800-38] is dependent on the block size. More information 

on this issue is provided in [SP800-38].

Table 2 provides estimated, comparable maximum security strengths for the approved

algorithms and key lengths. 

1. Column 1 indicates the estimated maximum security strength (in bits) provided by the 

algorithms and key sizes in a particular row. Note that the security strength is not 

necessarily the same as the length of the key for the algorithms in the other columns, 

due to attacks on those algorithms that provide computational advantages.

2. Column 2 identifies the symmetric-key algorithms that can provide the security 

strength indicated in column 1, where 2TDEA and 3TDEA are specified in [SP800-67], 

and AES is specified in [FIPS197]. 2TDEA is TDEA with two different keys; 3TDEA 

is TDEA with three different keys.

3. Column 3 indicates the minimum size of the parameters associated with the standards 

that use finite-field cryptography (FFC). Examples of such algorithms include DSA, as 

defined in [FIPS186] for digital signatures, and Diffie-Hellman (DH) and MQV key 

agreement, as defined in [SP800-56A], where L is the size of the public key, and N is 

the size of the private key.

4. Column 4 indicates the value for k (the size of the modulus n) for algorithms based on 

integer-factorization cryptography (IFC). The predominant algorithm of this type is the 

RSA algorithm. RSA is approved in [FIPS186] for digital signatures, and in [SP800-

56B] for key establishment. The value of k is commonly considered to be the key size.

5. Column 5 indicates the range of f (the size of n, where n is the order of the base point 

G) for algorithms based on elliptic-curve cryptography (ECC) that are specified for 

digital signatures in [ANSX9.62] and adopted in [FIPS186], and for key establishment 

as specified in [SP800-56A]. The value of f is commonly considered to be the key size.
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Table 2: Comparable strengths

Security

Strength

Symmetric 

key 

algorithms

FFC

(e.g., DSA, D-H)

IFC

(e.g., RSA)

ECC

(e.g., ECDSA)

≤ 80 2TDEA21

L = 1024

N = 160

k = 1024 f = 160-223

112 3TDEA

L = 2048

N = 224

k = 2048 f = 224-255

128 AES-128

L = 3072

N = 256

k = 3072 f = 256-383

192 AES-192

L = 7680

N = 384

k = 7680 f = 384-511

256 AES-256

L = 15360

N = 512

k = 15360 f = 512+

Note that the 192-bit and 256-bit key strengths identified for the FFC and IFC algorithms 

(shaded in yellow) are not currently included in the NIST standards for interoperability and 

efficiency reasons.

Also, note that algorithm/key-size combinations that have been estimated at a maximum 

security strength of less than 112 bits (shaded in orange above) are no longer approved for 

applying cryptographic protection on Federal government information (e.g., encrypting data or 

generating a digital signature). However, some flexibility is allowed for processing alreadyprotected information at those security strengths (e.g., decrypting encrypted data or verifying 

digital signatures) if the receiving entity accepts the risks associated with doing so. See 

[SP800131A] for more detailed information.

Appropriate hash functions that may be employed will be determined by the algorithm, scheme 

or application in which the hash function is used and by the minimum security-strength to be 

provided. Table 3 lists the approved hash functions specified in [FIPS186] and [FIPS202] that 

can be used to provide each identified security strength for various hash-function applications: 

digital signatures, HMAC, key derivation and random bit generation. 

 21 See the example in the third paragraph of Section 5.6.1.
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Table 3: Hash functions that can be used to provide the targeted security strengths

Note that some security strengths in the table do not indicate a hash function for the 

application; it is always acceptable to use a hash function with a higher estimated maximum 

security strength than that required for the application.

Note that in the case of HMAC, which requires a key, the estimate assumes that a key whose 

length and entropy are at least equal to the security strength is used.

For some applications, a cryptographic key is associated with the application and needs to be 

considered when determining the security strength actually afforded by the application. For 

example, for the generation of digital signatures, the minimum key length for the keys for a 

given security strength is provided in the FFC, IFC and ECC columns of Table 2; while for 

HMAC, the key lengths are discussed in [SP800-107]. 

Note that hash functions and applications providing less than 112 bits of security strength 

(shaded in orange) are no longer approved for applying cryptographic protection on Federal 

government information (e.g., generating a digital signature). However, some flexibility is 

allowed for processing already-protected information at those security strengths (e.g., verifying 

digital signatures), if the receiving entity accepts the risks associated with doing so. See 

[SP800131A] for more detailed information.

 22 Assumes that pre-image resistance is required, rather than collision resistance.

23 The security strength for key-derivation assumes that the shared secret contains sufficient entropy to support the 

desired security strength.

24 The security strength assumes that the random number generator has been provided with adequate entropy to 

support the desired security strength.

25 SHA-1 has been demonstrated to provide less than 80 bits of security for digital signatures, which require 

collision resistance; at the publication of this Recommendation, the security strength against digital signature 

collisions remains the subject of speculation. 

Security 

Strength

Digital Signatures and hash-only 

applications

HMAC22,

Key Derivation Functions23,

Random Number Generation24

≤ 80 SHA-125

112 SHA-224, SHA-512/224, SHA3-224

128 SHA-256, SHA-512/256, SHA3-256 SHA-1 

192 SHA-384, SHA3-384 SHA-224, SHA-512/224

≥ 256 SHA-512, SHA3-512 SHA-256, SHA-512/256, SHA-384, 

SHA-512, SHA3-512
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5.6.2 Defining Appropriate Algorithm Suites 

Many applications require the use of several different cryptographic algorithms. When several 

algorithms can be used to perform the same service, some algorithms are inherently more 

efficient because of their design (e.g., AES has been designed to be more efficient than 

TDEA). 

In many cases, a variety of key sizes may be available for an algorithm. For some of the 

algorithms (e.g., public-key algorithms, such as RSA), the use of larger key sizes than are 

required may impact operations, e.g., larger keys may take longer to generate or longer to 

process the data. However, the use of key sizes that are too small may not provide adequate 

security. 

Table 4 provides general recommendations that may be used to select an appropriate suite of 

algorithms and key sizes for Federal Government unclassified applications to protect sensitive 

data. A schedule for increasing the security strengths for applying cryptographic protection to 

data (e.g., encrypting or digitally signing) is specified in the table. Transition details for 

algorithms, key sizes and applications are provided in [SP800-131A]. The table is organized as 

follows:

1. Column 1 is divided into two sub-columns. The first sub-column indicates the security 

strength to be provided; the second sub-column indicates whether cryptographic 

protection is being applied to data (e.g., encrypted), or whether cryptographically 

protected data is being processed (e.g., decrypted).

2. Columns 2 and 3 indicate the time frames during which the security strength is either 

acceptable, OK for legacy use or disallowed26. 

• “Acceptable” indicates that the algorithm or key length is not known to be insecure.

• “Legacy-use” means that an algorithm or key length may be used because of its use 

in legacy applications (i.e., the algorithm or key length can be used to process 

cryptographically protected data). 

• “Disallowed” means that an algorithm or key length shall not be used for applying 

cryptographic protection. 

Table 4: Security-strength time frames

Security Strength Through 

2030

2031 and 

Beyond

< 112 Applying Disallowed

Processing Legacy-use

112 Applying Acceptable

Disallowed

Processing Legacy use

 26 A fourth category − deprecated − was used in the previous version of this Recommendation, but is not currently 

being used.
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Security Strength Through 

2030

2031 and 

Beyond

128

Applying/Processing

Acceptable Acceptable

192 Acceptable Acceptable

256 Acceptable Acceptable

See [SP800-131A] for specific details and for any exceptions to the general guidance provided 

in Table 4.

If the security life of information extends beyond one time period specified in the table into the 

next time period (the later time period), the algorithms and key sizes specified for the later time 

period shall be used for applying cryptographic protection (e.g., encryption). The following 

examples are provided to clarify the use of the table: 

1. If information is cryptographically protected (e.g., digitally signed) in 2015, and the 

maximum-expected security life of that data is only one year, any of the approved

digital-signature algorithms or key sizes that provide at least 112 bits of security 

strength may be used. 

2. If the information is to be digitally signed in 2025, and the expected security life of the 

data is six years, then an algorithm or key size that provides at least 128 bits of security 

strength is required. 

5.6.3 Using Algorithm Suites

Algorithm suites that combine algorithms with a mixture of estimated maximum security 

strengths is generally discouraged. However, algorithms of different strengths and key sizes 

may be used together for performance, availability or interoperability reasons, provided that 

sufficient protection is provided to the data to be protected. In general, the weakest algorithm 

and key size used to provide cryptographic protection determines the strength of the protection.

A determination of the actual strength of the protection provided for information includes an 

analysis not only of the algorithm(s) and key size(s) used to apply the cryptographic 

protection(s) to the information, but also the details of how the key was generated (e.g., the 

security strength supported by the RBG used during the generation of the key) and how the key 

was handled subsequent to generation (e.g., was the key wrapped by an algorithm with a 

security strength less than the security strength intended for the key's use.

The following is a list of several algorithm combinations and discussions on the security 

implications of the algorithm/key-size combination:

1. When a key-establishment scheme is used to establish keying material for use with one 

or more algorithms (e.g., TDEA, AES, or HMAC), the security strength that can be 

supported by the keying material is determined by the weakest algorithm and key size 

used. For example, if a 224-bit ECC key is used as specified in [SP80056A] to establish 

a 128-bit AES key, no more than 112 bits of security can be provided for any 

information protected by that AES key, since the 224-bit ECC can only provide a 

maximum of 112 bits of security. 
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2. When a hash function and digital signature algorithm are used in combination to 

compute a digital signature, the security strength of the signature is determined by the 

weaker of the two processes. For example, if SHA-256 is used with RSA and a 2048-

bit key, the combination can provide no more than 112 bits of security, because a 2048-

bit RSA key cannot provide more than 112 bits of security strength. 

3. When a random bit generator is used to generate a key for a cryptographic algorithm 

that is intended to provide X bits of security, an approved random bit generator shall

be used that provides at least X bits of security.

If it is determined that a specific level of security is required for the protection of data, then an 

algorithm and key size suite needs to be selected that could provide that level of security (as a 

minimum). For example, if 128 bits of security are required for data that is to be communicated 

and provided with confidentiality protection, and integrity and source authentication, the 

following selection of algorithms and key sizes may be appropriate:

a. Confidentiality: Encrypt the information using AES-128. Other AES key sizes would 

also be appropriate, but performance may be a little slower.

b. Integrity authentication and source authentication: If only one cryptographic operation 

is preferred, use digital signatures. SHA-256 or a larger hash function could be used. 

Select an algorithm for digital signatures from what is available to an application (e.g., 

ECDSA with at least a 256-bit key). If more than one algorithm and key size is 

available, the selection may be based on algorithm performance, memory requirements, 

etc., as long as the minimum requirements are met.

c. Key establishment: Select a key-establishment scheme that is based on the application 

and environment (see [SP80056A] or [SP800-56B]), the availability of an algorithm in 

an implementation, and its performance. Select a key size from Table 2 for an 

algorithm and key size that can provide at least 128 bits of security. For example, if an 

ECC key-agreement scheme is available, use an ECC scheme with at least a 256-bit 

key (the value of f in Table 2). However, the key used for key agreement shall be 

different from the ECDSA key used for digital signatures.

Agencies that procure systems should consider the potential operational lifetime of the system. 

The agencies shall either select algorithms that are expected to be secure during the entire 

system lifetime, or should ensure that the algorithms and key sizes can be readily updated.

5.6.4 Transitioning to New Algorithms and Key Sizes

The estimated time period during which data protected by a specific cryptographic algorithm 

(and key size) remains secure is called the algorithm security lifetime. During this time, the 

algorithm may be used to both apply cryptographic protection (e.g., encrypt data) and to 

process the protected information (e.g., decrypt data); the algorithm is expected to provide 

adequate protection for the protected data during this period. 

Typically, an organization selects the cryptographic services that are needed for a particular 

application. Then, based on the algorithm security lifetime and the security life of the data to 

be protected, an algorithm and key-size suite is selected that is sufficient to meet the

requirements. The organization then establishes a key-management system, including validated

cryptographic products that provide the services required by the application. As an algorithm 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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and/or key-size suite nears the end of its security lifetime, transitioning to a new algorithm and 

key-size suite should be planned. 

When the algorithm or key size is determined to no longer provide the desired protection for 

information (e.g., the algorithm may have been "broken"), any information protected by the 

algorithm or key size is considered to be suspect (e.g., the data may no longer be confidential, 

or the integrity cannot be assured). If the protected data is retained, it should be re-protected 

using an approved algorithm and key size that will protect the information for the remainder 

of its security life. However, it should be assumed that encrypted information could have been 

collected and retained by unauthorized entities (adversaries) for decryption at some later time. 

In addition, the recovered plaintext could be used to attempt a matched plaintext-ciphertext 

attack on the new algorithm. 

When using Tables 2, 3 and 4 to select the appropriate algorithm and key size, it is very 

important to take the expected security life of the data into consideration. As stated earlier, an 

algorithm (and key size) may be used both to apply cryptographic protection to data and 

process the protected data. When the security life of the data is taken into account, 

cryptographic protection should not be applied to data using a given algorithm (and key size) 

if the security life of the data extends beyond the end of the algorithm security lifetime (i.e., 

into the timeframe when the algorithm or key size is disallowed; see Table 4). The period of 

time that an algorithm (and key size) may be used to apply cryptographic protection is called 

the algorithm originator-usage period. The algorithm security life = (the algorithm originatorusage period) + (the security life of the data beyond the algorithm originator-usage period) (see 

Figure 2).

For example, suppose that 3TDEA is to be used to provide confidentiality protection for data 

with a security life of four years. Table 2 indicates that 3TDEA has a maximum security 

strength of 112 bits. Table 4 indicates that an algorithm with a security strength of 112 bits has 

an algorithm security lifetime that extends through 2030 for applying cryptographic protection 

(i.e., encryption, in this case), but not beyond. Since the data has a four-year security life, the 

algorithm originator-usage period must end by December 31, 2026 (rather than 2030) in order 

to ensure that all data protected by 3TDEA is secure during its entire security life (i.e., the 

algorithm could not be used to encrypt data beyond 2026). See Figure 2. After 2026, the 

algorithm could be used to decrypt data for another four years, with the expectation that the 

confidentiality of the data continues to be protected at a security strength of 112 bits. If the 

security life of the data was estimated correctly, the data would no longer need this 

confidentiality protection after 2030. However, if the security life of the data is longer than 

originally expected, then the protection provided after 2030 may be less than required, and 

there is some risk that the confidentiality of the data may be compromised (after 2030); 

accepting the risk associated with the possible compromise is indicated by the “legacy use” 

indication in Table 4.

When initiating cryptographic protections for information, the strongest algorithm and key size 

that is appropriate for providing the protection should be used in order to minimize costly 

transitions. However, it should be noted that selecting some algorithms or key sizes that are 

unnecessarily large might have adverse performance effects (e.g., the algorithm may be 

unacceptably slow).
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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The process of transitioning to a new algorithm or a new key size may be as simple as selecting 

a more secure option in the security suites offered by the current system, or it can be as 

complex as building a whole new system. However, given that it is necessary to develop a new 

algorithm suite for a system, the following issues should be considered.

1. The sensitivity of information and the system lifetime: The sensitivity of the 

information that will need to be protected by the system for the lifetime of the new 

algorithm(s) should be evaluated in order to determine the minimum securityrequirement for the system. Care should be taken not to underestimate the required 

lifetime of the system or the sensitivity of information that it may need to protect. 

Many decisions that were initially considered as temporary or interim decisions

about data sensitivity have since been proven to be inadequate (e.g., the sensitivity 

of the information lasted well beyond its initially expected lifetime). 

2. Algorithm selection: New algorithms should be carefully selected to ensure that 

they meet or exceed the minimum security requirement of the system. In general, it 

is relatively easy to select cryptographic algorithms and key sizes that offer high 

security. However, it is wise for the amateur to consult a cryptographic expert when 

making such decisions. Systems should offer algorithm-suite options that provide 

for future growth. 

3. System design: A new system should be designed to meet the minimum 

performance and security requirements. This is often a difficult task, since 

Figure 2: Algorithm Originator-Usage Period Example
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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performance and security goals may conflict. All aspects of security (e.g., physical 

security, computer security, operational security, and personnel security) are 

involved. If a current system is to be modified to incorporate new algorithms, the 

consequences need to be analyzed. For example, the existing system may require 

significant modifications to accommodate the footprints (e.g., key sizes, block 

sizes, etc.) of the new algorithms. In addition, the security measures (other than the 

cryptographic algorithms) retained from the current system should be reviewed to 

assure that they will continue to be effective in the new system.

4. Pre-implementation evaluation: Strong cryptography may be poorly 

implemented. Therefore, a changeover to new cryptographic techniques should not

be made without an evaluation as to how effective and secure they are in the 

system.

5. Testing: Any system should be tested before it is employed.

6. Training: If the new system requires that new or different tasks (e.g., key 

management procedures) be performed, then the individuals who will perform those 

tasks should be properly trained. Features that are thought to be improvements may 

be viewed as annoyances by an untrained user.

7. System implementation and transition: Care should be taken to implement the 

system as closely as possible to the design. Exceptions should be noted. 

8. Transition: A transition plan should be developed and followed so that the 

changeover from the old to the new system runs as smoothly as possible.

9. Post-implementation evaluation: The system should be evaluated to verify that 

the implemented system meets the minimum security requirements.

5.6.5 Security Strength Reduction

At some time, the security strength provided by an algorithm or key may be reduced or lost 

completely. For example, the algorithm or key length used may no longer offer adequate 

security because of improvements in computational capability or cryptanalysis. In this case, 

applying protection to “new” information can be performed using stronger algorithms or keys. 

However, information that was previously protected using these now-inadequate algorithms 

and keys may no longer be secure. This information may include other keys, or other sensitive 

data protected by the keys. A reduction in the security strength provided by an algorithm or 

key has the following implications:

• Encrypted information: The security of encrypted information that was available at any 

time to unauthorized entities in its encrypted form should be considered suspect. For 

example, keys that were transmitted in encrypted form (e.g., using a key-wrapping key 

or key-transport key and an algorithm or key length that is later broken) may need to be 

considered as compromised, since an adversary could have saved the encrypted form of 

the keys for later decryption in case methods for breaking the algorithm would 

eventually be found (see Section 5.5 for a discussion of key compromise). Even if the 

transmitted, encrypted information is subsequently re-encrypted for storage using a 

different key or algorithm, the information may already be compromised because of the 

weakness of the transmission algorithm or key. 
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Encrypted information that was not “exposed” in this manner (e.g., not transmitted) 

may still be secure, even though the encryption algorithm or key length no longer 

provides adequate protection. For example, if the encrypted form of the keys and the 

information protected by those keys was never transmitted, then the information may 

still be confidential. 

The lessons to be learned are that an encryption mechanism used for information that 

will be available to unauthorized entities in its encrypted form (e.g., via transmission) 

should provide a high level of security protection, and the use of each key should be 

limited (i.e., the cryptoperiod should be short) so that a compromised key cannot be 

used to reveal very much information. If the algorithm itself is broken27, an adversary is 

forced to perform more work when each key is used to encrypt a very limited amount 

of information in order to decrypt all of the information. See Section 5.3.6 for a 

discussion about cryptoperiods.

• Digital signatures on stored data28: Digital signatures may be computed on data prior to 

transmission and subsequent storage. In this case, both the signed data and the digital 

signature would be stored. If the security strength of the signature is later reduced (e.g., 

because of a break of the algorithm), the signature may still be valid if the stored data 

and its associated digital signature have been adequately protected from modification

since a time prior to the reduction in strength (e.g., by applying a digital signature using 

a stronger algorithm or key). See Section 5.5, item 1 for further discussion. Storage 

capabilities are being developed that employ cryptographic timestamps to store 

digitally signed data beyond the normal security life of the original signature 

mechanism or its keys.

• Symmetric authentication codes on stored data29: Like digital signatures, symmetric 

authentication codes (i.e., MACs) may be computed on data prior to transmission and 

subsequent storage. If the received data and authentication code are stored as received, 

and the security strength of the authentication algorithm or key is later reduced (e.g., 

because of a break of the algorithm), the authentication code may still be valid if the 

stored data and its associated authentication code have been adequately protected from 

modification since a time prior to the reduction in strength (e.g., by applying another 

authentication code using a stronger algorithm or key). See Section 5.5, item 1 for 

further discussion. Storage capabilities are being developed that employ cryptographic 

timestamps to store authenticated data beyond the normal security life of the original 

authentication mechanism or its keys.

 27 It is easier to recover a key than exhaustive search. 

28 Digital signatures on data that is transmitted, but not stored are not considered, as their value is considered to be 

short-lived, e.g., the digital signature was intended to be used to detect errors introduced only during transmission.

29 Symmetric authentication codes on data that is transmitted, but not stored are not considered, as their value is 

considered to be short-lived.
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6 Protection Requirements for Cryptographic Information

This section gives guidance on the types of protection required for keying material. 

Cryptographic keying material is defined as the cryptographic key and associated information 

required to use the key (i.e., the metadata). The specific information varies, depending on the 

type of key. The cryptographic keying material must be protected in order for the security 

services to be “meaningful.” A FIPS 140-validated cryptographic module may provide much

of the protection needed; however, whenever the keying material exists external to a [FIPS140]

cryptographic module, additional protection is required. The type of protection needed depends 

on the type of key and the security service for which the key is used. [SP800-152] provides 

guidance for Federal Cryptographic Key Management Systems (FCKMSs) on the protection of 

keys and metadata when outside a FIPS 140-validated cryptographic module, as well as other 

key management factors to be addressed. 

6.1 Protection and Assurance Requirements

Keying material should be (operationally) available as long as the associated cryptographic 

service is required. Keys may be maintained within a cryptographic module while they are 

being actively used, or they may be stored externally (provided that proper protection is 

afforded) and recalled as needed. Some keys may need to be archived if required beyond the 

key’s originator-usage period (see Section 5.3.5 for a discussion of the originator-usage 

period).

The following protections and assurances may be required for the keying material. 

Integrity protection shall be provided for all keying material. Integrity protection always 

involves checking the source and format of received keying material (see Section 5.4.1). 

When the key exists within a validated cryptographic module, appropriate integrity 

protection is provided when the cryptographic module conforms to [FIPS140], at a security 

level that is consistent with the [FIPS 199] impact level associated with the data to be 

protected by the key (see [SP800-152]). When a key is available outside a cryptographic 

module, integrity protection shall be provided by appropriate cryptographic integrity

mechanisms (e.g. cryptographic checksums, cryptographic hash functions, MACs, and 

digital signatures), non-cryptographic integrity mechanisms (e.g. CRCs, parity checks, etc.) 

(see Appendix A), or physical protection mechanisms. Guidance for the selection of 

appropriate integrity mechanisms is given in Sections 6.2.1.2 and 6.2.2.2.

Confidentiality protection for all symmetric and private keys shall be provided. Public keys 

generally do not require confidentiality protection. When the symmetric or private key 

exists within a validated cryptographic module, appropriate confidentiality protection is 

provided when the cryptographic module conforms to [FIPS140], at a security level that is 

consistent with the [FIPS199] impact level associated with the data to be protected by the 

key (see [SP800-152]). When a symmetric or private key is available outside a

cryptographic module, confidentiality protection shall be provided either by encryption 

(e.g., key wrapping) at an appropriate security strength (see [SP800-152]), by the use of 

separate key components (see Section 6.2.1.3) or by controlling access to the key via 

physical means (e.g. storing the keying material in a safe with limited access). The security 

and operational impact of specific confidentiality mechanisms varies. Guidance for the 

selection of appropriate confidentiality mechanisms is given in Sections 6.2.1.3 and 6.2.2.3.
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Association protection shall be provided for a cryptographic security service by ensuring 

that the correct keying material is used with the correct data in the correct application or 

equipment. Guidance for the selection of appropriate association protection is given in 

Sections 6.2.1.4 and 6.2.2.4.

Assurance of domain-parameter and public-key validity provides confidence that the 

parameters and keys are arithmetically correct (see Sections 5.4.2 and 5.4.3). Guidance for 

the selection of appropriate assurance mechanisms is given in [SP800-56A] and [SP800-

89], as well as in this document.

Assurance of private key possession provides assurance that the owner of a public key 

actually possesses the corresponding private key (see Section 5.4.4). 

The period of protection for cryptographic keys, associated key information, and cryptographic 

parameters (e.g. initialization vectors) depends on the type of key, the associated cryptographic 

service, and the length of time for which the cryptographic service is required. The period of 

protection includes the cryptoperiod of the key (see Section 5.3). The period of protection is 

not necessarily the same for integrity as it is for confidentiality. Integrity protection may only 

be required until a key is no longer used (but not yet destroyed), but confidentiality protection 

may be required until the key is actually destroyed.

6.1.1 Summary of Protection and Assurance Requirements for Cryptographic Keys

Table 5 provides a summary of the protection requirements for keys during distribution and 

storage. Methods for providing the necessary protection are discussed in Section 6.2.

Guide to Table 5:

a. Column 1 (Key Type) identifies the key types.

b. Column 2 (Security Service) indicates the type of security service that is provided by 

the key in conjunction with a cryptographic technique. In some cases, the word 

"support" is used in this column. This means that the associated key is used to support 

the primary cryptographic services of confidentiality, integrity authentication, and 

source authentication. For example, a key-agreement key may support a confidentiality 

service by establishing the key used to provide confidentiality; an RBG key supports 

the use of cryptography because it is used to provide the random values for generating 

the keys to be used to cryptographically protect information.

c. Column 3 (Security Protection) indicates the type of protection required for the key 

(i.e., integrity and confidentiality). 

d. Column 4 (Association Protection) indicates the types of associations that need to be 

protected for that key, such as associating the key with the usage or application, the 

authorized communications participants or other indicated information. The association 

with domain parameters applies only to algorithms where they are used. 

e. Column 5 (Assurances Required) indicates whether assurance of public-key validity 

and/or assurance of private-key possession needs to be obtained as defined in [SP800-

56A], [SP800-56B], [SP800-89] and this Recommendation. Assurance of public-key

validity provides a degree of confidence that a key is arithmetically correct. See Section 

5.4.3 for further details. Assurance of private-key possession provides a degree of 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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confidence that the entity providing a public key actually possessed the associated 

private key at some time. See Section 5.4.4 for further details. 

f. Column 6 (Period of Protection) indicates the length of time that the integrity and/or 

confidentiality of the key needs to be maintained (see Section 5.3). Symmetric keys and 

private keys shall be destroyed at the end of their period of protection (see Sections 

8.3.4 and 9.3).

Table 5: Protection requirements for cryptographic keys

Key Type Security 

Service

Security 

Protection

Association 

Protection

Assurances 

Required

Period of 

Protection

Private 

signature key

Source 

authentication

Integrity

authentication

Support nonrepudiation

Integrity30

Confidentiality

Usage or application

Domain parameters

(when used)

Public signatureverification key

Possession From generation 

until the end of the 

cryptoperiod

Public 

signatureverification

key

Source 

authentication

Integrity

authentication

Support nonrepudiation

Integrity Usage or application

Key pair owner

Domain parameters

(when used)

Private signature key 

Signed data

Validity From generation 

until no protected 

data needs to be 

verified

Symmetric 

authentication 

key

Source 

authentication

Integrity

authentication

Integrity

Confidentiality

Usage or application

Other authorized 

entities

Authenticated data

From generation 

until no protected 

data needs to be 

verified

Private 

authentication 

key

Source 

authentication

Integrity 

authentication

Integrity

Confidentiality

Usage or application

Public 

authentication key

Domain parameters

(when used)

Possession From generation 

until the end of the 

cryptoperiod

Public 

authentication 

key

Source 

authentication

Integrity 

authentication

Integrity Usage or application

Key pair owner

Authenticated data

Private 

authentication key

Domain parameters

(when used)

Validity From generation 

until no protected 

data needs to be 

authenticated

 30 Integrity protection can be provided by a variety of means. See Sections 6.2.1.2 and 6.2.2.2.
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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Key Type Security 

Service

Security 

Protection

Association 

Protection

Assurances 

Required

Period of 

Protection

Symmetric 

dataencryption/

decryption key

Confidentiality Integrity 

Confidentiality

Usage or application

Other authorized 

entities

Plaintext/Encrypted 

data

From generation 

until the end of the 

lifetime of the data 

or the end of the 

cryptoperiod, 

whichever comes 

later

Symmetric 

key-wrapping

key

Support Integrity

Confidentiality

Usage or application

Other authorized 

entities

Encrypted keys

From generation 

until the end of the 

cryptoperiod or until 

no wrapped keys 

require protection, 

whichever is later.

Symmetric 

RBG keys

Support Integrity

Confidentiality

Usage or application From generation 

until replaced

Symmetric 

master key

Support Integrity

Confidentiality

Usage or application

Other authorized 

entities

Derived keys

From generation 

until the end of the 

cryptoperiod or the 

end of the lifetime 

of the derived keys, 

whichever is later.

Private keytransport keySupport Integrity

Confidentiality

Usage or application

Encrypted keys

Public key-transport

key

Possession From generation 

until the end of the 

period of protection 

for all transported 

keys

Public keytransport keySupport Integrity Usage or application

Key pair owner

Private key-transport

key

Validity From generation 

until the end of the 

cryptoperiod

Symmetric 

key-agreement

key

Support Integrity

Confidentiality

Usage or application

Other authorized 

entities

From generation 

until the end of the 

cryptoperiod or until 

no longer needed to 

determine a key, 

whichever is later

Private static 

key-agreement

key

Support Integrity

Confidentiality

Usage or application

Domain parameters

(when used)

Public static keyagreement key

Possession From generation 

until the end of the 

cryptoperiod or until 

no longer needed to 

determine a key, 

whichever is later
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Key Type Security 

Service

Security 

Protection

Association 

Protection

Assurances 

Required

Period of 

Protection

Public static 

key-agreement

key

Support Integrity Usage or application

Key pair owner

Domain parameters

(when used)

Private static keyagreement key

Validity From generation 

until the end of the 

cryptoperiod or until 

no longer needed to 

determine a key, 

whichever is later

Private 

ephemeral 

key-agreement

key

Support Integrity

Confidentiality

Usage or application 

Public ephemeral 

key-agreement key

Domain parameters

(when used)

From generation 

until the end of the 

key-agreement

process

After the end of the 

process, the key 

shall be destroyed

Public 

ephemeral 

key-agreement

key

Support Integrity31 Key pair owner

Private ephemeral 

key-agreement key

Usage or application

Domain parameters

(when used)

Validity From generation 

until the keyagreement process is 

complete

Symmetric 

authorization 

keys

Authorization Integrity

Confidentiality

Usage or application

Other authorized 

entities

From generation 

until the end of the 

cryptoperiod of the 

key

Private 

authorization 

key

Authorization Integrity

Confidentiality

Usage or application

Public authorization 

key 

Domain parameters

(when used)

Possession From generation 

until the end of the 

cryptoperiod of the 

key

Public 

authorization 

key

Authorization Integrity Usage or application

Key pair owner

Private authorization 

key 

Domain parameters 

(when used)

Validity From generation 

until the end of the 

cryptoperiod of the 

key 

 31 The confidentiality of public ephemeral key-agreement keys may not be protected during transmission; 

however, the key-agreement protocols may be designed to detect unauthorized substitutions and modifications of 

the transmitted public ephemeral keys. In this case, the protocols form the data integrity mechanism.
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6.1.2 Summary of Protection Requirements for Other Cryptographic or Related 

Information

Table 6 provides a summary of the protection requirements for other cryptographic information 

during distribution and storage. Mechanisms for providing the necessary protection are 

discussed in Section 6.2.

Guide to Table 6:

a. Column 1 (Cryptographic Information Type) identifies the type of cryptographic 

information.

b. Column 2 (Security Service) indicates the type of security service provided by the 

cryptographic information.

c. Column 3 (Security Protection) indicates the type of security protection for the 

cryptographic information. 

d. Column 4 (Association Protection) indicates the relevant types of associations for each 

type of cryptographic information. 

e. Column 5 (Assurance of Domain Parameter Validity) indicates the cryptographic 

information for which assurance shall be obtained as defined in [SP800-56A] and 

[SP800-89] and in Section 5.4 of this Recommendation. Assurance of domainparameter validity gives confidence that domain parameters are arithmetically correct.

f. Column 6 (Period of Protection) indicates the length of time that the integrity and/or 

confidentiality of the cryptographic information needs to be maintained. The 

cryptographic information shall be destroyed at the end of the period of protection (see 

Section 8.3.4).

Table 6: Protection requirements for other cryptographic or related material

Crypto. 

Information

Type

Security 

Service

Security 

Protection

Association 

Protection

Assurance 

of Domain 

Parameter 

Validity

Period of Protection

Domain 

parameters

Depends on the 

key assoc. with 

the parameters

Integrity Usage or application

Private and public 

keys

Yes From generation until 

no longer needed to 

generate keys or 

verify signatures

Initialization 

vectors

Depends on the 

algorithm

Integrity32 Protected data From generation until 

no longer needed to 

process the protected 

data

 32 IVs are not generally protected during transmission; however, the decryption system may be designed to detect 

or minimize the effect of unauthorized substitutions and modifications to transmitted IVs. In this case the 

decryption system is the data-integrity mechanism.
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Crypto. 

Information

Type

Security 

Service

Security 

Protection

Association 

Protection

Assurance 

of Domain 

Parameter 

Validity

Period of Protection

Shared secrets Support Confidentiality

Integrity

From generation until 

the end of the 

transaction. 

The shared secret 

shall be destroyed at 

the end of the period 

of protection

RBG Seeds Support Confidentiality 

Integrity

Usage or application Used once and 

destroyed

immediately after use

Other public 

information

Support Integrity Usage or application

Other authorized 

entities

Data processed 

using the nonce

From generation until 

no longer needed to 

process data using 

the public 

information

Other secret 

information

Support Confidentiality

Integrity

Usage or application

Other authorized 

entities

Data processed 

using the secret 

information

From generation until 

no longer needed to 

process data using 

the secret 

information

Intermediate 

results

Support Confidentiality

Integrity

Usage or application From generation until 

no longer needed and 

the intermediate 

results are destroyed

Key-control 

information 

(e.g., IDs, 

purpose)

Support Integrity Key From generation until 

the associated key is 

destroyed

Random 

number

Support Integrity

Confidentiality 

(depends on 

usage)

From generation until 

no longer needed, 

and the random 

number is destroyed

Password Source 

authentication; 

Key derivation

Integrity

Confidentiality

Usage or application

Owning entity

From generation until 

replaced or no longer 

needed to 

authenticate the 

entity or to derive 

keys

Audit 

information

Support Integrity

Access 

authorization

Audited events

Key control 

information

From generation until 

no longer needed
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6.2 Protection Mechanisms

During the lifetime of cryptographic information, the information is either “in transit” (e.g., is 

in the process of being manually distributed or distributed using automated protocols to the 

authorized communication participants for use by those entities), “at rest” (e.g., the information 

is in storage) or “in use.” In all cases, the keying material shall be protected in accordance with 

Section 6.1.

For keys that are in use, the keys shall reside (and be used) within appropriate cryptographic 

modules; note that a key being in use does not preclude that key from also being 

simultaneously in transit and/or in storage.

While in transit or in storage, the choice of protection mechanisms may vary. Although several 

methods of protection are provided in the following subsections, not all methods provide equal 

security. The method should be carefully selected. In addition, the mechanisms prescribed do 

not, by themselves, guarantee protection. The implementation and the associated key 

management need to provide adequate security to prevent any feasible attack from being 

successful.

6.2.1 Protection Mechanisms for Cryptographic Information in Transit

Cryptographic information in transit may be keying material that is being distributed in order 

to obtain a cryptographic service (e.g., establish a key that will be used to provide 

confidentiality) (see Section 8.1.5), cryptographic information that is being backed up or 

archived for possible use or recovery in the future (see Sections 8.2.2 and 8.3.1), or is in the 

process of being recovered (see Sections 8.2.2.2, 8.3.1 and Appendix B). This may be 

accomplished manually (i.e., via a trusted courier), in an automated fashion (i.e., using 

automated communication protocols) or by some combination of manual and automated 

methods. For some protocols, the protections are provided by the protocol; in other cases, the 

protection of the keying material is provided directly to the keying material (e.g., the keying 

material is encrypted prior to transmission for decryption only by the receiving party). It is the 

responsibility of the originating entity to apply protection mechanisms, and the responsibility 

of the recipient to undo or check the mechanisms used.

6.2.1.1 Availability

Since communications may be garbled, intentionally altered, or destroyed, the availability of 

cryptographic information after transit cannot be assured using cryptographic methods. 

However, availability can be supported by redundant or multiple channels, store and forward 

systems (deleting by the sender only after confirmation of receipt), error correction codes, and 

other non-cryptographic mechanisms. 

Communication systems should incorporate non-cryptographic mechanisms to ensure the

availability of transmitted cryptographic information after it has been successfully received, 

rather than relying on retransmission by the original sender for future availability

6.2.1.2 Integrity

Integrity protection involves both the prevention and detection of modifications to information. 

When modifications are detected, measures may be taken to restore the information to its 

unaltered form. Cryptographic mechanisms are often used to detect unauthorized 
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modifications. The integrity of cryptographic information during transit shall be protected 

using one or more of the following mechanisms:

1. Manual method (physical protection is provided):

(a) An integrity mechanism (e.g., a CRC, MAC or digital signature) is used on the 

information, and the resulting code is provided to the recipient for subsequent 

verification. Note: A CRC may be used instead of a MAC or digital signature, since 

the physical protection is only intended to protect against intentional modifications.

-OR-

(b) The keying material is used to perform the intended cryptographic operation. If the 

received information does not conform to the expected format, or the data is 

inconsistent in the context of the application, then the keying material may have 

been corrupted.

2. Automated distribution via communication protocols (provided by the user or by the 

communication protocol):

(a) An approved cryptographic integrity mechanism (e.g., a MAC or digital signature) 

is used on the information, and the resulting code is provided to the recipient for 

subsequent verification. Note that a CRC is not approved for this purpose. The 

integrity mechanism may be applied only to the cryptographic information, or may 

be applied to an entire message.

-OR-

(b) The keying material is used to perform the intended cryptographic operation. If the 

use of the keying material produces incorrect results, or the data is inconsistent in 

the context of the application, then the received keying material may have been 

corrupted.

The response to the detection of an integrity failure will vary, depending on the specific 

environment. Improper error handling can allow attacks (e.g., side channel attacks). A security 

policy (see [SP800-57, Part 2]) should define the response to such an event. For example, if an 

error is detected in the received information, and the receiver requires that the information is 

entirely correct (e.g., the receiver cannot proceed when the information is in error), then:

a. The information should not be used, 

b. The recipient may request that the information be resent (retransmissions should be 

limited to a predetermined maximum number of times), and

c. Information related to the incident should be stored in an audit log to later identify the 

source of the error.

6.2.1.3 Confidentiality

Keying material may require confidentiality protection during transit. If confidentiality 

protection is required, the keying material shall be protected using one or more of the 

following mechanisms:

1. Manual method: 
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(a) The keying material is encrypted (e.g., wrapped) using an approved technique that 

provides protection at a security strength that meets or exceeds the security strength 

required of the keying material.

-OR-

(b) The keying material is separated into key components, with each key component 

being generated at a security strength that meets or exceeds the security strength 

required of the keying material. Each key component is handled, using splitknowledge procedures (see Sections 8.1.5.2.1 and 8.1.5.2.2.1), so that no single 

individual can acquire access to all key components.

-OR-

(c) Appropriate physical and procedural protection is provided (e.g., by using a trusted 

courier).

2. Automated distribution via communication protocols: The keying material is encrypted

(e.g., wrapped) using an approved technique that provides protection at the security 

strength that meets or exceeds the security strength required of the keying material.

6.2.1.4 Association with Usage or Application

The association of keying material with its usage or application shall be either specifically 

identified during the distribution process or be implicitly defined by the use of the application. 

See Section 6.2.3 for a discussion of the metadata associated with keys.

6.2.1.5 Association with Other Entities

The association of keying material with the appropriate entity (e.g., the entity that shares the 

keying material) shall be either specifically identified during the distribution process (e.g., 

using public-key certificates) or be implicitly defined by the use of the application. See Section 

6.2.3 for a discussion of the metadata associated with keys.

6.2.1.6 Association with Other Related Information

Any association with other related information (e.g., domain parameters, the 

encryption/decryption key or IVs) shall be either specifically identified during the distribution 

process or be implicitly defined by the use of the application. See Section 6.2.3 for a discussion 

of the metadata associated with the other related information.

6.2.2 Protection Mechanisms for Information in Storage

Cryptographic information may be at rest in some device or storage media. This may include 

copies of the information that is also in transit or in use. Information-at-rest (i.e., stored 

information, including information contained within a cryptographic module) shall be 

protected in accordance with Section 6.1. A variety of protection mechanisms may be used.

The cryptographic information may be stored so as to be immediately available to an 

application (e.g., on a local hard disk or a server); this would be typical for keying material 

stored within a cryptographic module or in immediately accessible storage (e.g., on a local 

hard drive). The keying material may also be stored in electronic form on a removable media 

(e.g., a CD-ROM), in a remotely accessible location, or in hard copy form and placed in a safe; 

this would be typical for backup or archive storage.
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6.2.2.1 Availability

Cryptographic information may need to be readily available for as long as data is protected by 

the information. A common method for providing this protection is to make one or more copies 

of the cryptographic information and store them in separate locations. During a key’s 

cryptoperiod, keying material requiring long-term availability should be stored in both normal 

operational storage (see Section 8.2.1) and in backup storage (see Section 8.2.2.1). 

Cryptographic information that is retained after the end of a key’s cryptoperiod should be 

placed in archive storage (see Section 8.3.1). This Recommendation does not preclude the use 

of the same storage media for both backup and archive storage. 

Specifics on the long-term availability requirement for each key type are addressed for backup 

storage in Section 8.2.2.1, and for archive storage in Section 8.3.1.

The recovery of this cryptographic information for use in replacing cryptographic information 

that is lost (e.g., from normal storage), or in performing cryptographic operations after the end 

of a key’s cryptoperiod is discussed in Sections 8.2.2.2 (recovery during normal operations) 

and 8.3.1 (recovery from archive storage), and in Appendix B.

Even though the primary focus of this section is to provide assurance of the availability of 

cryptographic information, there is at least one example where denying the availability of this 

information may be desired, namely when sanitizing large volumes of information that have 

been encrypted. In this case, cryptographic sanitization (i.e., destroying the key used to decrypt 

the information) is suggested (see [SP 800-88]).

6.2.2.2 Integrity

Integrity protection is concerned with ensuring that the information is correct. Absolute 

protection against modification is not possible. The best that can be done is to use reasonable 

measures to prevent modifications, to use methods to detect any modifications that occur (with 

a very high probability), and to restore the information to its original content when 

unauthorized modifications have been detected. 

All cryptographic information requires integrity protection. Integrity protection shall be 

provided by physical mechanisms, cryptographic mechanisms or both.

Physical mechanisms include the use of:

1. A validated cryptographic module or operating system that limits access to the stored 

information,

2. A computer system or media that is not connected to other systems, and

3. A physically secure environment with appropriate access controls that is outside a 

computer system (e.g., in a safe with limited access).

Cryptographic mechanisms include the use of:

a. An approved cryptographic integrity mechanism (e.g., a MAC or digital signature) that 

is computed on the information and is later used to verify the integrity of the stored 

information, and 
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b. Performing the intended cryptographic operation; this assumes that the correct result is 

easily determined. If the received information is incorrect, it is possible that the keying 

material may have been corrupted.

In order to restore the cryptographic information when an error is detected, one or more copies 

of the information should be maintained in physically separate locations (i.e., in backup or 

archive storage; see Sections 8.2.2.1 and 8.3.1). The integrity of each copy should be 

periodically checked.

6.2.2.3 Confidentiality

One of the following mechanisms shall be used to provide confidentiality for private or secret 

keying material in storage:

1. Encryption (or key wrapping) with an approved algorithm in a [FIPS140]

cryptographic module; the encryption shall use an approved technique that 

provides protection at the security strength that meets or exceeds the security 

strength required of the keying material. 

-OR2. Physical protection provided by a [FIPS140] cryptographic module, at a security 

level that is consistent with the [FIPS199] impact level associated with the data to 

be protected by the key (see [SP800-152]). 

-OR3. Physical protection provided by secure storage with controlled access (e.g., a safe 

or protected area).

6.2.2.4 Association with Usage or Application

Cryptographic information is used with a given cryptographic mechanism (e.g., digital 

signatures or a key establishment scheme) or with a particular application. Protection shall be 

provided to ensure that the information is not used incorrectly (e.g., not only must the usage or 

application be associated with the keying material, but the integrity of this association must be 

maintained). This protection can be provided by separating the cryptographic information from 

that of other mechanisms or applications, or by the use of appropriate metadata associated with

the information. Section 6.2.3 addresses the metadata associated with cryptographic 

information.

6.2.2.5 Association with the Other Entities

Some cryptographic information needs to be correctly associated with another entity (e.g., the 

key source), and the integrity of this association shall be maintained. For example, a 

symmetric (secret) key used for the encryption of information, or the computation of a MAC 

needs to be associated with the other entity(ies) that share(s) the key. Public keys need to be 

correctly associated (e.g., cryptographically bound) with the owner of the key pair (e.g., using 

public-key certificates). 

The cryptographic information shall retain its association during storage by separating the 

information by “entity” or application, or by using appropriate metadata for the information.

Section 6.2.3 addresses the metadata used for cryptographic information.
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6.2.2.6 Association with Other Related Information

An association may need to be maintained between protected information and the keying 

material that is used to protect that information. In addition, keys may require association with 

other keying material (see Section 6.2.1.6).

Storing the information together or providing some linkage or pointer between the information

satisfies the association requirement. Often, the linkage between a key and the information it 

protects is accomplished by providing an identifier for a key, storing the identifier with the key 

in the key’s metadata, and storing the key’s identifier with the protected information. The 

association shall be maintained for as long as the protected information needs to be processed.

Section 6.2.3 addresses the use of metadata for cryptographic information.

6.2.3 Metadata Associated with Cryptographic Information

Metadata may be used with cryptographic information to define the use of that information or 

to provide a linkage between cryptographic information.

6.2.3.1 Metadata for Keys

Metadata is used to provide information about the key, including its parameters, or the 

intended use of a key, and as such, contains the key’s control information. Different 

applications may require different metadata elements for the same key type, and different 

metadata elements may be required for different key types. It is the responsibility of an 

implementer to select suitable metadata elements for keys. When metadata is used, the 

metadata should accompany a key (i.e., the metadata is typically stored or transmitted with a 

key). Some examples of metadata elements are:

1. Key identifier;

2. Information identifying associated keys (e.g., the association between a public and 

private key);

3. Identity of the key’s owner or the sharing entity(ies);

4. Cryptoperiod (e.g., the start and end dates);

5. Key type (e.g., a signing private key, encryption key, or master key);

6. Application (e.g., purchasing or email);

7. Sensitivity of the information protected by the key;

8. Counter33;

9. Domain parameters (e.g., the domain parameters used by DSA or ECDSA, or a pointer 

to them);

10. Key state (e.g., pre-activation, active or destroyed);

11. Key status/history (e.g., distributed or revoked (with the revocation reason)); 

12. Key-wrapping key identifier and the algorithm used for wrapping;

 33 Used to detect the playback of a previously transmitted key package.
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13. Integrity-protection mechanism (e.g., the key and algorithm used to provide 

cryptographic protection, and the protection code (e.g., the MAC or digital signature)); 

and

14. Other information (e.g., the length of the key, any protection requirements, who has 

access rights to the key or additional conditions for use).

[SP800-152] provides additional information about the use of metadata, including guidance 

about protecting its integrity and association with the related key.

6.2.3.2 Metadata for Related Cryptographic Information

Cryptographic information other than keying material may need metadata to “point to” the 

keying material that was used to provide the cryptographic protection for the information. The 

metadata may also contain other related cryptographic information. When metadata is used, the 

metadata should accompany the information (i.e., the metadata is typically stored or 

transmitted with the information) and contain some subset of the following:

1. The type of information (e.g., domain parameters);

2. The source of the information (e.g., the entity that sent the information);

3. The application for using the key (e.g., purchasing or email);

4. Other associated cryptographic information (e.g., a key, MAC or hash value); and

5. Any other information (e.g., who has access rights). 
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7 Key States and Transitions

A key may pass through several states between its generation and its destruction. Figure 3

depicts an example of the key states that a key could assume and the transitions among them.

Figure 3: Key state and transition example.

A key is used differently, depending upon its state in the key’s lifecycle. Key states are defined 

from a system point-of-view, as opposed to the point-of-view of a single cryptographic 

module. The following sections discuss the states that an operational or backed-up key may 

assume, along with transitions to other states, as shown in Figure 3. Additional states may be 

applicable for some systems (e.g., a destroyed compromised state, which was depicted in the 

example provided in a previous version of this Recommendation), and some of the identified

states may not be needed for other systems (e.g., if keys are to be activated immediately after 

generation, the pre-activation state may not be needed, or a decision could be made that the 

suspended state will not be used). 
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Transitioning between states often requires recording the event. Suitable places for such 

recordings are audit logs and the key's metadata (see Section 6.2.3.1). [SP800-152] also 

discusses the logging of these events.

The following sections discuss the example provided in Figure 3.

7.1 Pre-activation State 

The key has been generated, but has not been authorized for use. In this state, the key may only 

be used to perform proof-of-possession (Section 8.1.5.1.1.2) or key confirmation (Section 

4.2.5.5). Other than for proof-of-possession or key-confirmation purposes, a key shall not be 

used to apply cryptographic protection to information (e.g., encrypt or sign information to be 

transmitted or stored) or to process cryptographically protected information (e.g., decrypt 

ciphertext or verify a digital signature) while in this state.

Transition 1: A key enters the pre-activation state immediately upon generation. 

Transition 2: If a key is in the pre-activation state, and it has been determined that the key 

will not be needed in the future, the key shall transition directly from the preactivation state to the destroyed state. 

In the case of asymmetric keys, both keys of the key pair shall transition to the 

destroyed state.

The date and time of the transition shall be recorded.

Transition 3: When a key is in the pre-activation state, and the integrity of the key or the 

confidentiality of a key requiring confidentiality protection becomes suspect, 

then the key shall transition from the pre-activation state to the compromised 

state.

In the case of asymmetric keys, both keys of the key pair shall transition to the 

compromised state.

The date and time of the transition shall be recorded. If the key is known by 

multiple entities, a revocation notice shall be generated. 

Transition 4: Keys shall transition from the pre-activation state to the active state when the 

key becomes available for use. This transition may occur upon reaching an 

activation date or may occur because of an external event. In the case where 

keys are generated for immediate use, this transition occurs immediately after 

entering the pre-activation state. 

For asymmetric keys associated with a certificate, both keys of the key pair 

become active upon the notBefore date in the first certificate issued for the 

public key of the key pair.

The date and time of the transition should be recorded.

This transition marks the beginning of the cryptoperiod of a symmetric key or 

both keys of an asymmetric key pair (see Section 5.3).
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7.2 Active State

The key may be used to cryptographically protect information (e.g., encrypt plaintext or 

generate a digital signature), to cryptographically process previously protected information 

(e.g., decrypt ciphertext or verify a digital signature) or both. When a key is active, it may be 

designated for protection only, processing only, or both protection and processing, depending 

on its type. For example, private signature keys and public key-transport keys are implicitly 

designated for only applying protection; public signature-verification keys and private keytransport keys are designated for processing only. A symmetric data-encryption key may be 

used to encrypt data during its originator-usage period and decrypt the encrypted data during 

its recipient-usage period (see Section 5.3.5).

Transition 5: Several key types transition directly from the active state to the destroyed state 

if no compromise has been determined and either the key's cryptoperiod has 

been reached or the key has been replaced.

Private signature keys and private authentication keys shall transition to the 

destroyed state at the end of their respective originator-usage periods (e.g., 

when the notAfter dates are reached on the last certificate issued for the 

corresponding public keys). Note that the corresponding public keys transition

to the deactivated state at this time; see transition 8.

A symmetric RBG key shall transition to the destroyed state when replaced by a

new key or when the RBG will no longer be used.

Symmetric master keys and symmetric authorization keys shall transition to the 

destroyed state at the end of their respective originator-usage periods34.

Private ephemeral key-agreement keys shall transition to the destroyed state 

immediately after use (see [SP800-56A]). The corresponding public ephemeral 

key-agreement keys should transition to the destroyed state when the 

corresponding private keys are destroyed35.

A private authorization key shall transition to the destroyed state at the end of 

its cryptoperiod (e,g., when the notAfter dates is reached on the last certificate 

issued for the corresponding public key). A public authorization key should

transition to the destroyed state when the corresponding private key is 

destroyed36.

The date and time of the transition shall be recorded.

Transition 6: A key or key pair shall transition from the active state to the compromised state 

when the integrity of the key or the confidentiality of a key requiring 

confidentiality protection becomes suspect. In this case, the key or key pair 

shall be revoked.

 34 Recall that the recipient-usage periods of symmetric key-agreement keys and symmetric authorization keys are 

the same as their originator-usage periods (see Section 5.6).

35 Recall that the cryptoperiods of the private and public authentication keys are the same (see Section 5.6). 

36 Recall that the cryptoperiods of the private and public authorization keys are the same (see Section 5.6). 
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In the case of asymmetric key pairs, the compromise pertains explicitly to the 

private key of the key pair, but both keys shall transition to the compromised

state at the same time. For example, when a private signature key or private 

key-transport key is either compromised or suspected of being compromised, 

the corresponding public key also needs to transition to the compromised state.

The date and time of the transition shall be recorded. If the key is known by 

multiple entities, a revocation notice shall be generated.

Transition 7: A key or key pair shall transition from the active state to the suspended state if, 

for some reason, the key is not to be used for a period of time. For example, a 

key may be suspended because the entity associated with the key is on a leave 

of absence. 

In the case of asymmetric keys, both keys of the key pair shall transition to the 

suspended state at the same time.

Symmetric RBG keys shall transition to the compromised state and be replaced, 

rather than suspended.

The date, time and reason for the suspension shall be recorded. If the key or key 

pair is known by multiple entities, a notification indicating the suspension and 

reason shall be generated. 

Transition 8: A key or key pair in the active state shall transition to the deactivated state 

when it is no longer to be used to apply cryptographic protection to data. The 

transition to the deactivated state may be because a symmetric key was replaced 

(see Section 8.2.3), because the end of the originator-usage period has been 

reached (see Sections 5.3.4 and 5.3.5) or because the key or key pair was 

revoked for reasons other than a compromise (e.g., the key's owner is no longer 

authorized to use the key). 

Symmetric authentication keys, symmetric data encryption/decryption keys, 

symmetric key-agreement keys and key wrapping keys transition to the 

deactivated state at the end of the key's originator-usage period. 

Public signature verification keys, public authentication keys, and private/public 

static key-agreement key pairs, transition to the deactivated state at the end of 

the originator-usage period for the corresponding private key (e.g., when the 

notAfter date is reached on the last certificate issued for the public key). Public 

ephemeral key-agreement keys and public authorization keys transition to the 

deactivated state if they have not been destroyed when the corresponding 

private keys were destroyed (see transition 5).

A private and public key-transport key pair transitions to the deactivated state 

when the notAfter date is reached on the last certificate issued for the public 

key. 

The date and time of the transition should be recorded.
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7.3 Suspended State

The use of a key or key pair may be suspended for several possible reasons; in the case of 

asymmetric key pairs, both the public and private keys shall be suspended at the same time. 

One reason for a suspension might be a possible key compromise, and the suspension has been 

issued to allow time to investigate the situation. Another reason might be that the entity that 

owns a digital signature key pair is not available (e.g., is on an extended leave of absence); 

signatures purportedly signed during the suspension time would be invalid.

A suspended key or key pair may be restored to an active state at a later time or may be 

deactivated or destroyed, or may transition to the compromised state. 

A suspended key shall not be used to apply cryptographic protection (e.g., encrypt plaintext or 

generate a digital signature). However, a suspended key could be used to process information 

that was protected prior to the suspension (e.g., decrypt ciphertext or verify a digital signature), 

but the recipient must accept the risk in doing so (e.g., the recipient must understand the reason 

and implications of the suspension). For example, if the reason for the suspension is because of 

a suspected compromise, it may not be prudent to verify signatures using the public key unless 

the key pair is subsequently reactivated. Information for which protection is known to be 

applied during the suspension period shall not be processed until leaving the suspended state, 

at which time its processing depends on the new state.

Transition 9: Several key types transition from the suspended state to the destroyed state if no 

compromise has been determined.

Private signature keys and private authentication keys in the suspended state 

shall transition to the destroyed state at the end of their originator-usage periods 

(e.g., when the notAfter dates are reached on the last certificate issued for the 

corresponding public keys). Note that the corresponding public keys transition 

to the deactivated state at this time (see transition 12).

Symmetric master keys and symmetric authorization keys in the suspended state 

shall transition to the destroyed state at the end of their originator-usage 

periods37.

Private authorization keys in the suspended state shall transition to the 

destroyed state at the end of their originator-usage periods (i.e., when the 

notAfter dates are reached on the last certificate issued for the corresponding 

public keys). Public authorization keys should transition to the destroyed state 

when the corresponding private keys are destroyed38.

The date and time of the transition shall be recorded.

Transition 10: A key or key pair in the suspended state shall transition to the active state when 

the reason for the suspension no longer exists, and the end of the originatorusage period has not been reached.

 37 Recall that the recipient-usage periods of symmetric key-agreement keys and symmetric authorization keys are 

the same as their originator-usage periods (see Section 5.3.6).

38 Recall that the cryptoperiods of the private and public authorization keys are the same (see Section 5.6). 
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In the case of symmetric keys, the transition needs to be made before the end of 

the key's originator-usage period. 

For asymmetric keys, the transition needs to be made, for example, before the 

notAfter date on the last certificate issued for the public key. In this case, both 

the private and public key shall transition at the same time.

The date and time of the transition should be recorded.

Transition 11: A key or key pair in the suspended state shall transition to the compromised 

state when the integrity of the key or the confidentiality of a key requiring 

confidentiality protection becomes suspect or is confirmed. In this case, the key 

or key pair shall be revoked.

In the case of asymmetric key pairs, both the public and private keys shall be 

transition at the same time.

The date and time of the transition shall be recorded. If the key is known by 

multiple entities, a revocation notice shall be generated.

Transition 12: Several key types transition from the suspended state to the deactivated state if 

no compromise has been determined and the suspension is no longer required.

Symmetric authentication keys, symmetric data encryption/decryption keys, and 

symmetric key-wrapping keys shall transition to the deactivated state when the 

ends of their originator-usage periods have been reached.

Public signature verification keys, public authentication keys, and private/public 

static key-agreement key pairs39 transition to the deactivated state at the end of 

the private key's originator-usage period (e.g., when the notAfter date is reached 

on the last certificate issued for the public key). Public ephemeral keyagreement keys and public authorization keys transition to the deactivated state 

if they have not been destroyed when the corresponding private keys were 

destroyed (see transition 9).

A private/public key-transport key pair transitions to the deactivated state at the 

end of the key pair's cryptoperiod (e.g., when the notAfter date is reached on the 

last certificate issued for the public key). 

The date and time of the transition should be recorded.

7.4 Deactivated State

Keys in the deactivated state shall not be used to apply cryptographic protection, but in some 

cases, may be used to process cryptographically protected information. If the key has been 

revoked (i.e., for reasons other than a compromise), then the key may continue to be used for 

 39 In the case of public ephemeral key-agreement keys, the cryptoperiod ends at the same time as that of the 

corresponding private ephemeral key-agreement key (which transitioned to the destroyed state after use (see 

transition 5), However, there is no actual requirement to destroy the public key immediately, so it is listed here as 

transitioning to the deactivated state, rather than the destroyed state. However, transitioning directly to the 

destroyed state would also be acceptable.
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processing. Note that keys retrieved from an archive can be considered to be in the deactivated 

state unless compromised.

• Public signature verification keys may be used to verify the digital signatures generated 

before the end of the corresponding private key's originator-usage period (e.g., before 

the notAfter date in the last certificate for the public key).

• Symmetric authentication keys, symmetric data encryption keys and symmetric keywrapping keys may be used to process cryptographically protected information until the 

end of the recipient-usage period is reached, provided that the protection was applied 

during the key's originator-usage period.

• Public authentication keys may be used to authenticate processes performed before the 

end of the corresponding private key's originator-usage period (e.g., before the notAfter

date in the last certificate for the public key).

• Private key-transport keys may be used to decrypt keys that were encrypted using the 

corresponding public key before the end of the public key's originator-usage period 

(e.g., before the notAfter date in the last certificate for the public key).

• Symmetric key-agreement keys may be used to determine the agreed-upon key, 

assuming that sufficient information is available.

• Private/public static key-agreement keys may be used to regenerate agreed-upon keys 

that were created before the end of the key pair's cryptoperiod (e.g., before the notAfter

date in the last certificate for the public key, assuming that sufficient information is 

available for the key-agreement scheme used).

• Public ephemeral key-agreement keys may be used to regenerate agreed-upon keys 

(assuming that sufficient information is available for the key-agreement scheme used).

• Public authorization keys shall not be used.

Keys in the deactivated state may transition to either the compromised or destroyed state at 

some point in time.

Transition 13: A key shall transition from the deactivated state to the compromised state when 

the integrity of a key or the confidentiality of a key requiring confidentiality 

protection becomes suspect. In this case, the key or key pair shall be revoked.

The date, time and reason for the transition shall be recorded. If the key is 

known by multiple entities, a revocation notice shall be generated.

Transition 14: A key in the deactivated state should transition to the destroyed state as soon as 

it is no longer needed. 

The date, time and reason for the transition shall be recorded.

Note that keys retrieved from an archive may be in the deactivated state.

7.5 Compromised State

Generally, keys are compromised when they are released to or determined by an unauthorized 

entity. A compromised key shall not be used to apply cryptographic protection to information. 

However, in some cases, a compromised key or a public key that corresponds to a 
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compromised private key of a key pair may be used to process cryptographically protected 

information. For example, a signature may be verified to determine the integrity of signed data 

if its signature has been physically protected since a time before the compromise occurred. 

This processing shall be done only under very highly controlled conditions, where the users of 

the information are fully aware of the possible consequences. 

Note that keys retrieved from an archive may be in the compromised state.

Transition 15: A compromised key should transition to the destroyed state when its use will no 

longer be allowed or needed. 

The date and time of the transition shall be recorded.

7.6 Destroyed State

The key has been destroyed as specified in Section 8.3.4. Even though the key no longer exists 

when in this state, certain key metadata (e.g., key state transition history, key name, type, and 

cryptoperiod) may be retained for audit purposes (see Section 8.4).

It is possible that a compromise of the destroyed key could be determined after the key has 

been destroyed. In this case, the compromise should be recorded.
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8 Key-Management Phases and Functions

The cryptographic key-management lifecycle can be divided into four phases. During each 

phase, the keys are in certain specific key states as discussed in Section 7. In addition, within 

each phase, certain key-management functions are typically performed. These functions are 

necessary for the management of the keys and their associated metadata.

Key-management information is called metadata. The metadata required for key management 

might include the identity of a person or system associated with that key or the types of 

information that person is authorized to access. Metadata is used by applications to select the 

appropriate cryptographic key(s) for a particular service. While the metadata does not appear in 

cryptographic algorithms, it is crucial to the implementation of applications and application 

protocols. 

The four phases of key management are:

1. Pre-operational phase: The keying material is not yet available for normal 

cryptographic operations. Keys may not yet be generated, or are in the pre-activation 

state. System or enterprise attributes are 

established during this phase, as well.

2. Operational phase: The keying material 

is available and in normal use. Keys are 

in the active or suspended state. Keys in 

the active state may be designated as 

protect only, process only, or protect and 

process; keys in the suspended state can 

be used for processing only.

3. Post-operational phase: The keying 

material is no longer in normal use, but 

access to the keying material is possible,

and the keying material may be used for 

processing. Keys are in the deactivated or 

compromised states. Keys in the postoperational phase may be in an archive 

(see Section 8.3.1) when not processing 

data.

4. Destroyed phase: Keys are no longer 

available. Records of their existence may 

or may not have been deleted. Keys are in 

the destroyed states. Although the keys 

themselves are destroyed, the key 

metadata (e.g., key name, type, 

cryptoperiod, and usage period) may be 

retained (see Section 8.4).

A flow diagram for the key management phases 

is presented in Figure 4. Seven phase transitions Figure 4: Key management phases.
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are identified in the diagram. A key shall not be able to transfer back to any previous phase.

Transition 1: A key is in the pre-operational phase upon generation (pre-activation state).

Transition 2: If keys are produced, but never used, they may be destroyed by transitioning 

from the pre-operational phase directly to the destroyed phase.

Transition 3: When a key in the pre-operational phase is compromised, it transitions to the 

post-operational phase (compromised state).

Transition 4: After the required key metadata has been established, keying material has 

been generated, and the metadata is associated with the key during the pre-operational 

phase, the key is ready to be used by applications and transitions to the operational 

phase at the appropriate time.

Transition 5: When a key in the operational phase is compromised, it transitions to the 

post-operational phase (compromised state).

Transition 6: When keys are no longer required for normal use (i.e., the end of the 

cryptoperiod has been reached and the key is no longer “active”), but access to those 

keys needs to be maintained, the key transitions to the post-operational phase.

Transition 7: Some applications will require that access be preserved for a period of time, 

and then the keying 

material may be 

destroyed. When it is 

clear that a key in the 

post-operational phase 

is no longer needed, it 

may transition to the

destroyed phase.

The combination of key states 

and key phases is illustrated in 

Figure 5. 

The following subsections 

discuss the functions that are 

performed in each phase of key 

management. A keymanagement system may not 

have all identified functions, 

since some functions may not 

be appropriate. In some cases, 

one or more functions may be 

combined, or the functions may 

be performed in a different 

order. For example, a system 

may omit the functions of the 

post-operational phase if keys 

are immediately destroyed when they are no longer used to apply cryptographic protection or 

Figure 5: Key management states and phases.
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are compromised. In this case, keys would move from the operational phase directly to the 

destroyed phase.

8.1 Pre-operational Phase

During the pre-operational phase of key management, keying material is not yet available for 

normal cryptographic operations.

8.1.1 User Registration Function

During user registration, an entity interacts with a registration authority to become an 

authorized member of a security domain. In this phase, a user identifier or device name may be 

established to identify the member during future transactions. In particular, security 

infrastructures may associate the identification information with the entity’s keys (see Sections 

8.1.5 and 8.1.6). The entity may also establish various information during the registration 

function, such as email addresses, or role and authorization information. As with identity 

information, this information may be associated with the entity’s keys by the infrastructure to 

support secure application-level security services.

Since applications will depend upon the identity established during this process, it is crucial 

that the registration authority establish appropriate procedures for the validation of identity. 

Identity may be established through an in-person appearance at a registration authority, or may 

be established entirely out-of-band. Human entities are usually required to provide credentials 

(e.g., an identification card or birth certificate), while system entities are vouched for by those 

individuals responsible for system operation. The strength (or weakness) of a security 

infrastructure will often depend upon the identification process. [FIPS201] and [SP800-63] 

address requirements for establishing identity.

User and key registration (see Section 8.1.6) may be performed separately, or in concert. If 

performed separately, the user registration process will generally establish a secret value (e.g., 

a password, PIN, or HMAC key); the secret value may be used to authenticate the user's 

identity during the key registration step. If performed in concert, the user establishes an 

identity and performs key registration in the same process, so the secret value is not required. 

8.1.2 System Initialization Function

System initialization involves setting up or configuring a system for secure operation. This 

may include algorithm preferences, the identification of trusted parties, and the definition of 

domain-parameter policies and any trusted parameters (e.g., recognized certificate policies).

8.1.3 User Initialization Function

User initialization consists of an entity initializing its cryptographic application (e.g., installing 

and initializing software or hardware). This involves the use or installation (see Section 8.1.4) 

of the initial keying material that may be obtained during user registration. Examples include 

the installation of a key at a CA, trust parameters, policies, trusted parties, and algorithm 

preferences.

8.1.4 Keying-Material Installation Function 

The security of keying-material installation is crucial to the security of a system. For this 

function, keying material is installed for operational use within an entity’s software, hardware, 

system, application, cryptographic module, or device using a variety of techniques. Keying 
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material is installed during initial set up, when new keying material is added to the existing 

keying material, and when existing keying material is replaced (e.g., via re-keying or key 

derivation − see Sections 8.2.3 and 8.2.4).

The process for the initial installation of keying material (e.g., by manual entry, electronic key 

loader, or a vendor during manufacture) shall include the protection of the keying material 

during entry into a software/hardware/system/application/device/cryptographic module, taking 

into account the requirements of [FIPS140] and its differing requirements for the different

levels of protection, and include any additional procedures that may be required.

Many applications or systems are provided by the manufacturer with keying material that is 

used to test that the newly installed application/system is functioning properly. This test keying 

material shall not be used operationally.

8.1.5 Key Establishment Function

Key establishment involves the generation and distribution, or the agreement of keying 

material for communication between entities. All keys shall be generated within a FIPS 140-

validated cryptographic module or obtained from another source approved by the U.S. 

Government for the protection of national security information. During the key-establishment

process, some of the keying material may be in transit (i.e., the keying material is being 

manually distributed or is being distributed using automated protocols). Other keying material 

may be retained locally. In either case, the keying material shall be protected in accordance 

with Section 6.

An entity may be an individual (person), organization, device or process. When keying 

material is generated by an entity for its own use, one or more of the appropriate protection 

mechanisms for stored information in Section 6.2.2 shall be used. 

Keying material that is distributed between entities, or among an entity and its sub-entities

(e.g., various individuals, devices or processes within an organization), shall be protected 

during distribution using one or more of the appropriate protection mechanisms specified in 

Section 6.2.1. Any keying material that is not distributed (e.g., the private key of a key pair, or 

one's own copy of a symmetric key) or keying material that is received and subsequently stored 

shall be protected using one or more of the appropriate protection mechanisms specified in 

Section 6.2.2.

[SP800-133] discusses the generation of keying material.

8.1.5.1 Generation and Distribution of Asymmetric Key Pairs

Key pairs shall be generated in accordance with the mathematical specifications of the 

appropriate approved FIPS or NIST Recommendation. 

A static key pair shall be generated by the entity that “owns” the key pair (i.e., the entity that 

uses the private key in the cryptographic computations), by a facility that distributes the key 

pair in accordance with Section 8.1.5.1.3, or by the user and facility in a cooperative process. 

When generated by the entity that owns the key pair, a signing private key shall not be 

distributed to other entities. In the case of a public signature-verification key and its associated 

private key, the owner should generate the keying material, rather than any other entity 

generating the keying material for that owner; this will facilitate the support for nonrepudiation. However, when the owner is an organization, it is acceptable to distribute the 
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keying material to the organization's sub-entities (e.g., employees or devices); in this case, the 

organization is the true owner, and the sub-entities represent the owner.

Ephemeral keys are often used for key establishment (see [SP800-56A]). They are generated 

for each new key-establishment transaction (e.g., unique to each message or session) by the 

owner.

The generated key pairs shall be protected in accordance with Section 6.1.1.

8.1.5.1.1 Distribution of Static Public Keys

Static public keys are relatively long-lived and are typically used for several executions of an 

algorithm. The distribution of the public key should provide assurance to the receiver of the 

public key that the true owner of the key is known (i.e., the claimed owner is the actual owner); 

this requirement may be disregarded if anonymity is acceptable. However, the strength of the 

overall architecture and trust in the validity of the protected data depends, in large part, on the 

assurance of the public-key owner’s identity.

In addition, the distribution of the public key shall provide assurance to the receiver that:

1. The purpose/usage of the key is known (e.g., for RSA digital signatures or ellipticcurve key agreement),

2. Any parameters associated with the public key are known (e.g., domain parameters), 

3. The public key is valid (e.g., the public key satisfies the required arithmetical 

properties), and

4. The owner actually possesses the corresponding private key. 

8.1.5.1.1.1 Distribution of a Trust Anchor's Public Key in a PKI

The public key of a trusted Certification Authority is the foundation for all PKI-based security 

services; the trusted CA is considered to be a trust anchor. The trust anchor's public key is not a 

secret, but the authenticity of that public key is the crucial assumption for PKI. Trust anchor

public keys may be obtained through many different mechanisms, providing different levels of 

assurance. The types of mechanisms that are provided may depend on the role of the user in the 

infrastructure. A user that is only acting as a “relying party” – that is, a user that does not have 

keys registered with the infrastructure – may use different mechanisms than a user that 

possesses keys registered by the infrastructure. 

Trust anchor public keys are frequently distributed as “self-signed” X.509 certificates, that is, 

certificates that are signed by the private key corresponding to the public key in the certificate. 

Note that, while this document refers to a trusted CA as the “trust anchor” and its certificate as 

the “trust anchor certificate,” many other documents use the term “trust anchor” to refer to both 

the trusted CA and the CA’s certificate.

Trust anchor certificates are often embedded within an application and distributed with the 

application. For example, the installation of a new web browser typically includes the 

installation or replacement of the user’s list of trust anchor certificates. Operating systems are 

often shipped with “code signing” trust anchor certificates. The user relies upon the 

authenticity of the software distribution mechanism to ensure that only valid trust anchor

certificates are installed during installation or replacement. However, in some cases other 

applications may install trust anchor certificates in web browsers. 
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Trust anchor certificates in web browsers are used for several purposes, including the 

validation of S/MIME e-mail certificates and web server certificates for “secure websites” that 

use the TLS protocol to authenticate the web server and provide confidentiality. Users who 

visit a “secure” website that has a certificate not issued by a trust anchor CA may be given an 

opportunity to accept that certificate, either for a single session or permanently. Relying users 

should be cautious about accepting certificates from unknown Certification Authorities 

so that they do not, in effect, inadvertently add new permanent trust anchor certificates

that are really not trustworthy.

Warning: Roaming users should be aware that they are implicitly trusting all software on the 

host systems that they use. They should have concerns about trust anchor certificates used by 

web browsers when they use systems in kiosks, libraries, Internet cafes, or hotels, as well as

systems provided by conference organizers to access “secure websites.” The user has had no 

control over the trust anchor certificates installed in the host system, and therefore the user is 

relying upon the host systems to have made good, sensible decisions about which trust anchor

certificates are allowed; relying parties are not participants in trust anchor certificate selection 

when the trust anchor certificates are pre-installed prior to software distribution, and may have 

had no part in decisions about which trust anchor certificates are installed thereafter. The user 

should be aware that he is trusting the software distribution mechanism to avoid the installation 

of malicious code. Extending this trust to cover trust anchor certificates for a given application 

may be reasonable, and allows the relying party to obtain trust anchor certificates without any 

additional procedures. 

When a user registers keys with an infrastructure, additional mechanisms are usually available. 

The user interacts securely with the infrastructure to register its keys (e.g., to obtain 

certificates), and these interactions may be extended to provide trust anchor information in the 

form of a trust anchor certificate. This allows the user to establish trust anchor certificates with 

approximately the same assurance that the infrastructure has in the user’s keys. In the case of a 

PKI:

1. The initial distribution of a trust anchor certificate should be performed in conjunction 

with the presentation of a requesting entity’s public key to a registration authority (RA) 

or CA during the certificate request process. In general, the trust anchor's public key, 

associated parameters, key use, and assurance of possession are conveyed as a selfsigned X.509 public-key certificate. In this case, the certificate has been digitally 

signed by the private key that corresponds to the public key within the certificate. 

While the parameters and assurance of possession may be conveyed in the self-signed 

certificate, the identity associated with the trust anchor certificate and other information 

cannot be verified from the self-signed certificate itself (see item 2 below). 

2. The trusted process used to convey a requesting entity's public key and assurances to 

the RA or CA shall also be used to protect the trust anchor's certificate that is conveyed 

to the requesting entity. In cases where the requesting entity appears in person, the trust 

anchor's certificate may be provided at that time. If a secret value has been established 

during user registration (see Section 8.1.1), the trust anchor’s certificate may be 

supplied, along with the requesting entity’s certificate. 
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8.1.5.1.1.2 Submission to a Registration Authority or Certification Authority

Public keys may be provided to a Certification Authority (CA) or to a registration authority 

(RA) for subsequent certification by a CA. During this process, the RA or CA shall obtain the 

assurances listed in Section 8.1.5.1.1 from the owner of the key or an authorized representative 

(e.g., the firewall administrator), including the owner’s identity. 

In general, the owner of the key is identified in terms of an identifier established during user 

registration (see Section 8.1.1). The key owner identifies the appropriate uses for the key, 

along with any required parameters. In cases where anonymous ownership of the public key is 

acceptable, the owner or the registration authority determines a pseudonym to be used as the 

identifier. The identifier shall be unique for the naming authority40.

Proof of Possession (POP) is a mechanism that is commonly used by a CA to obtain assurance 

of private-key possession during key registration. In this case, the proof shall be provided by 

the reputed owner of the key pair. Without assurance of possession, it would be possible for the 

CA to bind the public key to the wrong entity. 

The (reputed) owner should provide POP by performing operations with the private key that 

satisfy the indicated key use. For example, if a key pair is intended for RSA digital signature 

generation, the CA may provide information to be signed using the owner's private key. If the 

CA can correctly verify the signature using the corresponding public key, then the owner has 

established POP. However, when a key pair is intended to support key establishment (i.e., 

either key agreement or key transport), POP may also be afforded by using the private key to 

digitally sign the certificate request (although this is not the preferred method). The private 

key-establishment key (i.e., the private key-agreement or private key-transport key) shall not

be used to perform signature operations after certificate issuance.

As with user registration, the strength of the security infrastructure depends upon the methods 

used for distributing the key to an RA or CA. There are many different methods, each 

appropriate for some range of applications. Some examples of common methods are:

1. The public key and the information identified in Section 8.1.5.1.1 are provided in

person by the public-key owner in person, or by an authorized representative of the 

public-key owner.

2. The identity of the public-key owner or an authorized representative of the public-key 

owner (i.e., a person, organization, device or process) is established at the RA or CA in 

person during user registration. Unique, unpredictable information (e.g., an 

authenticator or cryptographic key) is provided at this time by the RA or CA to the 

owner or authorized representative as a secret value. The public key and the 

information identified in Section 8.1.5.1.1 are provided to the RA or CA using a 

communication protocol protected by the secret value. The secret value should be 

destroyed by the key owner as specified in Section 8.3.4 upon receiving confirmation 

that the certificate has been successfully generated. The RA or CA may maintain this 

 40 The naming authority is the entity responsible for the allocation and distribution of domain names, ensuring that 

the names are unique within the domain. A naming authority is often restricted to a particular level of domains, 

such as .com, ,net or .edu.
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secret value for auditing purposes, but the RA or CA should not accept further use of 

the secret value to prove identity. 

When a specific list of public-key owners are pre-authorized to register keys, identifiers 

may be assigned without the owners being present. In this case, it is critical to protect 

the secret values from disclosure, and the procedures shall demonstrate that the chain 

of custody was maintained. The lifetime of the secret values should be limited, but 

shall allow for the public-key owner to appear at the RA or CA, to generate his keys, 

and to provide the public key (under the secret value’s protection) to the RA or CA. 

Since it may take some time for the public-key owner to appear at the RA or CA, a two 

or three-week lifetime for the secret value is probably reasonable.

When public-key owners are not pre-authorized, the RA or CA shall determine the 

identifier in the user’s presence. In this case, the time limit may be much more 

restrictive, since the public-key owner need only generate his keys and provide the 

public key to the CA or RA. In this case, a 24-hour lifetime for the secret value would 

be reasonable.

3. The identity of the public-key owner is established at the RA or CA using a previous 

determination of the public-key owner’s identity. This is accomplished by “chaining” a 

new public-key certificate request to a previously certified digital-signature key pair. 

For example, the request for a new public-key certificate is signed by the owner of the 

new public key to be certified. The private signature key used to sign the request 

should correspond to a public signature-verification key that is certified by the same 

CA that will certify the new public key. The request contains the new public key and 

any key-related information (e.g., the key use and the key's parameters). In addition, the 

CA shall obtain assurance of public-key validity and assurance that the owner 

possesses the corresponding private key. 

4. The public key, key use, parameters, validity assurance information, and assurance of 

possession are provided to the RA or CA, along with a claimed identity. The RA or CA 

delegates the verification of the public-key owner’s identity to another trusted process 

(e.g., an examination of the public-key owner’s identity by the U.S. Postal Service 

when delivering registered mail containing the requested certificate). Upon receiving a 

request for certification, the RA or CA generates and sends unique, unpredictable 

information (e.g., an authenticator or cryptographic key) to the requestor using a trusted 

process (e.g., registered mail sent via the U.S. Postal Service). The trusted process 

assures that the identity of the requestor is verified prior to delivery of the information 

provided by the RA or CA. The owner uses this information to prove that the trusted 

process succeeded, and the RA or CA subsequently delivers the certificate to the 

owner. The unique, unpredictable information should be destroyed by the key owner as 

specified in Section 8.3.4 upon receiving confirmation that the certificate has been 

successfully generated. (The RA or CA may maintain this information for auditing 

purposes, but should not accept further use of the unique identifier to prove identity.) 

In cases involving an RA, upon receipt of all information from the requesting entity (i.e., the 

owner of the new public key), the RA forwards the relevant information to a CA for 

certification. The RA and CA, in combination, shall perform any validation or other checks 

required for the algorithm with which the public key will be used (e.g., public-key validation) 
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prior to issuing a certificate. The CA should indicate the checks or validations that have been 

performed (e.g., in the certificate, or in the certificate policy or certification practice 

statement). After generation, the certificate is distributed manually or using automated 

protocols to the RA, the public-key owner, or a certificate repository (i.e., a directory) in 

accordance with the CA’s certification practice statement. 

8.1.5.1.1.3 General Distribution

Public keys may be distributed to entities other than an RA or CA in several ways. Distribution 

methods include:

1. Manual distribution of the public key itself by the owner of the public key (e.g., in a 

face-to-face transfer or by a bonded courier); the mandatory assurances listed in Section 

8.1.5.1.1 shall be provided to the recipient prior to the use of the public key 

operationally. 

2. Manual (e.g., in a face-to-face transfer or by receipted mail) or automated distribution 

of a public-key certificate by the public-key owner, the CA, or a certificate repository 

(i.e., a directory). The mandatory assurances listed in Section 8.1.5.1.1 that are not 

provided by the CA (e.g., public-key validation) shall be provided to or performed by 

the receiver of the public key prior to the use of the key operationally.

3. Automated distribution of a public key (e.g., using a communication protocol with 

authentication and content integrity). The mandatory assurances listed in Section 

8.1.5.1.1 shall be provided to the receiving entity prior to the use of the public key 

operationally.

8.1.5.1.2 Distribution of Ephemeral Public Keys

When used, ephemeral public keys are distributed as part of a secure key-agreement protocol. 

The key-agreement process (i.e., the key-agreement scheme + the protocol + key confirmation 

+ any associated negotiation + local processing) should provide a recipient with the assurances 

listed in Section 8.1.5.1.1. The recipient of an ephemeral public key shall obtain assurance of 

validity of that key as specified in [SP800-56A] prior to using that key for subsequent steps in 

the key-agreement process. 

8.1.5.1.3 Distribution of Centrally Generated Key Pairs

When a static key pair is centrally generated, the key pair shall be generated within a FIPS

140-validated cryptographic module or obtained from another source approved by the U.S. 

government for protecting national security information for subsequent delivery to the intended 

owner of the key pair. A signing key pair generated by a central key-generation facility for its 

subscribers will not provide strong support for non-repudiation for those individual 

subscribers; therefore, when support for non-repudiation is required by those subscribers, the 

subscribers should generate their own signing key pairs. However, if the central keygeneration facility generates signing key pairs for its own organization and distributes them to 

members of the organization, then support for non-repudiation may be provided at an 

organizational level (but not an individual level).

The private key of a key pair generated at a central facility shall only be distributed to the 

intended owner of the key pair. The confidentiality of the centrally generated private key shall 
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be protected, and the procedures for distribution shall include an authentication of the 

recipient's identity as established during user registration (see Section 8.1.1).

The key pair may be distributed to the intended owner using an appropriate manual method 

(e.g., courier, mail or other method specified by the key-generation facility) or secure 

automated method (e.g., a secure communication protocol). The private key shall be 

distributed in the same manner as a symmetric key (see Section 8.1.5.2.2). During the 

distribution process, each key of the key pair shall be provided with the appropriate protections 

for that key (see Section 6.1). 

When split-knowledge procedures are used for the manual distribution of the private key, the 

key shall be split into multiple key components that have the same security properties as the 

original key (e.g., randomness); each key component shall provide no knowledge of the value 

of the original key (e.g., each key component shall appear to be generated randomly).

Upon receipt of the key pair, the owner shall obtain assurance of the validity of the public key 

(see [SP800-56A], [SP800-56B] and [SP800-89]). The owner shall obtain assurance that the 

public and private keys of the key pair are correctly associated (i.e., check that they are a 

consistent pair, for example, by checking that a key encrypted under a public key-transport key 

can be decrypted by the corresponding private key-transport key). 

8.1.5.2 Generation and Distribution of Symmetric Keys 

The symmetric keys used for the encryption and decryption of data or other keys and for the 

computation of MACs (see Sections 4.2.2 and 4.2.3) shall be determined by an approved

method and shall be provided with protection that is consistent with Section 6.

Symmetric keys shall be either:

1. Generated and subsequently distributed (see Sections 8.1.5.2.1 and 8.1.5.2.2) either 

manually (see Section 8.1.5.2.2.1), using a public key-transport mechanism (see

Section 8.1.5.2.2.2), or using a previously distributed or agreed-upon key wrapping key 

(see Section 8.1.5.2.2.2), 

2. Established using a key-agreement scheme (i.e., the generation and distribution are 

accomplished with one process) (see Section 8.1.5.2.3), or

3. Derived from a master key (see Section 8.2.4).

8.1.5.2.1 Key Generation

Symmetric keys determined by key generation methods shall be either generated by an 

approved method (e.g., using an approved random number generator), or derived from a 

master key (see Section 8.2.4) using an approved key-derivation function (see [SP800-108]).

Also, see [SP800-133].

When split-knowledge procedures are used, the key shall exist outside of a [FIPS140]

cryptographic module as multiple key components. The keying material may be created within 

a cryptographic module and then split into components for export from the module, or may be 

created as separate components. Each key component shall provide no knowledge of the key 

value (e.g., each key component must appear to be generated randomly). If knowledge of k 

components is required to construct the original key, then knowledge of any k-1 key 

components shall provide no information about the original key other than, possibly, its length. 
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Note: A suitable combination function is not provided by simple concatenation; e.g., it is not 

acceptable to form a 128-bit key by concatenating two 64-bit key components.

All keys and key components shall be generated within a FIPS 140-validated cryptographic 

module or obtained from another source approved by the U.S. Government for the protection 

of national security information. 

8.1.5.2.2 Key Distribution

Keys generated in accordance with Section 8.1.5.2.1 as key-wrapping keys (i.e., keyencrypting keys), as master keys to be used for key derivation, or for the protection of 

communicated information are distributed manually (manual key transport) or using an 

automated key-transport protocol (automated key transport).

Keys used only for the storage of information (i.e., data or keying material) shall not be 

distributed except for backup or to other authorized entities that may require access to the 

stored information protected by the keys.

8.1.5.2.2.1 Manual Key Distribution 

Keys distributed manually (i.e., by other than an automated key-transport protocol) shall be 

protected throughout the distribution process. During manual distribution, secret or private 

keys shall either be wrapped (i.e., encrypted) or be distributed using appropriate physical 

security procedures. If multi-party control is desired, split-knowledge procedures may be used 

as well. The manual distribution process shall assure that:

1. The distribution of the keys is from an authorized source,

2. Any entity distributing plaintext keys is trusted by both the entity that generates the 

keys and the entity(ies) that receives the keys,

3. The keys are protected in accordance with Section 6, and

4. The keys are received by the authorized recipient. 

When distributed in encrypted form, the key shall be encrypted by an approved key-wrapping

scheme using a key-wrapping key that is used only for key wrapping, or by an approved keytransport scheme using a public key-transport key owned by the intended recipient. The keywrapping key or public key-transport key shall have been distributed as specified in this 

Recommendation.

When using split-knowledge procedures, each key component shall be either encrypted or 

distributed separately to each individual. Appropriate physical security procedures shall be 

used to protect each key component as sensitive information.

Physical security procedures may be used for all forms of manual key distribution. However, 

these procedures are particularly critical when the keys are distributed in plaintext form. In 

addition to the assurances listed above, accountability and auditing of the distribution process 

(see Sections 9.1 and 9.2) should be used.

8.1.5.2.2.2 Automated Key Distribution/Key Transport/Key Wrapping

Automated key distribution, also known as key transport or key wrapping, is used to distribute 

keys via a communication channel (e.g., the Internet or a satellite transmission). This requires 
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the prior distribution of a key-wrapping key (i.e., a key-encryption key) or a public keytransport key as follows:

1. A key-wrapping key shall be generated and distributed in accordance with Sections 

8.1.5.2.1 and 8.1.5.2.2, or established using a key-agreement scheme as defined in 

Section 8.1.5.2.3.

2. A public key-transport key shall be generated and distributed as specified in Section 

8.1.5.1. 

Only approved key-wrapping or public key-transport schemes shall be used. The approved

schemes provide assurance that:

a. For symmetric key-wrapping schemes: The key-wrapping key and the distributed key 

are not disclosed or modified. Approved key-wrapping methods that provide both 

confidentiality and integrity protection are provided in [SP800-38F]. 

b. For asymmetric key-transport schemes: The private key-transport key and the 

distributed key are not disclosed or modified, and correct association between the 

private and public key-transport keys is maintained. Approved key-transport schemes 

using asymmetric techniques are provided in [SP800-56A] and [SP800-56B].

c. The keys are protected in accordance with Section 6.

In addition, the approved schemes, together with the associated key-establishment protocol, 

should provide the following assurances:

d. Each entity in the key-distribution process knows the identifier associated with the 

other entity(ies),

e. The keys are correctly associated with the entities involved in the key-distribution 

process, and

f. The keys have been received correctly.

8.1.5.2.3 Key Agreement

Key agreement is used in a communication environment to establish keying material using 

information contributed by all entities in the communication (most commonly, only two 

entities) without actually sending the keying material. Only approved key-agreement schemes 

shall be used. Approved key-agreement schemes using asymmetric techniques are provided in 

[SP800-56A] and [SP800-56B]. Key agreement uses asymmetric key pairs to calculate shared 

secrets, which are then used to derive symmetric keys and other keying material (e.g., IVs). 

A key-agreement scheme uses either static or ephemeral asymmetric key pairs or both. The 

asymmetric key pairs should be generated and distributed as discussed in Section 8.1.5.1. 

Keying material derived from a key-agreement scheme shall be protected as specified in 

Section 6. 

A key-agreement scheme and its associated key-establishment protocol should provide the 

following assurances: 

1. The identifiers for entities involved in the key-establishment protocol are correctly 

associated with those entities. Assurance for the association of identifiers to entities 

may be achieved by the key-agreement scheme or may be achieved by the protocol in 
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which key agreement is performed. Note that the identifier may be a “pseudoidentifier,” not the identifier appearing on the entity’s birth certificate, for example.

In the general case, an identifier is associated with each party involved in the keyestablishment protocol, and each entity in the key-establishment process must be able 

to associate all the other entities with their appropriate identifier. In special cases, such 

as the secure distribution of public information on a web site, the association with an 

identifier may only be required for a subset of the entities (e.g., only the server).

2. The keys used in the key-agreement scheme are correctly associated with the entities 

involved in the key-establishment process.

3. The derived keys are correct.

Keys derived through key agreement and its enabling protocol should not be used to protect 

and send information until the three assurances described above have been achieved.

8.1.5.3 Generation and Distribution of Other Keying Material

Keys are often generated in conjunction with or are used with other keying material. This other 

keying material shall be protected in accordance with Section 6.2. Table 6 specifies the type(s) 

of protection required for keying material other than keys.

8.1.5.3.1 Domain Parameters

Domain parameters are used by some public-key algorithms to generate key pairs, to compute 

digital signatures, or to establish keys. Typically, domain parameters are generated 

infrequently and used by a community of users for a substantial period of time. Domain 

parameters may be distributed in the same manner as the public keys with which they are 

associated, or they may be made available at some other accessible site. Assurance of the 

validity of the domain parameters shall be obtained prior to use, either by a trusted entity that 

vouches for the parameters (e.g., a CA), or by the entities themselves. Assurance of domainparameter validity is addressed in [SP800-89] and [SP800-56A]. Obtaining this assurance 

should be addressed in a CA’s certification practices statement or an organization's security 

plan.

8.1.5.3.2 Initialization Vectors

Initialization vectors (IVs) are used by symmetric-key algorithms in several modes of 

operation for encryption and decryption, for authentication, or both. The criteria for the 

generation and use of IVs are provided in the [SP800-38] series of publications; IVs shall be 

protected as specified in Section 6. When distributed, IVs may be distributed in the same 

manner as their associated keys, or may be distributed with the information that uses the IVs as 

part of the cryptographic mechanism.

8.1.5.3.3 Shared Secrets

Shared secrets are computed during an asymmetric key-agreement scheme and are 

subsequently used to derive keying material. Shared secrets are generated as specified by an 

appropriate key-agreement scheme (see [SP800-56A] and [SP800-56B]), and shall not be used 

directly as keying material. 
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8.1.5.3.4 RBG Seeds

A Random Bit Generator (RBG) is a device or algorithm that outputs a sequence of bits that is 

unpredictable; RBGs are often called Random Number Generators. Approved RBGs are 

specified in [SP800-90]. RBGs depend on the introduction of truly random bits called seeds, 

which are used to initialize an RBG and that must be kept secret. An initialized RBG is often 

used to generate keys and other values requiring unpredictability. The seeds themselves shall 

not be used for any purpose other than RBG input. Seeds shall only be transmitted using 

secure channels that protect the confidentiality and integrity of the seeds, as well as providing 

replay protection41 and mutual authentication42. 

8.1.5.3.5 Other Public and Secret Information

Public and secret information may be used during the seeding of an RBG (see Section 

8.1.5.3.4) or during the generation or establishment of keying material (see [SP800-56A], 

[SP800-56B] and [SP800-108]). Public information may be distributed; secret information 

shall be protected in the same manner as a private or secret key during distribution.

8.1.5.3.6 Intermediate Results

Intermediate results occur during computation using cryptographic algorithms. These results 

shall not be distributed as or with the keying material. 

8.1.5.3.7 Random Bits/Numbers

Random bits (or numbers) are used for many purposes, including the generation of keys and 

nonces, and the issuing of challenges during communication protocols. Random bits may be 

distributed, but whether or not confidentiality protection is required depends on the context in 

which the random bits are used.

8.1.5.3.8 Passwords

Passwords are used for identity authentication or authorization, and, in some cases, to derive 

keying material (see [SP800-132]). Passwords may be distributed, but their protection during 

distribution shall be consistent with the protection required for their use. For example, if the 

password will be used to access cryptographic keys that are used to provide 128 bits of security 

strength when protecting data, then the password needs to be provided with at least 128 bits of 

protection as well. Note that poorly selected passwords may not themselves provide the 

required amount of protection for key access and are potentially the weak point of the process; 

i.e., it may be far easier to guess the password than to attempt to “break” the cryptographic 

protection used on the password. It is the responsibility of users and organizations to select 

passwords that provide the requisite amount of protection for the keys they protect.

8.1.6 Key Registration Function

Key registration results in the binding of keying material to information associated with a 

particular entity. Keys that would be registered include the public key of an asymmetric key 

pair and the symmetric key used to bootstrap an entity into a system. Normally, keys generated 

during communications (e.g., using key-agreement schemes or key derivation functions) would 

 41 Assurance that a valid data transmission is not maliciously or fraudulently repeated or delayed.

42 Authentication by each party in a transaction of the identity of the other party.
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not be registered. Information provided during registration typically includes the identifier of 

the entity associated with the keying material and the intended use of the keying material (e.g., 

as a signing key, data-encryption key, etc.). Additional information may include authorization 

information or specify a level of trust. The binding is performed after the entity’s identity has 

been authenticated by a means that is consistent with the system policy (see Section 8.1.1). The 

binding provides assurance to the community-at-large that the keying material is used by the 

correct entity in the correct application. The binding is often cryptographic, which creates a 

strong association between the keying material and the entity. A trusted third party performs 

the binding. Examples of a trusted third party include a Kerberos realm server or a PKI 

certification authority (CA). Identifiers issued by a trusted third party shall be unique to that 

party.

When a Kerberos realm server performs the binding, a symmetric key is stored on the server 

with the corresponding metadata. In this case, the registered keying material is maintained in 

secure storage (i.e., the keys are provided with confidentiality and integrity protection).

When a CA performs the binding, the public key and associated information (often called 

attributes) are placed in a public-key certificate, which is digitally signed by the CA. In this 

case, the registered keying material may be made publicly available.

When a CA provides a certificate for a public key, the public key shall be verified to ensure 

that it is associated with the private key known by the purported owner of the public key. This 

provides assurance of possession. When POP is used to obtain assurance of possession, the 

assurance shall be accomplished as specified in Section 8.1.5.1.1.2. 

8.2 Operational Phase

Keying material used during the cryptoperiod of a key is often stored for easy access as 

needed. During storage, the keying material shall be protected as specified in Section 6.2.2. 

During normal use, the keying material is stored either on the device or module that uses that 

material, or on an immediately accessible storage media. When the keying material is required 

for operational use, the keying material is acquired from immediately accessible storage when 

not present in active memory within the device or module.

To provide continuity of operations when the keying material becomes unavailable for use 

from normal operational storage during its cryptoperiod (e.g., because the material is lost or 

corrupted), keying material may need to be recoverable. If an analysis of system operations 

indicates that the keying material needs to be recoverable, then the keying material shall either

be backed up (see Section 8.2.2.1), or the system shall be designed to allow reconstruction 

(e.g., re-derivation) of the keying material. Retrieving or reconstructing keying material from 

backup or an archive is commonly known as key recovery (see Section 8.2.2.2).

At the end of a key’s cryptoperiod, a new key needs to be available to replace the old key if 

operations are to be continued. This can be accomplished by re-keying (see Section 8.2.3.1) or 

by key derivation (see Section 8.2.4). A key shall be destroyed in accordance with Section

8.3.4 and should be destroyed as soon as that key is no longer needed in order to reduce the 

risk of exposure.
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8.2.1 Normal Operational Storage Function

One objective of key management is to facilitate the operational availability of keying material 

for standard cryptographic purposes. Usually, a key remains operational until the end of the 

key’s cryptoperiod (i.e., the expiration date). During normal operational use, keying material is 

available either in the device or module (e.g., in RAM) or in an immediately accessible storage 

media (e.g., on a local hard disk). 

8.2.1.1 Cryptographic Module Storage

Keying material may be stored in the cryptographic module that adds, checks, or removes the 

cryptographic protection on information. The storage of the keying material shall be consistent 

with Section 6.2.2, as well as with [FIPS140].

8.2.1.2 Immediately Accessible Storage Media

Keying material may need to be stored for normal cryptographic operations on an immediately

accessible storage media (e.g., a local hard drive) during the cryptoperiod of the key. The 

storage requirements of Section 6.2.2 shall apply to this keying material. 

8.2.2 Continuity of Operations Function

Keying material can become lost or unusable, due to hardware damage, corruption or loss of 

program or data files, system policy, or configuration changes. In order to maintain the 

continuity of operations, it is often necessary for users and/or administrators to be able to 

recover keying materials from backup storage. However, if operations can be continued 

without the backup of keying material (e.g., by re-keying), or the keying material can be 

recovered or reconstructed without being saved, it may be preferable not to save the keying 

material in order to lessen the possibility of a compromise of the keying material or other 

cryptographically related information.

The compromise of keying material affects the continuity of operations (see Section 8.4). 

When keying material is compromised, the continuity of operations requires the establishment 

of entirely new keying material (see Section 8.1.5), following an assessment of what keying 

material is affected and needs to be replaced.

8.2.2.1 Backup Storage

The backup of keying material on an independent, secure storage media provides a source for 

key recovery (see Section 8.2.2.2). Backup storage is used to store copies of information that 

are also currently available in normal operational storage during a key’s cryptoperiod (i.e., in 

the cryptographic module, or on an immediately accessible storage media - see Section 

8.2.1.1). Not all keys need to be backed up. The storage requirements of Section 6.2.2 apply to 

keying material that is backed up. Tables 7 and 8 provide guidance about the backup of each 

type of keying material and other related information. An “OK” indicates that storage is 

permissible, but not necessarily required. The final determination for backup should be made 

based on the application in which the keying material is used. A detailed discussion about the 

backup of each type of key and other cryptographic information is provided in Appendix B.3.

Keying material maintained in backup should remain in storage for at least as long as the same

keying material is maintained in storage for normal operational use (see Section 8.2.1). When 

no longer needed for normal operational use, the keying material and other related information 
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should be removed from backup storage. When removed from backup storage, all traces of the 

information in backup storage shall be destroyed in accordance with Section 8.3.4.

A discussion of backup and recovery is provided in [ITLBulletin].

Table 7: Backup of keys

Type of Key Backup?

Private signature key No (in general); support for non-repudiation would be in 

question. However, backup may be warranted in some 

cases − a CA’s private signing key, for example. When 

required, any backed up keys shall be stored under the 

owner’s control.

Public signature-verification key OK; its presence in a public-key certificate that is 

available elsewhere may be sufficient.

Symmetric authentication key OK

Private authentication key OK, if required by an application.

Public authentication key OK; if required by an application.

Symmetric data encryption key OK

Symmetric key-wrapping key OK

Random number generation key Not necessary and may not be desirable, depending on 

the application.

Symmetric master key OK

Private key-transport key OK

Public key-transport key OK; its presence in a public-key certificate that is 

available elsewhere may be sufficient.

Symmetric key-agreement key OK

Private static key-agreement key OK

Public static key-agreement key OK; its presence in a public-key certificate that is 

available elsewhere may be sufficient.

Private ephemeral key-agreement

key

No

Public ephemeral key-agreement key OK 

Symmetric authorization key OK

Private authorization key OK

Public authorization key OK; its presence in a public-key certificate that is 

available elsewhere may be sufficient.
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Table 8: Backup of other cryptographic or related information

Type of Keying Material Backup?

Domain parameters OK

Initialization vector OK, if necessary

Shared secret No

RBG seed No

Other public information OK

Other secret information OK

Intermediate results No

Key control information (e.g., IDs, 

purpose, etc.)

OK

Random number Depends on the application or use of the random number.

Passwords OK when used to derive keys or to detect the reuse of 

passwords; otherwise, No

Audit information OK

8.2.2.2 Key Recovery Function

Keying material that is in active memory or stored in normal operational storage may 

sometimes be lost or corrupted (e.g., from a system crash or power fluctuation). Some of the 

keying material is needed to continue operations and cannot easily be replaced. An assessment 

needs to be made of which keying material needs to be preserved for possible recovery at a 

later time.

The decision as to whether key recovery is required should be made on a case-by-case basis. 

The decision should be based on:

1. The type of key (e.g., private signature key or symmetric data-encryption key);

2. The application in which the key will be used (e.g., interactive communications or file 

storage);

3. Whether the key is “owned” by the local entity (e.g., a private key) or by another entity 

(e.g., the other entity's public key) or is shared (e.g., a symmetric data-encryption key 

shared by two entities);

4. The role of the entity in a communication (e.g., sender or receiver); and

5. The algorithm or computation in which the key will be used (e.g., does the entity have 

the necessary information to perform a given computation if the key were to be 

recovered)43.

 43 This could be the case when performing a key-establishment process for some key-establishment schemes (see 

[SP800-56A] and [SP800-56B]).
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The factors involved in a decision for or against key recovery should be carefully assessed. 

The trade-offs are concerned with continuity of operations versus the risk of possibly exposing 

the keying material and the information it protects if control of the keying material is lost. If it 

is determined that a key needs to be recovered, and the key is still active (e.g., the cryptoperiod 

of the key has not expired, and the key has not been compromised), then the key may be 

replaced in order to limit the exposure of the data protected by that key (see Section 8.2.3).

Issues associated with key recovery and discussions about whether or not different types of 

cryptographic material need to be recoverable are provided in Appendix B.

8.2.3 Key Change Function

Key change is the replacement of a key with another key that performs the same function as 

the original key. There are several reasons for changing a key.

1. The key may have been compromised,

2. The key’s cryptoperiod may be nearing expiration, or

3. It may be desirable to limit the amount of data protected with any given key.

8.2.3.1 Re-keying 

If the new key is generated in a manner that is entirely independent of the “value” of the old 

key, the process is known as re-keying. This replacement shall be accomplished using one of 

the key-establishment methods discussed in Section 8.1.5. Re-keying is used when a key has 

been compromised (provided that the re-keying scheme itself is not compromised) or when the 

cryptoperiod is nearing expiration. 

8.2.3.2 Key Update Function

If the “value” of the new key is dependent on the value of the old key, the process is known as 

key update (i.e., the current key is modified to create a new key). Key update is a special case 

of key derivation (see Section 8.2.4), where the derived key replaces the key used to derive it. 

For example, suppose that K1 is used as an encryption key. When K1 needs to be replaced, it is 

used to derive K2. K2 is then used as the new encryption key until it is replaced by K3, which is 

derived from K2.

Key update could result in a security exposure if an adversary obtains a key in the chain of 

keys and knows the update process used; keys subsequent to the compromised key could easily 

be determined.

Federal applications shall not use key update (also, see [SP800-152]).

8.2.4 Key Derivation Methods

Cryptographic keys may be derived from a secret value. The secret value, together with other 

information, is input into a key-derivation method (e.g., a key-derivation function) that outputs 

the required key(s). In contrast to key change (as discussed in Section 8.2.3), the derived keys 

are often used for new purposes, rather than for replacing the secret values from which they are 

derived. The derivation method shall be non-reversible (i.e., a one-way function) so that the 

secret value cannot be determined from the derived keys. In addition, it shall not be possible to 

determine a derived key from other derived keys. It should be noted that the strength of a 
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derived key is no greater than the strength of the derivation algorithm and the secret value from 

which the key is derived. 

Three commonly used key-derivation cases are discussed below.

1. Two parties derive common keys from a common shared secret. This approach is used 

in the key-establishment techniques specified in [SP800-56A] and [SP800-56B]. The 

security of this process is dependent on the security of the shared secret and the specific 

key-derivation method used. If the shared secret is known, the derived keys may be 

determined. A key-derivation method specified or allowed in [SP800-56A], [SP800-

56B] or [SP800-56C] shall be used for this purpose. These derived keys may be used to 

provide the same confidentiality, identity authentication, and source authentication 

services as randomly generated keys, with a security strength determined by the scheme 

and key pairs used to generate the shared secret.

2. Keys derived from a key-derivation key (master key). This is often accomplished by 

using the key-derivation key, entity ID, and other known information as input to a 

function that generates the keys. One of the key-derivation functions defined in 

[SP800-108] shall be used for this purpose. The security of this process depends upon 

the security of the key-derivation key and the key-derivation function. If the keyderivation key is known by an adversary, he can generate any of the derived keys. 

Therefore, keys derived from a key-derivation key are only as secure as the keyderivation key itself. As long as the key-derivation key is kept secret, the derived keys 

may be used in the same manner as randomly generated keys.

3. Keys derived from a password. A user-generated password, by its very nature, is less

random (i.e., has lower entropy) than is required for a cryptographic key; that is, the 

number of passwords that are likely to be used to derive a key is significantly smaller 

than the number of keys that are possible for a given key size. In order to increase the 

difficulty of exhaustively searching the likely passwords, a key-derivation function is 

iterated a large number of times. The key is derived using a password, entity ID, and 

other known information as input to the key-derivation function. The security of the 

derived key depends upon the security of the password and the key-derivation process. 

If the password is known or can be guessed, then the corresponding derived key can be 

generated. Therefore, keys derived in this manner are likely to be less secure than 

randomly generated keys or keys derived from a shared secret or key-derivation key. 

For storage applications, one of the key-derivation methods specified in [SP800-132]

shall be used to derive keys. For non-storage applications, keys derived in this manner 

shall be used for integrity, and source authentication purposes only and not for general 

encryption. 

8.3 Post-Operational Phase

During the post-operational phase, keying material is no longer in operational use, but access 

to the keying material may still be possible.

8.3.1 Archive Storage and Key Recovery Functions

A key archive is a repository containing keying material and other related information for 

recovery beyond the cryptoperiod of the keys. Not all keying material needs to be archived. An 
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organization’s security plan should indicate the types of information that are to be archived 

(see [SP800-57, Part 2]).

The archive shall continue to provide the appropriate protections for each key and any other 

related information in the archive, as specified in Section 6.2.2. The archive will require a 

strong access-control mechanism to limit access to only authorized entities. When keying 

material is entered into the archive, it is often time-stamped so that the date-of-entry can be 

determined. This date may itself be cryptographically protected so that it cannot be changed 

without detection. 

If keying material needs to be recoverable (e.g., after the end of its cryptoperiod), either the 

keying material shall be archived, or the system shall be designed to allow reconstruction (e.g., 

re-derivation) of the keying material from archived information. Retrieving the keying material 

from archive storage or by reconstruction is commonly known as key recovery. The archive 

shall be maintained by a trusted party (e.g., the organization associated with the keying 

material or a trusted third party).

While in storage, archived information may be either static (i.e., never changing) or may need 

to be re-encrypted under a new archive-encryption key from time-to-time. Archived data 

should be stored separately from operational data, and multiple copies of archived 

cryptographic information should be provided in physically separate locations (i.e., it is 

recommended that the key archive be backed up). For critical information that is encrypted 

under archived keys, it may be necessary to back up the archived keys and to store multiple 

copies of these archived keys in separate locations.

When archived, keying material should be archived prior to the end of the cryptoperiod of the 

key. For example, it may be prudent to archive the keying material during key activation. 

When no longer required, the keying material shall be destroyed in accordance with Section 

8.3.4. 

The confidentiality of archived information is provided by an archive-encryption key (one or 

more encryption keys that are used exclusively for the encryption of archived information), by 

another key that has been archived, or by a key that may be derived from an archived key. 

Note that the algorithm with which the archive-encryption key is used may also provide 

integrity protection for the encrypted information. When encrypted by the archive-encryption 

key, the encrypted keying material shall be re-encrypted by any new archive-encryption key at 

the end of the cryptoperiod of the old archive-encryption key. When the keying material is reencrypted, integrity values on that keying material shall be recomputed. This may impose a 

significant burden; therefore, the strength of the cryptographic algorithm and archiveencryption key shall be selected to minimize the need for re-encryption. 

When the archive-encryption key and its associated algorithm do not also provide integrity 

protection for the encrypted information, integrity protection shall be provided by a separate 

archive-integrity key (i.e., one or more authentication or digital-signature keys that are used 

exclusively for the archive) or by another key that has been archived. If integrity protection is 

to be maintained at the end of the cryptoperiod of the archive-integrity key, new integrity 

values shall be computed on the archived information on which the old archive-integrity key 

was applied.
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When the confidentiality and integrity protection of the archived information is provided using 

separate processes, the archive-encryption key and archive-integrity key (when used) shall be 

different from each other (e.g., independently generated), and shall be protected in the same 

manner as their key type (see Section 6). Note that these two services can also be provided 

using authenticated encryption, which uses a single cryptographic algorithm operation and a 

single key.

Tables 9 and 10 indicate the appropriateness of archiving keys and other cryptographically

related information. An “OK” in column 2 (Archive?) indicates that archival is permissible, 

but not necessarily required. Column 3 (Retention period) indicates the minimum time that the 

key should be retained in the archive. Additional advice on the storage of keying material in 

archive storage is provided in Appendix B.3.

Table 9: Archive of keys

Type of Key Archive? Retention period (minimum)

Private signature key No

Public signature-verification

key

OK Until no longer required to verify data 

signed with the associated private key

Symmetric authentication key OK Until no longer needed to authenticate data

or an identity.

Private authentication key No

Public authentication key OK

Symmetric data-encryption 

key

OK Until no longer needed to decrypt data 

encrypted by this key

Symmetric key-wrapping key OK Until no longer needed to decrypt keys 

encrypted by this key

Symmetric random number 

generator key

No

Symmetric master key OK, if needed 

to derive other 

keys for 

archived data

Until no longer needed to derive other keys

Private key-transport key OK Until no longer needed to decrypt keys 

encrypted by this key

Public key-transport key OK

Symmetric key-agreement key OK

Private static key-agreement

key

OK

Public static key-agreement

key

OK Until no longer needed to reconstruct 

keying material.
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Type of Key Archive? Retention period (minimum)

Private ephemeral keyagreement keyNo

Public ephemeral keyagreement keyOK

Symmetric authorization key No

Private authorization key No

Public authorization key OK

Table 10: Archive of other cryptographic related information

Type of Key Archive? Retention period (minimum)

Domain parameters OK Until all keying material, signatures and 

signed data using the domain parameters are 

removed from archives

Initialization vector OK; normally 

stored with the 

protected 

information

Until no longer needed to process the 

protected data

Shared secret No 

RBG seed No 

Other public information OK Until no longer needed to process data using 

the public information

Other secret information OK Until no longer needed to process data using 

the secret information

Intermediate result No

Key control information (e.g., 

IDs, purpose)

OK Until the associated key is removed from 

the archive

Random number Depends on the application or use of the 

random number

Password OK when used 

to derive keys 

or to detect the 

reuse of 

passwords; 

otherwise, No 

Until no longer needed to (re-)derive keys 

or to detect password reuse

Audit information OK Until no longer needed
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The recovery of archived keying material may be required to remove (e.g., decrypt) or check 

(e.g., verify a digital signature or a MAC) the cryptographic protections on other archived data; 

recovered keys shall not be used to apply cryptographic protection. The key recovery process 

results in retrieving or reconstructing the desired keying material from archive storage in order 

to perform the required cryptographic operation. Immediately after completing this operation, 

the keying material shall be erased from the cryptographic process44 for which it was 

recovered (i.e., it shall not be used for normal operational activities). However, the key shall

be retained in the archive (see Section 8.3.4) as long as needed. Further advice on key recovery 

issues is provided in Appendix B.

8.3.2 Entity De-registration Function

The entity de-registration function removes the authorizations of an entity to participate in a 

security domain. When an entity ceases to be a member of a security domain, the entity shall

be de-registered. De-registration is intended to prevent other entities from relying on or using 

the de-registered entity's keying material. 

All records of the entity and the entity’s associations shall be marked to indicate that the entity 

is no longer a member of the security domain, but the records should not be deleted. To reduce 

confusion and unavoidable human errors, identification information associated with the deregistered entity should not be re-used (at least for a period of time). For example, if a “John 

Wilson” retires and is de-registered on Friday, the identification information assigned to his 

son “John Wilson”, who is hired the following Monday, should be different.

8.3.3 Key De-registration Function

Registered keying material may be associated with the identity of a key owner, owner 

information (e.g., email address), role, or authorization information. When the keying material 

is no longer needed, or the associated information becomes invalid, the keying material should

be de-registered (i.e., all records of the keying material and its associations should be marked 

to indicate that the key is no longer in use) by the appropriate trusted third party. In general, 

this will be the trusted third party that registered the key (see Section 8.1.6).

Keying material should be de-registered when the information associated with an entity is 

modified. For example, if an entity's email address is associated with a public key, and the 

entity's address changes, the keying material should be de-registered to indicate that the 

associated information has become invalid. Unlike the case of a key compromise, the entity 

could safely re-register the public key after modifying the entity's information through the user 

registration process (see Section 8.1.1).

When a registered cryptographic key is compromised, that key and any associated keying 

material shall be de-registered. When the compromised key is the private part of a publicprivate key pair, the public key shall also be revoked (see Section 8.3.5). If the registration 

information associated with a public-private key pair is changed, but the private key has not 

been compromised, the public key should be revoked with an appropriate reason code (see 

Section 8.3.5).

 44 For example, an archived symmetric key could be recovered to decrypt a single message or file, or could be 

used to decrypt multiple messages or files, all of which were encrypted using that key during its originator-usage 

period.
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8.3.4 Key Destruction Function

When copies of cryptographic keys are made, care should be taken to provide for their eventual 

destruction. All copies of the private or symmetric key shall be destroyed as soon as they are 

no longer required (e.g., for archival or reconstruction activity) in order to minimize the risk of 

a compromise. Keys shall be destroyed in a manner that removes all traces of the keying 

material so that it cannot be recovered by either physical or electronic means45. Public keys 

may be retained or destroyed, as desired.

8.3.5 Key Revocation Function

It is sometimes necessary to remove keying material from use prior to the end of its normal 

cryptoperiod for reasons that include key compromise, removal of an entity from an 

organization, etc. This process is known as key revocation and is used to explicitly revoke a 

symmetric key or the public key of a key pair, although the private key corresponding to the 

public key is also revoked. 

Key revocation may be accomplished using a notification indicating that the continued use of 

the keying material is no longer recommended. The notification could be provided by actively 

sending the notification to all entities that might be using the revoked keying material, or by 

allowing the entities to request the status of the keying material (i.e., a “push” or a “pull” of the 

status information). The notification should include a complete identification of the keying 

material (excluding the key itself), the date and time of revocation and the reason for 

revocation, when appropriate (e.g., a key compromise). Based on the revocation information 

provided, other entities could then make a determination of how they will treat information 

protected by the revoked keying material. 

For example, if a public signature-verification key is revoked because an entity left an 

organization, it may be appropriate to honor all signatures created prior to the revocation date

(i.e., to continue to verify those signatures and accept them as valid if the verification is 

successful). If a signing private key is compromised, resulting in the revocation of the 

corresponding public key, an assessment needs to be made as to whether or not information 

signed prior to the revocation notice would be considered as valid. 

As another example, a symmetric key that is used to generate MACs may be revoked so that it 

will not be used to generate MACs on new information. However, the key may be retained so 

that archived documents can be verified.

The details for key revocation should reflect the lifecycle for each particular key. If a key is 

used in a pair-wise situation (e.g., two entities communicating using the same encryption key), 

the entity revoking the key shall inform the other entity of the revocation. If the key has been 

registered with an infrastructure, the entity revoking the key cannot always directly inform the 

other entities that may rely upon that key. Instead, the entity revoking the key shall inform the 

infrastructure that the key needs to be revoked (e.g., using a certificate revocation request). The 

infrastructure shall respond by de-registering the key material (see Section 8.3.3).

 45 A simple deletion of the keying material might not completely obliterate the information. For example, erasing 

the information might require overwriting that information multiple times with other non-related information, 

such as random bits, or all zero or one bits. Keys stored in memory for a long time can become “burned in.” This 

can be mitigated by splitting the key into components that are frequently updated (see [DiCrescenzo]).
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In a PKI, key revocation is commonly achieved by including the certificate in a list of revoked 

certificates (i.e., a CRL). If the PKI uses online status mechanisms (e.g., the Online Certificate 

Status Protocol [RFC 2560]), revocation is achieved by informing the appropriate certificate 

status server(s). For example, when a private key is compromised, the corresponding publickey certificate shall be revoked as soon as possible. Certificate revocation because of a key 

compromise indicates that the binding between the owner and the key is no longer to be 

trusted; relying parties should not accept the certificate without seriously considering the risks 

and consulting the organization's policy about this situation. Other revocation reasons indicate 

that, even though the original binding may still be valid and the key was not compromised, the 

use of the public key in the certificate should be terminated; again, the relying party should

consult his organization's policy on this issue.

In a symmetric-key system, key revocation could, in theory, be achieved by simply deleting the 

key from the server’s storage. Key revocation for symmetric keys is more commonly achieved 

by adding the key to a blacklist or compromised key list; this helps satisfy auditing and 

management requirements.

8.4 Destroyed Phase

The keying material is no longer available. All records of its existence may have been deleted, 

though this is not required. Some organizations may require the retention of certain key 

metadata elements for audit purposes. For example, if a copy of an ostensibly destroyed key is 

found in an uncontrolled environment or is later determined to have been compromised, 

records of the identifier of the key, its type, and its cryptoperiod may be helpful in determining 

what information was protected under the key and how best to recover from the compromise. 

In addition, by keeping a record of the metadata of both destroyed and compromised keys, one 

will be able to track which keys transitioned through a normal lifecycle and which ones were 

compromised at some time during their lifecycle. Thus, protected information that is linked to 

key names that went through the normal lifecycle may still be considered secure, provided that 

the security strength of the algorithm remains sufficient. However, any protected information 

that is linked to a key name that has been compromised may itself be compromised. 
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9 Accountability, Audit, and Survivability

Systems that process valuable information require controls in order to protect the information 

from unauthorized disclosure and modification. Cryptographic systems that contain keys and 

other cryptographic information are especially critical. Three useful control principles and their 

application to the protection of keying material are highlighted in this section.

9.1 Accountability

Accountability involves the identification of those entities that have access to, or control of, 

cryptographic keys throughout their lifecycles. Accountability can be an effective tool to help 

prevent key compromises and to reduce the impact of compromises when they are detected. 

Although it is preferred that no humans be able to view keys, as a minimum, the key 

management system should account for all individuals who are able to view plaintext 

cryptographic keys. In addition, more sophisticated key-management systems may account for 

all individuals authorized to access or control any cryptographic keys, whether in plaintext or 

ciphertext form. For example, a sophisticated accountability system might be able to determine 

each individual who had control of any given key over its entire lifespan. This would include

the person in charge of generating the key, the person who used the key to cryptographically 

protect data, anyone else known to have accessed the key, and the person who was responsible 

for destroying the key when it was no longer needed. Even though these individuals may never 

have actually seen the key in plaintext form, they are held accountable for the actions that they 

performed on or with the key.

Accountability provides three significant advantages:

1. It aids in the determination of when the compromise could have occurred and what 

individuals could have been involved, 

2. It tends to protect against compromise, because individuals with access to the key know 

that their access to the key is known, and

3. When recovering from a detected key compromise, it is very useful in to know where 

the key was used and what data or other keys were protected by the compromised key.

Certain principles have been found to be useful in enforcing the accountability of 

cryptographic keys. These principles might not be applicable to all systems or all types of keys. 

Some of the principles apply to long-term keys that are controlled by humans. The principles 

include:

a. Uniquely identifying keys;

b. Identifying the key user;

c. Identifying the dates and times of key use, along with the data that is protected, and

d. Identifying other keys that are protected by a symmetric or private key.

9.2 Audit

Two types of audit should be performed on key-management systems:
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1. The security plan and the procedures that are developed to support the plan should be 

periodically audited to ensure that they continue to support the Key Management Policy 

(see [SP800-57, Part 2]).

2. The protective mechanisms employed should be periodically reassessed with respect to 

the level of security that they provide and are expected to provide in the future, and that 

the mechanisms correctly and effectively support the appropriate policies. New 

technology developments and attacks should be taken into consideration.

On a more frequent basis, the actions of the humans that use, operate and maintain the system 

should be reviewed to verify that the humans continue to follow established security 

procedures. Strong cryptographic systems can be compromised by lax and inappropriate 

human actions. Highly unusual events should be noted and reviewed as possible indicators of 

attempted attacks on the system.

9.3 Key Management System Survivability

9.3.1 Backup Keys

[OMB11/01] notes that encryption is an important tool for protecting the confidentiality of 

disclosure-sensitive information that is entrusted to an agency’s care, but that the encryption of 

agency data also presents risks to the availability of information needed for mission 

performance. Agencies are reminded of the need to protect the continuity of their information 

technology operations and agency services when implementing encryption. The guidance 

specifically notes that, without access to the cryptographic keys that are needed to decrypt 

information, organizations risk the loss of their access to that information. Consequently, it is 

prudent to retain backed up or archived copies of the keys necessary to decrypt stored 

enciphered information, including master keys, key-wrapping keys, and the related keying 

material necessary to decrypt encrypted information until there is no longer any requirement 

for access to the underlying plaintext information (see Tables 7 and 8 in Section 8.2.2.1).

As the tables in Section 8.2.2.1 show, there are other operational keys in addition to those 

associated with decryption that organizations may need to backup (e.g., public signatureverification keys and authorization keys). Backed up or archived copies of keying material 

shall be stored in accordance with the provisions of Section 6 in order to protect the 

confidentiality of encrypted information and the integrity of source authentication, integrity

authentication, and authorization processes.

9.3.2 Key Recovery 

There are several issues associated with key recovery. An extensive discussion is provided in 

Appendix B. Key recovery issues to be addressed include:

1. Which keying material, if any, needs to be backed up or archived for later recovery?

2. Where will backed-up or archived keying material be stored?

3. When will archiving be done (e.g., during key activation or at the end of a key’s 

cryptoperiod)?

4. Who will be responsible for protecting the backed-up or archived keying material?

5. What procedures need to be in place for storing and recovering the keying material?
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6. Who can request a recovery of the keying material and under what conditions?

7. Who will be notified when a key recovery has taken place and under what conditions?

8. What audit or accounting functions need to be performed to ensure that the keying 

material is only provided to authorized entities?

9.3.3 System Redundancy/Contingency Planning

Cryptography is a useful tool for preventing unauthorized access to data and/or resources, but 

when the mechanism fails, it can prevent access by valid users to critical information and 

processes. Loss or corruption of the only copy of cryptographic keys can deny users access to 

information. For example, a locksmith can usually defeat a broken physical mechanism, but 

access to information encrypted by a strong algorithm may not be practical without the correct 

decryption key. The continuity of an organization’s operations can depend heavily on 

contingency planning for key-management systems that includes a redundancy of critical 

logical processes and elements, including key management and cryptographic keys.

9.3.3.1 General Principles

Planning for recovery from system failures is an essential management function. Interruptions 

of critical infrastructure services should be anticipated, and planning for maintaining the 

continuity of operations in support of an organization’s primary mission requirements should

be done. With respect to key management, the following situations are typical of those for 

which planning is necessary:

1. Lost key cards or tokens;

2. Forgotten passwords that control access to keys;

3. The failure of key input devices (e.g., readers);

4. The loss or corruption of the memory media on which keys and/or certificates are 

stored;

5. The compromise of keys;

6. The corruption of Certificate Revocation Lists (CRLs) or Compromised Key Lists 

(CKLs);

7. Hardware failure of key or certificate generation, registration, and/or distribution 

systems, subsystems, or components;

8. Power loss requiring re-initialization of key or certificate generation, registration, 

and/or distribution systems, subsystems, or components;

9. The corruption of the memory media necessary for key or certificate generation, 

registration, and/or distribution systems, subsystems, or components;

10. The corruption or loss of key or certificate distribution records and/or audit logs;

11. The loss or corruption of the association of keying material to the owners/users of the 

keying material; and

12. The unavailability of older software or hardware that is needed to access keying 

material or process protected information.
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While recovery discussions most commonly focus on the recovery of encrypted data and the 

restoration of encrypted communication capabilities, planning should also address 1) the 

restoration of access (without creating a temporary loss of access protections) where 

cryptography is used in access control mechanisms, 2) the restoration of critical processes 

(without creating a temporary loss of privilege restrictions) where cryptography is used in 

authorization mechanisms, and 3) the maintenance/restoration of integrity protection in digital 

signature and message authentication applications.

Contingency planning should include 1) providing a means and assigning responsibilities for 

rapidly recognizing and reporting critical failures; 2) the assignment of responsibilities and the 

placement of resources for bypassing or replacing failed systems, subsystems, and 

components; and 3) the establishment of detailed bypass and/or recovery procedures. 

Contingency planning includes a full range of integrated logistics support functions. Spare 

parts (including copies of critical software programs, manuals, and data files) should be 

available (acquired or arranged for) and pre-positioned (or delivery-staged). Emergency 

maintenance, replacement, and/or bypass instructions should be prepared and disseminated to 

both designated individuals and to an accessible and advertised access point. Designated 

individuals should be trained in their assigned recovery procedures, and all personnel should

be trained in reporting procedures and workstation-specific recovery procedures. 

9.3.3.2 Cryptography and Key Management-specific Recovery Issues

Cryptographic keys are relatively small components or data elements that often control access 

to large volumes of information or critical processes. As the Office of Management and Budget 

has noted in [OMB11/01], “without access to the cryptographic key(s) needed to decrypt 

information, [an] agency risks losing access to its valuable information.” Agencies are 

reminded of the need to protect the continuity of their information technology operations and 

agency services when implementing encryption. The guidance particularly stresses that 

agencies must address information availability and assurance requirements through appropriate 

data recovery mechanisms, such as cryptographic key recovery.

A key recovery capability generally involves some redundancy, or multiple copies of keying 

material. If one copy of a critical key is lost or corrupted, another copy usually needs to be 

available in order to recover data and/or restore capabilities. At the same time, the more copies 

of a key that exist and are distributed to different locations, the more susceptible the key 

usually is to compromise through penetration of the storage location or subversion of the 

custodian (e.g., user, service agent, key production/distribution facility). In this sense, key 

confidentiality requirements conflict with continuity of operations requirements. Special care 

needs to be taken to safeguard all copies of keying material, especially symmetric keys and 

private (asymmetric) keys. More detail regarding contingency plans and planning requirements 

is provided in Part 2 of this Recommendation for Key Management [SP800-57, Part 2].

9.3.4 Compromise Recovery

When keying material that is used to protect sensitive information or critical processes is 

disclosed to unauthorized entities, all of the information and/or processes protected by that 

keying material becomes immediately subject to disclosure, modification, subversion, and/or 

denial of service. All compromised keys shall be revoked; all affected keys shall be replaced, 

if needed; and, where sensitive or critical information or processes are affected, an immediate 
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damage assessment should be conducted. Measures necessary to mitigate the consequences of 

suspected unauthorized access to protected data or processes and to reduce the probability or 

frequency of future compromises should be undertaken. 

Where symmetric keys or private (asymmetric) keys are used to protect only a single user’s 

local information or communications between a single pair of users, the compromise recovery 

process can be relatively simple and inexpensive. Damage assessment and mitigation measures 

are often local matters.

On the other hand, where a key is shared by or affects a large number of users, damage can be 

widespread, and recovery is both complex and expensive. Some examples of keys, the 

compromise of which might be particularly difficult or expensive to recover from, include the 

following:

1. A CA’s private signature key, especially if it is used to sign a root certificate in a 

public-key infrastructure;

2. A symmetric key-wrapping key shared by a large number of users;

3. A private asymmetric key-transport key shared by a large number of users;

4. A master key used in the derivation of keys by a large number of users;

5. A symmetric data-encryption key used to encrypt data in a large distributed database;

6. A symmetric key shared by a large number of communications network participants; 

and

7. A key used to protect a large number of stored keys.

In all of these cases, a large number of key owners or relying parties (e.g., all parties 

authorized to use the secret key of a symmetric-key algorithm or the public key of an 

asymmetric-key algorithm) would need to be immediately notified of the compromise. The 

inclusion of the key identifier on a Compromised Key List (CKL) or the certificate serial 

number on a Certificate Revocation List (CRL) to be published at a later date might not be 

sufficient. This means that a list of (the most-likely) affected entities might need to be 

maintained, and a means for communicating news of the compromise would be required. 

Particularly in the case of the compromise of a symmetric key, news of the compromise and 

the replacement of keys should be sent only to the affected entities so as not to encourage 

others to exploit the situation. 

In all of these cases, a secure path for replacing the compromised keys is required. In order to 

permit rapid restoration of service, an automated (e.g., over-the-air or network-based) 

replacement path is preferred (see Section 8.2.3). In some cases, however, there may be no 

practical alternative to manual distribution (e.g., the compromise of a root CA’s private key). A 

contingency distribution of alternate keys may help restore service rapidly in some 

circumstances (e.g., the compromise of a widely held symmetric key), but the possibility of a 

simultaneous compromise of operational and contingency keys would need to be considered.

Damage assessment can be extraordinarily complex, particularly in cases such as the 

compromise and replacement of CA private keys, widely used transport keys, and keys used by 

many users of large distributed databases.
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10 Key Management Specifications for Cryptographic Devices or 

Applications

Key management is often an afterthought in the cryptographic development process. As a 

result, cryptographic subsystems often fail to support the key-management functionality and 

protocols that are necessary to provide adequate security with the minimum necessary 

reduction in operational efficiency. All cryptographic development activities should involve 

key-management planning and specification (see [SP800-57, Part 2]) by those managers 

responsible for the secure implementation of cryptography into an information system. Keymanagement planning should begin during the initial conceptual/development stages of the 

cryptographic development lifecycle, or during the initial discussion stages for the application 

of existing cryptographic components into information systems and networks. The 

specifications that result from the planning activities shall be consistent with NIST keymanagement guidance (see [SP800-130] and [SP800152]).

For cryptographic development efforts, a key specification and acquisition planning process 

should begin as soon as the candidate algorithm(s) and, if appropriate, keying material media 

and format have been identified. Key-management considerations may affect algorithm choice, 

due to operational efficiency considerations for anticipated applications. For the application of 

existing cryptographic mechanisms for which no key-management specification exists, the 

planning and specification processes should begin during device and source selection, and 

continue through acquisition and installation. 

The types of key-management components that are required for a specific cryptographic device 

and/or for suites of devices used by organizations should be standardized to the maximum 

possible extent, and new cryptographic device-development efforts shall comply with NIST 

key-management recommendations. Accordingly, NIST criteria for the security, accuracy, and 

utility of key-management components in electronic and physical forms shall be met. Where 

the criteria for security, accuracy, and utility can be satisfied with standard key-management 

components (e.g., PKI), the use of those compliant components is encouraged. A developer 

may choose to employ non-compliant key management as a result of security, accuracy, utility, 

or cost considerations. However, such developments should conform as closely as possible to 

established key-management recommendations.

10.1 Key Management Specification Description/Purpose

The Key Management Specification is the document that describes the key-management 

components that may be required to operate a cryptographic device throughout its lifetime. 

Where applicable, the Key Management Specification also describes key-management 

components that are provided by a cryptographic device. The Key Management Specification 

documents the capabilities that the cryptographic application requires from key sources (e.g., 

the Key Management Infrastructure (KMI) described in Part 2 of this Recommendation for Key 

Management [SP800-57, Part 2]). 

10.2 Content of the Key Management Specification

The level of detail required for each section of the Key Management Specification can be 

tailored, depending upon the complexity of the device or application for which the Key 
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Management Specification is being written. The Key Management Specification should

contain a title page that includes the device identifier, and the developer’s or integrator’s 

identifier. A revision page, a list of reference documents, a table of contents, and a definition of 

abbreviations and acronyms page should also be included. The terminology used in a Key 

Management Specification shall be in accordance with the terms defined in appropriate NIST 

standards and guidelines. Unless the information is tightly controlled, the Key Management 

Specification should not contain proprietary or sensitive information. [Note: If the 

cryptographic application is supported by a PKI, a statement to that effect should be included 

in the appropriate Key Management Specification sections below.]

10.2.1 Cryptographic Application

A Cryptographic Application section provides a basis for the development of the rest of the 

Key Management Specification. The Cryptographic Application section provides a brief 

description of the cryptographic application or proposed employment of the cryptographic 

device. This includes the purpose or use of the cryptographic device (or application of a 

cryptographic device), and whether it is a new cryptographic device, a modification of an 

existing cryptographic device, or an existing cryptographic device for which a Key 

Management Specification does not exist. A brief description of the security services 

(confidentiality, integrity authentication, source authentication, non-repudiation support, access 

control, and availability) that the cryptographic device/application provides should be 

included. Information concerning long-term and potential interim key-management support 

(key-management components) for the cryptographic application should be provided.

10.2.2 Communications Environment

A Communications Environment section provides a brief description of the communications 

environment in which the cryptographic device is designed to operate. Some examples of 

communications environments include:

1. Data networks (e.g., intranet, Internet, VPN);

2. Wired communications (e.g., landline, dedicated or shared switching resources); and

3. Wireless communications (e.g., cell phones).

The environment may also include any anticipated access controls on communications 

resources, data sensitivity, privacy issues, etc. 

10.2.3 Key Management Component Requirements

A Key Management Component Requirements section describes the types and logical structure 

of the keying material required for the operation of the cryptographic device. Cryptographic 

applications using public-key certificates (e.g., X.509 certificates) should describe the types of 

certificates supported. The following information should be included:

1. The different keying material classes or types required, supported, and/or generated 

(e.g., for PKI: CA, signature, key establishment, and authentication);

2. The key management algorithm(s) (the applicable approved algorithms);

3. The keying material format(s) (reference any existing key specification, if known);

4. The set of acceptable PKI policies (as applicable); and
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5. The tokens to be used.

The description of the key-management component format may reference a key specification 

for an existing cryptographic device. If the format of the key-management components is not 

already specified, then the format and medium should be specified in the Key Management 

Specification.

10.2.4 Key Management Component Generation

The Key Management Specification should include a description of the requirements for the 

generation of key-management components by the cryptographic device for which the Key 

Management Specification is written. If the cryptographic device does not provide generation 

capabilities, the key-management components that will be required from external sources 

should be identified.

10.2.5 Key Management Component Distribution

When a device supports the automated distribution of keying material, the Key Management 

Specification should include a description of the distribution method(s) (where employed) 

used for keying material supported by the device. The distribution plan may describe the 

circumstances under which the key-management components are encrypted or in plaintext, 

their physical form (electronic, paper, etc.), and how they are identified during the distribution 

process. In the case of a dependence on manual distribution, the dependence and any handling 

assumptions regarding keying material should be stated.

10.2.6 Keying Material Storage

The Key Management Specification should address how the cryptographic device or 

application for which the Key Management Specification is being written stores information, 

and how the keying material is identified during its storage life (e.g., using a Distinguished 

Name). The storage capacity capabilities for information should be included.

10.2.7 Access Control

The Key Management Specification should address how access to the cryptographic device 

components and functions is to be authorized, controlled, and validated to request, generate, 

handle, distribute, store, and/or use keying material. Any use of passwords and personal 

identification numbers (PINs) should be included. For PKI cryptographic applications, role 

and identity-based privileging, and the use of any tokens should be described. 

10.2.8 Accounting

The Key Management Specification should describe any device or application support for the 

accounting of the keying material. Any support for or outputs to logs used to support the 

tracking of key-management component generation, distribution, storage, use and/or 

destruction should be detailed. The use of appropriate privileging to support the control of 

keying material that is used by the cryptographic application should also be described, in 

addition to the directory capabilities used to support PKI cryptographic applications, if 

applicable. The Key Management Specification shall identify where human and automated 

tracking actions are required and where multi-party control is required, if applicable. Section 

9.1 of this Recommendation provides accountability guidance.
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10.2.9 Compromise Management and Recovery

The Key Management Specification should address any support for the restoration of protected 

communications in the event of the compromise of keying material used by the cryptographic 

device/application. The recovery-process description should include the methods for rekeying. When used, the implementation of Certificate Revocation Lists (CRLs) and 

Compromised Key Lists (CKLs) should be detailed. For system specifications, a description of 

how certificates will be reissued and renewed within the cryptographic application should also 

be included. General compromise-recovery guidance is provided in Section 9.3.4 of this 

Recommendation.

10.2.10 Key Recovery

The Key Management Specification should include a description of product support or system 

mechanisms for effecting key recovery. Key recovery addresses how unavailable encryption 

keys can be recovered. System developers should include a discussion of the generation, 

storage, and access to long-term storage keys in the key-recovery-process description. The 

process of transitioning from the current to future long-term storage keys should also be 

described. General contingency planning guidance is provided in Section 9.3.3 of this 

Recommendation. Key recovery is treated in detail in Appendix B.
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APPENDIX A: Cryptographic and Non-cryptographic Integrity and 

Source Authentication Mechanisms

Integrity and source authentication services are particularly important in protocols that include 

key management. When integrity or source-authentication services are discussed in this 

Recommendation, they are afforded by “strong” cryptographic integrity or sourceauthentication mechanisms. Secure communications and key management are typically 

provided using a communication protocol that offers certain services, such as integrity

protection or a “reliable” transport service46. However, the integrity protection or reliable 

transport services of communication protocols are not necessarily adequate for cryptographic 

applications, particularly for key management, and there might be confusion about the meaning 

of terms such as “integrity.”

All communication channels have some noise (i.e., unintentional errors inserted by the 

transmission media), and other factors, such as network congestion, can cause network 

packets47 to be lost. Therefore, integrity protection and reliable transport services for 

communication protocols are designed to function over a channel with certain worst-case noise 

characteristics. Transmission bit errors are typically detected using 1) a non-cryptographic 

checksum48 to detect transmission errors in a packet, and 2) a packet counter that is used to 

detect lost packets. A receiving entity that detects damaged packets (i.e., packets that contain 

bit errors) or lost packets may request the sender to retransmit them. The non-cryptographic 

checksums are generally effective at detecting transmission noise. For example, the common 

CRC-32 checksum algorithm used in local-area network applications detects all error bursts 

with a span of less than 32 bits, and detects longer random bursts with a 2-32 failure probability. 

However, the non-cryptographic CRC-32 checksum does not detect the swapping of 32-bit 

message words, and specific errors in particular message bits cause predictable changes in the 

CRC-32 checksum. The sophisticated attacker can take advantage of this to create altered 

messages that pass the CRC-32 integrity checks, even, in some cases, when the message is 

encrypted. 

Forward error-correcting codes are a subset of non-cryptographic checksums that can be used 

to correct a limited number of errors without retransmission. These codes may be used as 

checksums, depending on the application and noise properties of the channel. 

Cryptographic integrity-authentication mechanisms (e.g., MACs or digital signatures), on the 

other hand, protect against an active, intelligent attacker who might attempt to disguise his 

attack as noise. Typically, the bits altered by the attacker are not random; they are targeted at 

system properties and vulnerabilities. Cryptographic integrity-authentication mechanisms are 

 46 A means of transmitting information within a network using protocols that provide assurances that the 

information is received correctly. 

47 A formatted unit of data used to send messages across a network. Messages may be divided into multiple 

packets for transmission efficiency.

48 Checksum: an algorithm that uses the bits in the transmission to create a checksum value. The checksum value 

is normally sent in the transmission. The receiver re-computes the checksum value using the bits in the received 

transmission, and compares the received checksum value with the computed value to determine whether or not the 

transmission was correctly received. A non-cryptographic checksum algorithm uses a well-known algorithm 

without secret information (i.e., a cryptographic key).
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effective in detecting random noise events, but they also detect the more systematic deliberate 

attacks. Cryptographic hash functions, such as SHA-256, are designed to make every bit of the 

hash value a complex, nonlinear function of every bit of the message text, and to make it 

impractical to find two messages that hash to the same value. On average, it is necessary to 

perform 2128 SHA-256 hash operations to find two messages that hash to the same value, and it 

is much harder to find another message whose SHA-256 hash is the same value as the hash of 

any given message. Cryptographic message authentication code (MAC) algorithms employ 

hash functions or symmetric encryption algorithms and keys to authenticate the source of a 

message and to protect the integrity of a message (i.e., to detect errors). Digital signatures use 

public-key algorithms and hash functions to provide both integrity and source-authentication 

services. Compared to non-cryptographic integrity or source-authentication mechanisms, these 

cryptographic services are usually computationally more expensive; this seems to be 

unavoidable, since cryptographic protections must also resist deliberate attacks by 

knowledgeable adversaries with substantial resources.

Cryptographic and non-cryptographic integrity-authentication mechanisms may be used 

together. For example, consider the TLS protocol (see [SP800-52]). In TLS, a client and a 

server can authenticate the identity of each other, establish a shared "master key" and transfer 

encrypted payload data. Every step in the entire TLS protocol run is protected by cryptographic 

integrity and source-authentication mechanisms, and the payload is usually encrypted. Like 

most cryptographic protocols, TLS will, with a given probability, detect any attack or noise 

event that alters any part of the protocol run. However, TLS has no error-recovery protocol. If 

an error is detected, the protocol run is simply terminated. Starting a new TLS protocol run is 

quite expensive. Therefore, TLS requires a “reliable” transport service, typically the Internet 

Transport Control Protocol (TCP), to handle and recover from ordinary network-transmission 

errors. TLS will detect errors caused by an attack or noise event, but has no mechanism to 

recover from them. TCP will generally detect such errors on a packet-by-packet basis and 

recover from them by retransmission of individual packets before delivering the data to TLS. 

Both TLS and TCP have integrity-authentication mechanisms, but a sophisticated attacker 

could easily fool the weaker non-cryptographic checksums of TCP. However, because of the 

cryptographic integrity-authentication mechanism provided in TLS, the attack is thwarted. 

There are some interactions between cryptographic and non-cryptographic integrity or errorcorrection mechanisms that users and protocol designers must take into account. For example, 

many encryption modes expand ciphertext errors: a single bit error in the ciphertext can change 

an entire block or more of the resulting plaintext. If forward error correction is applied before 

encryption, and errors are inserted in the ciphertext during transmission, the error expansion 

during the decryption might “overwhelm” the error-correction mechanism, making the errors 

uncorrectable. Therefore, it is preferable to apply the forward error-correction mechanism after 

the encryption process. This will allow the correction of errors by the receiving entity’s system 

before the ciphertext is decrypted, resulting in “correct” plaintext.

Interactions between cryptographic and non-cryptographic mechanisms can also result in 

security vulnerabilities. One classic way this occurs is with protocols that use stream ciphers49

 49 Stream ciphers encrypt and decrypt one element (e.g., bit or byte) at a time. There are no approved algorithms 

specifically designated as stream ciphers. However, some of the cryptographic modes defined in [SP 800-38] 

can be used with a symmetric block cipher algorithm, such as AES, to perform the function of a stream cipher.
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with non-cryptographic checksums (e.g. CRC-32) that are computed over the plaintext data 

and that acknowledge good packets. An attacker can copy the encrypted packet, selectively 

modify individual ciphertext bits, selectively change bits in the CRC, and then send the packet. 

Using the protocol’s acknowledgement mechanism, the attacker can determine when the CRC 

is correct, and therefore, determine certain bits of the underlying plaintext. At least one widely

used wireless-encryption protocol has been broken with such an attack.
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APPENDIX B: Key Recovery

Federal agencies have a responsibility to protect the information contained in, processed by 

and transmitted between their information technology systems. Cryptographic techniques are 

often used as part of this process. These techniques are used to provide confidentiality, 

integrity authentication, source authentication, non-repudiation support or access control. 

Policies shall be established to address the protection and continued accessibility of 

cryptographically protected information, and procedures shall be in place to ensure that the 

information remains viable during its lifetime. When cryptographic keying material is used to 

protect the information, this same keying material may need to be available to remove (e.g., 

decrypt) or verify (e.g., verify the MAC) those protections.

In many cases, the keying material used for cryptographic processes might not be readily 

available. This might be the case for several reasons, including:

1. The cryptoperiod of the key has expired, and the keying material is no longer in 

operational storage;

2. The keying material has been corrupted (e.g., the system has crashed or a virus has 

modified the saved keying material in operational storage); or

3. The owner of the keying material is not available, and the owner’s organization needs 

to obtain the plaintext information.

In order to have this keying material available when required, the keying material needs to be 

saved somewhere or to be constructible (e.g., derivable) from other available keying material. 

The process of re-acquiring the keying material is called key recovery. Key recovery is often 

used as one method of information recovery when the plaintext information needs to be 

recovered from encrypted information. However, keying material or other related information 

may need to be recovered for other reasons, such as the corruption of keying material in 

normal operational storage (see Section 8.2.1), e.g., the verification of MACs for archived 

documents. Key recovery may also be appropriate for situations in which it is easier or faster to 

recover the keying material than it is to generate and distribute new keying material. 

However, there are applications that may not need to save the keying material for an extended 

time because of other procedures to recover an operational capability when the keying material 

or the information protected by the keying material becomes inaccessible. Applications of this 

type could include telecommunications where the transmitted information could be resent, or 

applications that could quickly derive, or acquire and distribute new keying material.

It is the responsibility of an organization to determine whether or not the recovery of keying 

material is required for their application. The decision as to whether key recovery is required 

should be made on a case-by-case basis, and this decision should be reflected in the Key 

Management Policy and the Key Management Practices Statement (see [SP800-57, Part 2]). If 

the decision is made to provide key recovery, the appropriate method of key recovery should

be selected, designed and implemented, based on the type of keying material to be recovered; 

an appropriate entity needs to be selected to maintain the backup or archive database and 

manage the key-recovery process.

If the decision is made to provide key recovery for a key, all information associated with that 

key shall also be recoverable (see Table 5 in Section 6).
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B.1 Recovery from Stored Keying Material

The primary purpose of the back up or archiving of keying material is to be able to recover that 

material when it is not otherwise available. For example, encrypted information cannot be 

transformed back into plaintext information if the decryption key is lost or modified; the 

integrity of data cannot be authenticated if the key used to verify the integrity of that data is not 

available. The key-recovery process retrieves the keying material from backup or archive 

storage, and places it either in a device or module, or in other immediately accessible storage 

(see Section 8.3.1).

B.2 Recovery by Reconstruction of Keying Material

Some keying material may be recovered by reconstructing or re-deriving the keying material 

from other available keying material − the “base” keying material (e.g., a master key for a keyderivation method). The base keying material shall be available in normal operational storage 

(see Section 8.2.1), backup storage (see Section 8.2.2.1) or archive storage (see Section 8.3.1).

B.3 Conditions Under Which Keying Material Needs to be Recoverable 

The decision as to whether to back up or archive keying material for possible key recovery 

should be made on a case-by-case basis. The decision should be based on the list provided in 

Section 8.2.2.2.

When the key-recovery operation is requested by the key’s owner, the following actions shall

be taken: 

1. If a lost key may have been compromised, then the key shall be replaced as soon as 

possible after recovery in order to limit the exposure of the recovered key and the data 

it protects (see Section 8.2.3.1). This requires reapplying the protection on the protected 

data using the new key. For example, suppose that the key that was used to encrypt data

(KeyA) has been misplaced in a manner in which it could have been compromised. As 

soon as possible after KeyA is recovered, KeyA shall be used to decrypt the data, and the 

data shall be re-encrypted under a new key (KeyB). KeyB shall have no relationship to 

KeyA (e.g., KeyB shall not be an update of KeyA). 

2. If the key becomes inaccessible or has been modified, but compromise is not suspected, 

then the key may be recovered and used normally. No further action is required (e.g., 

re-encrypting the data). For example, if the key becomes inaccessible because the 

system containing the key crashes, or the key is inadvertently overwritten, and a 

compromise is not suspected, then the key may simply be restored.

The following subsections provide discussions to assist an organization in determining whether 

or not key recovery is needed. Although the following discussions address only the 

recoverability of keys, any related information (e.g., the metadata associated with the key) 

shall also be recoverable.

B.3.1 Signature Key Pairs

The private key of a signature key pair (the private signature key) is used by the owner of the 

key pair to apply digital signatures to information. The corresponding public key (the public 

signature-verification key) is used by relying entities to verify the digital signature.
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B.3.1.1 Private Signature Keys

Private signature keys shall not be archived (see Table 9 in Section 8.3.1). Key backup is not 

usually desirable for the private key of a signing key pair, since support for the nonrepudiability of the signature comes into question. However, exceptions may exist. For 

example, replacing the private signature key and having its corresponding public signatureverification key distributed (in accordance with Section 8.1.5.1) in a timely manner may not be 

possible under some circumstances, so recovering the private signature key from backup 

storage may be justified. This may be the case, for example, for the private signature key of a 

CA. 

If backup is considered for the private signature key, an assessment should be made as to its 

importance and the time needed to recover the key, as opposed to the time needed to generate a 

new key pair, and certify and distribute a new public signature-verification key. If a private 

signature key is backed up, the private signature key shall be recovered using a highly secure 

method. Depending on circumstances, the key should be recovered for immediate use only, 

and then shall be replaced as soon after the recovery process as possible. 

Instead of backing up the private signature key, a second private signature key and 

corresponding public key could be generated, and the public key distributed in accordance with 

Section 8.1.5.1 for use if the primary private signature key becomes unavailable. 

B.3.1.2 Public Signature-verification Keys

It is appropriate to backup or archive a public signature-verification key for as long as required 

in order to verify the information signed by the corresponding private signature key. In the case 

of a public key that has been certified (e.g., by a Certification Authority), saving the public-key 

certificate would be an appropriate form of storing the public key; backup or archive storage 

may be provided by the infrastructure (e.g., by a certificate repository). The public key should

be stored in backup storage until the end of the private key’s cryptoperiod, and should be 

stored in archive storage as long as required for the verification of signed data. 

B.3.2 Symmetric Authentication Keys

A symmetric authentication key is used to provide assurance of the integrity and source of 

information. A symmetric authentication key can be used:

1. By an originator to create a message authentication code (MAC) that can be verified at 

a later time to determine the integrity (and possibly the source) of the authenticated 

information; the authenticated information and its MAC could then be stored for later 

retrieval or transmitted to another entity,

2. By an entity that retrieves the authenticated information and the MAC from storage to 

determine the integrity of the stored information (Note: This is not a communication 

application),

3. Immediately upon receipt by a receiving entity to determine the integrity of transmitted 

information and the source of that information (the received MAC and the associated 

authenticated information may or may not be subsequently stored), or

4. By a receiving and retrieving entity to determine the integrity and source of information 

that has been received and subsequently stored using the same MAC (and the same 

authentication key); checking the MAC may not be performed prior to storage. 
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For each of the above cases, a decision to provide a key recovery capability should be made,

based on the following considerations.

In case 1, the symmetric authentication key need not be backed up or archived if the 

originator can establish a new authentication key prior to computing the MAC, making 

the key available to any entity that would need to subsequently verify the information 

that is authenticated using this new key. If a new authentication key cannot be obtained 

in a timely manner, then the authentication key should be backed up or archived.

In case 2, the symmetric authentication key should be backed up or archived for as 

long as the integrity and source of the information needs to be determined.

In case 3, the symmetric authentication key need not be backed up or archived if the 

authentication key can be resent to the recipient. In this case, establishing and 

distributing a new symmetric authentication key, rather than reusing the “lost” key, is 

also acceptable; a new MAC would need to be computed on the information using the 

new authentication key. Otherwise, the symmetric authentication key should be backed 

up. Archiving the authentication key is not appropriate if the MAC and the 

authenticated information are not subsequently stored, since the use of the key for both 

applying and checking the MAC would be discontinued at the end of the key's 

cryptoperiod. If the MAC and the authenticated information are subsequently stored, 

then the symmetric authentication key should be backed up or archived for as long as 

the integrity and source of the information needs to be determined. 

In case 4, the symmetric authentication key should be backed up or archived for as 

long as the integrity and source of the information needs to be determined. 

The symmetric authentication key may be stored in backup storage for the cryptoperiod of the 

key, and in archive storage until no longer required. If the authentication key is recovered by 

reconstruction, the “base” key (e.g., the master key for a key-derivation method) may be stored 

in normal operational storage or backup storage for the cryptoperiod of the base key, and in 

archive storage until no longer required.

B.3.3 Authentication Key Pairs

A public authentication key is used by a receiving entity to obtain assurance of the identity of 

the originating entity. The corresponding private authentication key is used by the originating 

entity to provide this assurance to a receiving entity by computing a digital signature on the 

information. This key pair may not provide support for non-repudiation.

B.3.3.1 Public Authentication Keys

It is appropriate to store a public authentication key in either backup or archive storage for as 

long as required to verify the identity of the entity that is participating in an authenticated 

communication session.

In the case of a public key that has been certified (e.g., by a Certification Authority), saving the 

public-key certificate would be an appropriate form of storing the public key; backup or 

archive storage may be provided by the infrastructure (e.g., by a certificate repository). The 

public key may be stored in backup storage until the end of the private key’s cryptoperiod, and 

may be stored in archive storage as long as required. 
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B.3.3.2 Private Authentication Keys

The private key is used to establish the identity of an entity who is participating in an 

authenticated communication session. The private authentication key need not be backed up if 

a new key pair can be generated and distributed in accordance with Section 8.1.5.1 in a timely 

manner. However, if a new key pair cannot be generated quickly, the private key should be 

stored in backup storage during the cryptoperiod of the private key. The private key shall not

be stored in archive storage.

B.3.4 Symmetric Data-Encryption Keys

A symmetric data-encryption key is used to protect the confidentiality of stored or transmitted 

information or both. The same key is used initially to encrypt the plaintext information to be 

protected, and later to decrypt the encrypted information (i.e., the ciphertext), thus obtaining 

the original plaintext.

The key needs to be available for as long as any information that is encrypted using that key 

may need to be decrypted. Therefore, the key should be backed up or archived during this 

period. 

In order to allow key recovery, the symmetric data-encryption key should be stored in backup 

storage during the cryptoperiod of the key, and should be stored in archive storage, if required. 

In many cases, the key is protected and stored with the encrypted data. When archived, the key 

is wrapped (i.e., encrypted) by an archive-encryption key or by a symmetric key-wrapping key 

that is wrapped by a protected archive-encryption key.

A symmetric-data encryption key that is used only for transmission is used by an originating 

entity to encrypt information, and by the receiving entity to decrypt the information 

immediately upon receipt. If the data-encryption key is lost or corrupted, and a new dataencryption key can be easily obtained by the originating and receiving entities, then the key 

need not be backed up. However, if the key cannot be easily replaced by a new key, then the 

key should be backed up if the information to be exchanged is of sufficient importance. The 

data-encryption key may not need to be archived when used for transmission only.

B.3.5 Symmetric Key-Wrapping Keys

A symmetric key-wrapping key is used to wrap (i.e., encrypt and integrity protect) keying 

material that is to be protected, and may be used to protect multiple sets of keying material. 

The protected keying material is then transmitted or stored or both. 

If a symmetric key-wrapping key is used only to transmit keying material, and the keywrapping key becomes unavailable (e.g., is lost or corrupted), it may be possible to either 

resend the key-wrapping key, or to establish a new key-wrapping key and use it to resend the 

keying material. If this is possible within a reasonable timeframe, backup of the key-wrapping

key is not necessary. If the key-wrapping key cannot be resent, or a new key-wrapping key 

cannot be readily obtained, backup of the key-wrapping key should be considered. The archive 

of a key-wrapping key that is only used to transmit keying material may not be necessary.

If a symmetric key-wrapping key is used to protect keying material in storage, then the keywrapping key should be backed up or archived for as long as the protected keying material 

may need to be accessed. 
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B.3.6 Random Number Generation Keys

A key used for random bit generation shall not be backed up or archived. If this key is lost or 

modified, it shall be replaced with a new key.

B.3.7 Symmetric Master Keys

A symmetric master key is normally used to derive one or more other keys. It shall not be used 

for any other purpose. 

The determination as to whether or not a symmetric master key needs to be backed up or 

archived depends on a number of factors:

1. How easy is it to establish a new symmetric master key? If the master key is distributed 

manually (e.g., in smart cards or in hard copy by receipted mail), the master key should

be backed up or archived. If a new master key can be easily and quickly established 

using automated key-establishment protocols, then the backup or archiving of the 

master key may not be necessary or desirable, depending on the application.

2. Are the derived keys recoverable without the use of the symmetric master key? If the 

derived keys do not need to be backed up or archived (e.g., because of their use) or 

recovery of the derived keys does not depend on reconstruction from the master key 

(e.g., the derived keys are stored in an encrypted form), then the backup or archiving of 

the master key may not be desirable. If the derived keys need to be backed up or 

archived, and the method of key recovery requires a reconstruction of the derived key 

from the master key, then the master key should be backed up or archived.

B.3.8 Key-Transport Key Pairs

A key-transport key pair may be used to transport keying material from an originating entity to 

a receiving entity during communications. The transported keying material could be stored in 

its encrypted form for decryption at a later time. The originating entity in a communication 

uses the public key to encrypt the keying material; the receiving entity (or the entity retrieving 

the stored keying material) uses the private key to decrypt the encrypted keying material.

B.3.8.1 Private Key-Transport Keys

If a key-transport key pair is used during communications without storing the encrypted keying 

material, then the private key-transport key does not need to be backed up if a replacement key 

pair can be generated and distributed in a timely fashion. Alternatively, one or more additional 

key pairs could be made available (i.e., already generated and distributed). Otherwise, the 

private key should be backed up. The private key-transport key may be archived.

If the transported keying material is stored in its encrypted form, then the private key-transport

key should be backed up or archived for as long as the protected keying material may need to 

be accessed. 

B.3.8.2 Public Key Transport Keys

Backup or archiving of the public key may be done, but may not be necessary.

If the sending entity (the originating entity in a communications) loses the public key-transport

key or determines that the key has been corrupted, the key can be reacquired from the key pair 
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owner or by obtaining the public-key certificate containing the public key (if the public key 

was certified). 

If the entity that applies the cryptographic protection to keying material that is to be stored 

determines that the public key-transport key has been lost or corrupted, the entity may recover 

in one of the following ways:

1. If the public key has been certified and is stored elsewhere within the infrastructure, 

then the certificate can be requested;

2. If some other entity knows the public key (e.g., the owner of the key pair), the key can 

be requested from this other entity;

3. If the private key is known, then the public key can be recomputed; or

4. A new key pair can be generated.

B.3.9 Symmetric Key Agreement Keys

Symmetric key-agreement keys are used to establish keying material (e.g., symmetric keywrapping keys, symmetric data-encryption keys, or symmetric authentication keys). Each keyagreement key is shared between two or more entities. If these keys are distributed manually 

(e.g., in a key-loading device or by receipted mail), then the symmetric key-agreement key 

should be backed up. If an automated means is available for quickly establishing new keys 

(e.g., a key-transport mechanism can be used to establish a new symmetric key-agreement

key), then a symmetric key-agreement key need not be backed up. 

Symmetric key-agreement keys may be archived.

B.3.10 Static Key-Agreement Key Pairs

Static key-agreement key pairs are used to establish shared secrets between entities (see 

[SP800-56A] and [SP800-56B]), sometimes in conjunction with ephemeral key pairs (see 

[SP800-56A]). Each entity uses its private key-agreement key(s), the other entity's public keyagreement key(s) and possibly its own public key-agreement key(s) to determine the shared 

secret. The shared secret is subsequently used to derive shared keying material. Note that in 

some key-agreement schemes, one or more of the entities may not use a static key-agreement

pair (see [SP800-56A] and [SP800-56B]).

B.3.10.1 Private Static Key-Agreement Keys

If the private static key-agreement key cannot be replaced in a timely manner, or if it needs to 

be retained in order to recover encrypted stored data, then the private key should be backed up 

in order to continue operations. The private key may be archived.

B.3.10.2 Public Static Key Agreement Keys

If an entity determines that the public static key-agreement key is lost or corrupted, the entity 

may recover in one of the following ways:

1. If the public key has been certified and is stored elsewhere within the infrastructure, 

then the certificate can be requested;

2. If some other entity knows the public key (e.g., the other entity is the owner of the key 

pair), the key can be requested from this other entity;
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3. If the private key is known, then the public key can be recomputed; or

4. If the entity is the owner of the key pair, a new key pair can be generated and 

distributed.

If none of these alternatives are possible, then the public static key-agreement key should be 

backed up. The public key may be archived.

B.3.11 Ephemeral Key Pairs

Ephemeral key-agreement keys are generated and distributed during a single key-agreement

transaction (e.g., at the beginning of a communication session) and are not reused. These key 

pairs are used to establish a shared secret (often in combination with static key pairs); the 

shared secret is subsequently used to derive shared keying material. Not all key-agreement

schemes use ephemeral key pairs, and when used, not all entities have an ephemeral key pair 

(see [SP800-56A]).

B.3.11.1 Private Ephemeral Keys

Private ephemeral keys shall not50 be backed up or archived. If the private ephemeral key is 

lost or corrupted, a new key pair shall be generated, and the new public ephemeral key shall be 

provided to the other participating entity in the key-agreement process.

B.3.11.2 Public Ephemeral Keys

Public ephemeral keys may be backed up or archived. This may allow the reconstruction of the 

established keying material, as long as the private ephemeral keys are not required in the keyagreement computation. 

B.3.12 Symmetric Authorization Keys

Symmetric authorization keys are used to provide privileges to an entity (e.g., access to certain 

information or authorization to perform certain functions). The loss of these keys will deny the 

privileges (e.g., prohibit access and disallow the performance of these functions). If the 

authorization key is lost or corrupted and can be replaced in a timely fashion, then the 

authorization key need not be backed up. A symmetric authorization key shall not be archived.

B.3.13 Authorization Key Pairs

Authorization key pairs are used to determine the privileges that an entity may assume. The 

private key is used to establish the "right" to the privilege; the public key is used to determine 

that the entity actually has the right to the privilege.

B.3.13.1 Private Authorization Keys

The loss of the private authorization key will deny privileges (e.g., prohibit access and disallow 

the performance of certain functions requiring authorization). If the private key is lost or 

corrupted and can be replaced in a timely fashion, then the private key need not be backed up. 

Otherwise, the private key should be backed up. The private key shall not be archived.

 50 SP 800-56A states that the private ephemeral keys shall be destroyed immediately after use. This implies that 

the private ephemeral keys shall not be backed up or archived.
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B.3.13.2 Public Authorization Keys

If the authorization key pair can be replaced in a timely fashion (i.e., by a regeneration of the 

key pair and secure distribution of the private key to the entity seeking authorization), then the 

public authorization key need not be backed up. Otherwise, the public key should be backed 

up. There is no restriction about archiving the public key. 

B.3.14 Other Cryptographically Related Material

Like keys, other cryptographically related material may need to be backed up or archived, 

depending on its use.

B.3.14.1 Domain Parameters

Domain parameters are used in conjunction with some public key algorithms to generate key 

pairs. They are also used with key pairs to create and verify digital signatures or to establish 

keying material. The same set of domain parameters is often, but not always, used by a large 

number of entities.

When an entity (entity A) generates new domain parameters, these domain parameters are used 

in subsequent digital signature generation or key-establishment processes. The domain 

parameters need to be provided to other entities that need to verify the digital signatures or 

with whom keys will be established. If the entity (entity A) determines that its copies of the 

domain parameters have been lost or corrupted, and if the new domain parameters cannot be 

securely distributed in a timely fashion, then the domain parameters should be backed up or 

archived. 

When the same set of domain parameters are used by multiple entities, the domain parameters 

should be backed up or archived until no longer required unless the domain parameters can be 

otherwise obtained (e.g., from a trusted source).

B.3.14.2 Initialization Vectors (IVs)

IVs are used by several modes of operation during the encryption or authentication of 

information using block cipher algorithms. IVs are often stored with the data that they protect. 

If not stored with the data, IVs should be backed up or archived as long as the information 

protected using those IVs needs to be processed (e.g., decrypted or authenticated).

B.3.14.3 Shared Secrets

Shared secrets are generated by each entity participating in a key-agreement process. The 

shared secret is then used to derive the shared keying material to be used in subsequent 

cryptographic operations. Shared secrets may be generated during interactive communications 

(e.g., where both entities are online) or during non-interactive communications (e.g., in store 

and forward applications).

A shared secret shall not be backed up or archived.

B.3.14.4 RBG Seeds

RBG seeds are used for the generation of random bits and need to remain secret. These seeds 

shall not be shared with other entities. RBG seeds shall not be backed up or archived.
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B.3.14.5 Other Public and Secret Information

Public and secret information is often used during key establishment. The information may 

need to be available to determine the keys that are needed to process cryptographically 

protected information (e.g., to decrypt or authenticate); therefore, the information should be 

backed up or archived until no longer needed to process the protected information.

B.3.14.6 Intermediate Results

The intermediate results of a cryptographic operation shall not be backed up or archived. 

B.3.14.7 Key Control Information

Key control information is used, for example, to determine the keys and other information to 

be used to process cryptographically protected information (e.g., decrypt or authenticate), to 

identify the purpose of a key, or to identify the entities that share the key (see Section 6.2.3).

This information is contained in the key’s metadata (see Section 6.2.3.1).

Key control information should be backed up or archived for as long as the associated key 

needs to be available.

B.3.14.8 Random Numbers

Random numbers are generated by random number generators. The backup or archiving of a 

random number depends on how it is used. 

B.3.14.9 Passwords

A password is used to acquire access to privileges by an entity, to derive keys or to detect the 

re-use of passwords.

If the password is only used to acquire access to privileges, and can be replaced in a timely 

fashion, then the password need not be backed up. In this case, a password shall not be 

archived.

If the password is used to derive cryptographic keys or to prevent the re-use of passwords, the 

password should be backed up and archived.

B.3.14.10 Audit Information

Audit information containing key-management events shall be backed up and archived.

B.4 Key Recovery Systems

Key recovery is a broad term that may be applied to several different key-recovery techniques. 

Each technique will result in the recovery of a cryptographic key and other information 

associated with that key (e.g., the key's metadata). The information required to recover that key 

may be different for each application or each key-recovery technique. The term “Key Recovery 

Information” (KRI) is used below to refer to the aggregate of information that is needed to 

recover or verify cryptographically protected information. Information that may be considered 

as KRI includes the keying material to be recovered or sufficient information to reconstruct the 

keying material, other associated cryptographic information, the time when the key was 

created, the identifier associated with the owner of the key (i.e., the individual, application or 

organization that created the key or that owns the data protected by that key) and any 

conditions that must be met by a requestor to be able to recover the keying material.
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When an organization determines that key recovery is required for all or part of its keying 

material, a secure Key Recovery System (KRS) needs to be established in accordance with a 

well-defined Key Recovery Policy (see Appendix B.5). The KRS shall support the Key 

Recovery Policy and consists of the techniques and facilities for saving and recovering the 

keying material, the procedures for administering the system, and the personnel associated with 

the system. 

When key recovery is determined to be necessary, the KRI may be stored either within an 

organization (in backup or archive storage) or may be stored at a remote site by a trusted entity. 

There are many acceptable methods for enabling key recovery. A KRS could be established 

using a safe for keying material storage; a KRS might use a single computer that provides the 

initial protection of the plaintext information, storage of the associated keying material and 

recovery of that keying material; a KRS may include a network of computers with a central 

Key Recovery Center; or a KRS could be designed using other configurations. Since a KRS 

provides a means for recovering cryptographic keys, a risk assessment should be performed to 

ensure that the KRS adequately protects the organization’s information and reliably provides 

the KRI when required. It is the responsibility of the organization that needs to provide key 

recovery to ensure that the Key Recovery Policy, the key recovery methodology, and the Key 

Recovery System adequately protect the KRI.

A KRS used by the Federal government shall:

1. Generate or provide sufficient KRI to allow recovery or verification of protected 

information when such information has been stored;

2. Ensure the validity of the saved key and the other KRI;

3. Ensure that the KRI is stored with persistence and availability that is commensurate 

with that of the corresponding cryptographically protected data;

4. Use cryptographic modules that are compliant with [FIPS140];

5. Use approved algorithms, when cryptography is used;

6. Use algorithms and key lengths that provide security strengths commensurate with the 

sensitivity of the information associated with the KRI; 

7. Be designed to enforce the Key Recovery Policy (see Appendix B.5);

8. Protect KRI against unauthorized disclosure or destruction; the KRS shall verify the 

source of requests and ensure that only requested and authorized information is 

provided to the requestor;

9. Protect the KRI from modification;

10. Have the capability of providing an audit trail; the audit trail shall not contain the keys 

that are recovered or any passwords that may be used by the system; the audit trail 

should include the identification of the event being audited, the time of the event, the 

identifier associated with the user causing the event, and the success or failure of the 

event;

11. Limit access to the KRI, the audit trail and authentication data to authorized 

individuals; and
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12. Prohibit modification of the audit trail.

B.5 Key Recovery Policy

For each system, application and cryptographic technique used, consideration shall be given as 

to whether or not the keying material may need to be saved for later recovery to allow 

subsequent decryption or checking the information protected by the keying material. An 

organization that determines that key recovery is required for some or all of its keying material 

should develop a Key Recovery Policy that addresses the protection and continued 

accessibility of that information51 (see [DOD-KRP]). The policy should answer the following 

questions (at a minimum):

1. What keying material needs to be saved for a given application? For example, keys and 

IVs used for the decryption of stored information may need to be saved. Keys for the 

authentication of stored or transmitted information may also need to be saved. 

2. How and where will the keying material be saved? For example, the keying material 

could be stored in a safe by the individual who initiates the protection of the 

information (e.g., the encrypted information), or the keying material could be saved 

automatically when the protected information is transmitted, received or stored. The 

keying material could be saved locally or at some remote site.

3. Who will be responsible for protecting the KRI? For example, each individual, 

organization or sub-organization could be responsible for their own keying material, or 

an external organization could perform this function.

4. Who is authorized to receive the KRI upon request and under what conditions? For 

example, the individual who protected the information (i.e., used and stored the KRI) or 

the organization to which the individual is assigned could recover the keying material. 

Legal requirements may need to be considered. An organization could request the 

information when the individual who stored the KRI is not available. 

5. Under what conditions can the policy be modified and by whom?

6. What audit capabilities and procedures will be included in the KRS? The policy shall

identify the events to be audited. Auditable events might include KRI requests and their 

associated responses; who made a request and when; the startup and shutdown of audit 

functions; the operations performed to read, modify or destroy the audit data; requests 

to access user authentication data; and the uses of authentication mechanisms.

7. How will the KRS deal with aged keying material whose security strength is now 

reduced beyond an acceptable level?

8. Who will be notified when keying material is recovered and under what conditions? 

For example, the individual who encrypted data and stored the KRI could be notified 

when the organization recovers the decryption key because the person is absent, but the 

individual might not be notified when the organization is monitoring the activities of 

that individual.

 51 An organization’s key recovery policy may be included in its PKI Certificate Policy.
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9. What procedures need to be followed when the KRS or some portion of the data within 

the KRS is compromised?
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APPENDIX C: References

[AC] Schneier, B. Applied Cryptography Second Edition: Protocols, 

Algorithms, and Source Code in C. New York: John Wiley & Sons, 

1996.

[ANSX9.31] American National Standards Institute, Digital Signatures using 

reversible Public Key Cryptography for the Financial Services Industry 

(rDSA), ANS X9.31-1998, 1998 [Withdrawn].

[ANSX9.44] American National Standards Institute, Public Key Cryptography for the 

Financial Services Industry: Key Agreement Using Integer Factorization

Cryptography, ANS X9.44, August 2007.

[ANSX9.62] American National Standards Institute, Public Key Cryptography for the 

Financial Services Industry: the Elliptic Curve Digital Signature 

Algorithm (ECDSA), ANS X9.62:2005, 2005.

[DiCrescenzo] Di Crescenzo, G., N. Ferguson, R. Impagliazzo, and M Jakobsson, 

“How to forget a secret,” in STACS 99: 16th Annual Symposium on 

Theoretical Aspects of Computer Science, Lecture Notes in Computer 

Science 1563, 1999, pp. 500-509. http://dx.doi.org/10.1007/3-540-

49116-3_47. 

[DOD-KRP] DoD Public Key Infrastructure Program Management Office, Key 

Recovery Policy for the United States Department of Defense, Version 

3.0, August 31, 2003.

[FIPS140] Federal Information Processing Standard 140-2, Security Requirements 

for Cryptographic Modules, May 25, 2001 (include change notices as of 

December 3, 2002). http://csrc.nist.gov/publications/fips/fips140-

2/fips1402.pdf [accessed 12/7/15].

[FIPS180] Federal Information Processing Standard 180-4, Secure Hash Standard 

(SHS), August 2015. http://dx.doi.org/10.6028/NIST.FIPS.180-4.

[FIPS186] Federal Information Processing Standard 186-4, Digital Signature 

Standard (DSS), July 2013. http://dx.doi.org/10.6028/NIST.FIPS.186-4.

[FIPS197] Federal Information Processing Standard 197, Advanced Encryption 

Standard (AES), November 2001.

http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf [accessed 

12/7/15]. 

[FIPS198] Federal Information Processing Standard 198-1, The Keyed-Hash 

Message Authentication Code (HMAC), July 2008.

http://csrc.nist.gov/publications/fips/fips198-1/FIPS-198-1_final.pdf

[accessed 12/7/15].

[FIPS199] Federal Information Processing Standard 199, Standards for Security 

Categorization of Federal Information and Information Systems,
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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February 2004. http://csrc.nist.gov/publications/fips/fips199/FIPS-PUB199-final.pdf [accessed 12/7/15].

[FIPS201] Federal Information Processing Standard 201-2, Personal Identity 

Verification (PIV) of Federal Employees and Contractors, August 2013.

http://dx.doi.org/10.6028/NIST.FIPS.201-2.

[FIPS202] Federal Information Processing Standard 202, SHA-3 Standard: 

Permutation-Based Hash and Extendable-Output Functions, August 

2015. http://dx.doi.org/10.6028/NIST.FIPS.202.

[HAC] Menezes, A. J., P. C. van Ooorschot, and S. A. Vanstone, Handbook of 

Applied Cryptography, Washington, D.C.: CRC Press, 1996.

[ITLBulletin] Burr, B. and J. Hash, “Techniques for System and Data Recovery,” ITL 

Bulletin, NIST, April 2002. http://csrc.nist.gov/publications/nistbul/04-

02.pdf [accessed 12/7/15].

[OMB11/01] OMB Guidance to Federal Agencies on Data Availability and 

Encryption, Office of Management and Budget, [November 26, 2001].

http://csrc.nist.gov/drivers/documents/ombencryption-guidance.pdf

[accessed 12/7/15].

[PKCS#1] RSA Laboratories, PKCS #1 v2.1, RSA Cryptography Standard, June 14, 

2002.

[RFC2560] Myers, M., R. Ankney, A. Malpani, S. Galperin, and C. Adams, X.509 

Internet Public Key Infrastructure, Online Certificate Status Protocol –

OCSP, Internet Engineering Task Force (IETF) Request for Comments 

(RFC) 2560, June 1999. https://www.ietf.org/rfc/rfc2560.txt [accessed 

12/7/15].

[SP800-14] NIST Special Publication 800-14, Generally Accepted Principles and 

Practices for Securing Information Technology Systems, September 

1996. http://csrc.nist.gov/publications/nistpubs/800-14/800-14.pdf

[accessed 12/7/15].

[SP800-21] NIST Special Publication 800-21 [Second Edition], Guideline for 

Implementing Cryptography in the Federal Government, December 

2005. http://csrc.nist.gov/publications/nistpubs/800-21-1/sp800-21-

1_Dec2005.pdf [accessed 12/7/15].

[SP800-32] NIST Special Publication 800-32, Introduction to Public Key 

Technology and the Federal PKI Infrastructure, February 2001.

http://csrc.nist.gov/publications/nistpubs/800-32/sp800-32.pdf [accessed 

12/7/15].

[SP800-37] NIST Special Publication 800-37 Revision 1, Guide for Applying the 

Risk Management Framework to Federal Information Systems: a 

Security Life Cycle Approach, February 2010 (updated June 5, 2014).

http://dx.doi.org/10.6028/NIST.SP.800-37r1. 
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[SP800-38] NIST Special Publication 800-38, Recommendation for Block Cipher 

Modes of Operation, consists of the following parts, which are further 

described at http://csrc.nist.gov/groups/ST/toolkit/BCM/index.html 

[accessed 12/7/15]: 

NIST SP 800-38A, Methods and Techniques, December 2001.

NIST SP 800-38A (Addendum), Three Variants of Ciphertext Stealing 

for CBC Mode, October 2010.

NIST SP 800-38B, The CMAC Mode for Authentication, May 2005.

NIST SP 800-38C, The CCM Mode for Authentication and 

Confidentiality, May 2004 (updated July 20, 2007).

NIST SP 800-38D, Galois/Counter Mode (GCM) and GMAC, 

November 2007.

NIST SP 800-38E, The XTS-AES Mode for Confidentiality on Storage 

Devices, January 2010.

NIST SP 800-38F, Methods for Key Wrapping, December 2012.

NIST SP 800-38G (Draft), Methods for Format-Preserving Encryption, 

July 2013.

[SP800-38A] NIST Special Publication 800-38A, Recommendation for Block Cipher 

Modes of Operation: Methods and Techniques, December 2001.

http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf

[accessed 12/7/15].

[SP800-38B] NIST Special Publication 800-38B, Recommendation for Block Cipher 

Modes of Operation: The CMAC Mode for Authentication, May 2005.

http://csrc.nist.gov/publications/nistpubs/800-38B/SP_800-38B.pdf

[accessed 12/7/15].

[SP800-38D] NIST Special Publication 800-38D, Recommendation for Block Cipher 

Modes of Operation: Galois/Counter Mode (GCM) and GMAC, 

November 2007. http://csrc.nist.gov/publications/nistpubs/800-38D/SP800-38D.pdf [accessed 12/7/15].

[SP800-38F] NIST Special Publication 800-38F, Recommendation for Block Cipher 

Modes of Operation: Methods for Key Wrapping, December 2012.

http://dx.doi.org/10.6028/NIST.SP.800-38F. 

[SP800-52] NIST Special Publication 800-52 Revision 1, Guidelines for the 

Selection, Configuration, and Use of Transport Layer Security (TLS) 

Implementations, April 2014. http://dx.doi.org/10.6028/NIST.SP.800-

52r1. 

[SP800-56A] NIST Special Publication 800-56A Revision 2, Recommendation for 

Pair-Wise Key Establishment Schemes Using Discrete Logarithm 

Cryptography, May 2013. http://dx.doi.org/10.6028/NIST.SP.800-

56Ar2. 
NIST SP 800-57 Pt. 1 Rev. 4 Recommendation for

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[SP800-56B] NIST Special Publication 800-56B Revision 1, Recommendation for 

Pair-Wise Key Establishment Schemes Using Integer Factorization 

Cryptography, September 2014. http://dx.doi.org/10.6028/NIST.SP.800-

56Br1. 

[SP800-56C] NIST Special Publication 800-56C, Recommendation for Key Derivation 

through Extraction-then-Expansion, November 2011.

http://csrc.nist.gov/publications/nistpubs/800-56C/SP-800-56C.pdf

[accessed 12/7/15].

[SP800-57, Part 2] NIST Special Publication 800-57 Part 2, Recommendation for Key 

Management: Part 2: Best Practices for Key Management 

Organization, August 2005.

http://csrc.nist.gov/publications/nistpubs/800-57/SP800-57-Part2.pdf

[accessed 12/7/15].

[SP800-63] NIST Special Publication 800-63-2, Electronic Authentication 

Guideline, August 2013. http://dx.doi.org/10.6028/NIST.SP.800-63-2. 

[SP800-67] NIST Special Publication 800-67 Revision 1, Recommendation for 

Triple Data Encryption Algorithm (TDEA) Block Cipher, January 2012.

http://csrc.nist.gov/publications/nistpubs/800-67-Rev1/SP-800-67-

Rev1.pdf [accessed 12/7/15].

[SP 800-88] NIST Special Publication 800-88 Revision 1, Guidelines for Media 

Sanitization, December 2014. http://dx.doi.org/10.6028/NIST.SP.800-

88r1.

[SP800-89] NIST Special Publication 800-89, Recommendation for Obtaining 

Assurances for Digital Signature Applications, November 2006.

http://csrc.nist.gov/publications/nistpubs/800-89/SP-800-

89_November2006.pdf [accessed 12/7/15].

[SP800-90] Joint reference to [SP800-90A], [SP800-90B], and [SP800-90C].

[SP800-90A] NIST Special Publication 800-90A Revision 1, Recommendation for 

Random Number Generation Using Deterministic Random Bit 

Generators,June 2015. http://dx.doi.org/10.6028/NIST.SP.800-90Ar1. 

[SP800-90B] NIST Special Publication 800-90B (Draft), Recommendation for the 

Entropy Sources Used for Random Bit Generation, August 2012 [reissued September 9, 2013]. http://csrc.nist.gov/publications/drafts/800-

90/draft-sp800-90b.pdf [accessed 12/7/15].

[SP800-90C] NIST Special Publication 800-90C (Draft), Recommendation for 

Random Bit Generator (RBG) Constructions, August 2012 [re-issued 

September 9, 2013. http://csrc.nist.gov/publications/drafts/800-90/draftsp800-90c.pdf [accessed 12/7/15].

[SP800-107] NIST Special Publication 800-107 Revision 1, Recommendation for 

Applications Using Approved Hash Algorithms, August 2012.

http://csrc.nist.gov/publications/nistpubs/800-107-rev1/sp800-107-

rev1.pdf [accessed 12/7/15].
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[SP800-108] NIST Special Publication 800-108, Recommendation for Key Derivation 

Using Pseudorandom Functions, October 2009.

http://csrc.nist.gov/publications/nistpubs/800-108/sp800-108.pdf

[accessed 12/7/15].

[SP800-130] NIST Special Publication 800-130, A Framework for Designing 

Cryptographic Key Management Systems, August 2013.

http://dx.doi.org/10.6028/NIST.SP.800-130.

[SP800-131A] NIST Special Publication 800-131A Revision 1, Transition: 

Recommendation for Transitioning the Use of Cryptographic Algorithms 

and Key Lengths, November 2015.

http://dx.doi.org/10.6028/NIST.SP.800-131Ar1. 

[SP800-132] NIST Special Publication 800-132, Recommendation for PasswordBased Key Derivation - Part 1: Storage Applications, December 2010.

http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf

[accessed 12/7/15].

[SP800-133] NIST Special Publication 800-133, Recommendation for Cryptographic 

Key Generation, December 2012.

http://dx.doi.org/10.6028/NIST.SP.800-133. 

[SP800-152] NIST Special Publication 800-152, A Profile for U. S. Federal 

Cryptographic Key Management Systems (CKMS), October 2015.

http://dx.doi.org/10.6028/NIST.SP.800-152. 
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APPENDIX D: Revisions

The original version of this document was published in August 2005. In May 2006, the 

following revisions were incorporated:

1. The definition of security strength has been revised to remove “or security level” 

from the first column, since this term is not used in the document.

2. In the footnote for 2TDEA in Table 2 of Section 5.6.1, the word “guarantee” has 

been changed to “assessment”.

3. In the paragraph under Table 2 in Section 5.6.1: The change originally identified 

for the 2006 revision has been superseded by the 2011 revision discussed below.

4. In Table 3 of Section 5.6.1, a list of appropriate hash functions have been inserted 

into the HMAC and Key Derivation Function columns. In addition, a footnote has 

been included for the Key Derivation Function column.

5. The original text for the paragraph immediately below Table 3 has been removed.

In March 2007, the following revisions were made to allow the dual use of keys during 

certificate requests:

1. In Section 5.2, the following text was added:

“This Recommendation also permits the use of a private key-transport or keyagreement private key to generate a digital signature for the following special 

case:

When requesting the (initial) certificate for a static key-establishment key, 

the associated private key may be used to sign the certificate request. Also 

refer to Section 8.1.5.1.1.2.”

2. In Section 8.1.5.1.1.2, the fourth paragraph was originally as follows:

“The owner provides POP by performing operations with the private key that 

satisfy the indicated key use. For example, if a key pair is intended to support 

key transport, the owner may decrypt a key provided to the owner by the CA 

that is encrypted using the owner's public key. If the owner can correctly 

decrypt the ciphertext key using the associated private key and then provide 

evidence that the key was correctly decrypted (e.g., by encrypting a random 

challenge from the CA, then the owner has established POP. Where a key pair 

is intended to support key establishment, POP shall not be afforded by 

generating and verifying a digital signature with the key pair.”

The paragraph was changed to the following, where the changed text is indicated 

in italics:

“The (reputed) owner should provide POP by performing operations with the 

private key that satisfy the indicated key use. For example, if a key pair is 

intended to support RSA key transport, the CA may provide the owner with a 

key that is encrypted using the owner's public key. If the owner can correctly 

decrypt the ciphertext key using the associated private key and then provide 

evidence that the key was correctly decrypted (e.g., by encrypting a random 
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challenge from the CA, then the owner has established POP. However, when a 

key pair is intended to support key establishment, POP may also be afforded 

by using the private key to digitally sign the certificate request (although this 

is not the preferred method). The private key establishment private key (i.e., 

the private key-agreement or key-transport key) shall not be used to perform 

signature operations after certificate issuance.”

In September 2011, several editorial corrections and clarifications were made, and the 

following revisions were also made:

1. The Authority section has been updated.

2. Section 1.2: The description of SP800-57, Part 3 has been modified per that 

document.

3. Section 2.1: Definitions for key-derivation function, key-derivation key, key 

length, key size, random bit generator and user were added. Definitions for 

archive, key management archive, key recovery, label, owner, private key, proof 

of possession, public key, security life of data, seed, shared secret and should

have been modified. The definition for cryptomodule was removed.

4. Section 2.2: The RBG acronym was inserted.

5. References to FIPS 180-3, FIPS 186-3, SP 800-38, SP 800-56A, SP 800-56B, SP 

800-56C, SP 800-89, SP 800-90, SP 800-107, SP 800-108, SP 800-131A, SP 800-

132 and SP 800-133 have been corrected or inserted.

6. Section 4.2.4: A footnote was added about the two general types of digital 

signatures and the focus for this Recommendation.

7. Sections 4.2.5, 4.2.5.3, 4.2.5.5 and 5.3: Discussions about SP 800-56B have been

included.

8. Section 5.1.1: The definitions of private signature key, public signatureverification key, symmetric authentication key, private authentication key and 

public authentication key have been corrected to reflect their current use in 

systems and protocols. This change is reflected throughout the document.

9. Section 5.1.2, item 3: The description of shared secret has been modified to state 

that shared secrets are to be protected and handled as if they are cryptographic 

keys.

10. Sections 5.1.2, 5.3.7, 6.1.2 (Table 5), 8.1.5.3.4, 8.1.5.3.5, 8.2.2.1 (Table 7) and 

8.3.1 (Table 9): “Other secret information” has been added to the list of other 

cryptographic or related information. 

11. Section 5.3.1: An additional risk factor was inserted about personnel turnover.
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12. Section 5.3.4: A statement was inserted to clarify the difference between the 

cryptoperiod of a public key and the validity period of a certificate.

13. Section 5.3.6: Statements were inserted that emphasize that longer or shorter 

cryptoperiods than those suggested may be warranted. Also, further discussion 

was added about the cryptoperiod of the public ephemeral key-agreement key.

14. Section 5.4.4: A discussion of an owner’s assurance of private-key possession 

was added.

15. Section 5.5: Statements were added about the compromise of a CA’s private 

signature key, and advice was provided for handling such an event.

16. Section 5.6.1: Table 3 and the text preceding the table have been revised for 

clarity. Additional footnotes were inserted related to table entries, and the 

footnote about the security strength provided by SHA-1 was modified to indicate 

that its security strength for digital signature applications remains the subject of 

speculation.

17. Sections 5.6.2 – 5.6.4: Table 4 and the text preceding it have been modified to be 

consistent with SP 800-131A. Also, the examples have been modified.

18. Section 5.6.5: This new section was added to address the implications associated 

with the reduction of security strength because of improvements in computational 

capabilities or cryptanalysis. 

19. Sections 7, 7.1, 7.2 and 7.3: The description of the states and their transitions have 

been reworded to require specific behavior (e.g., using shall or shall not

statements, rather than containing statement of fact (e.g., using “is” or are”). 

20. Section 7.3: A discussion of the transition of a private key-transport key and an 

ephemeral private key-agreement key were added. The previous discussion on 

private and public key-agreement keys was changed to discuss static private and 

public key-agreement keys and ephemeral public key-agreement keys. 

21. Section 8.1.5.3.4: This section was revised to be more consistent with SP 800-

90A.

22. Sections 8.1.5.3.7 and 8.1.5.3.8: New sections were inserted to discuss the 

distribution of random numbers and passwords.

23. Section 8.1.6: Text was inserted to indicate which keys would or would not be 

registered.

24. Section 8.2.4: This section was revised to be consistent with SP 800-56A SP 800-

56B, SP 800-56C, SP 800-108 and SP 800-132.
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25. Section 8.3.1, Table 9: The table was modified to indicate that it is OK to archive 

the static key-agreement key.

26. Changes were made to Sections 8.3.1; 9.3.2; and Appendices B, B.1, B.3, B.3.1.2, 

B.3.2, B.3.4, B.3.5, and B.3.10.2 to remove the impression that archiving is only 

performed after the end of the cryptoperiod of a key (e.g., keys could be archived 

immediately upon activation), and that the keys in an archive are only of historical 

interest (e.g., they may be needed to decrypt data long after the cryptoperiod of a 

key).

27. Section 8.3.3: The discussion about de-registering compromised and noncompromised keys was modified.

28. Section 8.3.5: A discussion about how revocation is achieved for a PKI and for 

symmetric-key systems was added.

29. Appendix B.14.9 was revised to be consistent with SP 800-132.

30. The tags for references to FIPS were modified to remove the version number. The 

version number is provided in Appendix C.

In 2015, several editorial corrections and clarifications were made, and the following 

revisions were also made:

1. Changed the reference to SP 800-21 to SP 800-175.

2. Corrected web site links.

3. Section 1.4: Now refer to FIPS and NIST Recommendations as "NIST standards." 

Explain the concept of the cryptographic toolkit (in a footnote).

4. Section 2.1: Modified the definitions of Algorithm originator-usage period, 

Archive, authentication, authentication code, certification authority, DRBG, 

Digital signature, Key derivation, Key-encrypting key, Key Management Policy, 

Key transport, Key update, Key wrapping, Key-wrapping key, Message 

authentication code, Non-repudiation, Owner, Recipient-usage period, RBG seed, 

Secure communication protocol, Security services, Signature generation, 

Signature verification, Source authentication, and Trust anchor.

Added definitions for Data-encryption key, Identity authentication, Integrity 

authentication, Integrity protection, Key-derivation method, Key length, NIST 

standards, and Source authentication.

Removed the definitions of Key attribute and Work.

5. Section 2.2: Referenced the applicable publications.

6. Many of the mentions of "attributes" have been changed to "metadata" to align 

with discussions in SP 800-152.
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7. Section 3 and throughout the document: more clearly discusses authentication as 

either integrity authentication or source authentication. Identity authentication has 

been considered as source authentication.

8. Section 3.3: Rewritten to more clearly discuss integrity authentication or source 

authentication.

9. Section 3.4: Rewritten to more clearly discuss the how authorization is obtained.

10. Section 3.5: Rewritten to provide a more realistic discussion of non-repudiation, 

i.e., discussing support for non-repudiation, rather than actually providing nonrepudiation. References to non-repudiation in the document have been rewritten 

to discuss support for non-repudiation.

11. Section 3.7: The examples have been rewritten.

12. Inserted references to FIPS 202, as well as to FIPS 180.

13. Section 4.1: Remove a reference to the Dual_EC_DRBG specified in SP 800-

90A.

14. Section 4.2.2.2: Rewritten to address the non-approval of two-key TDEA for 

applying protection after 2015 (as indicated in SP 800-131A). 

15. Section 4.2.2.3: Inserted rationale for not using the ECB mode.

16. Section 4.2.3.1: Revised to refer to both the CMAC and GMAC modes of 

operation.

17. Section 4.2.4:Rewritten to provide more information about FIPS 186.

18. Section 4.2.5.1: Further discussion of SP 800-56A has been included.

19. Section 4.2.5.3: Added references to SP 800-56A and SP 800-56B for discussion 

of the security properties of the key-establishment schemes.

20. Section 4.2.5.4: Rewritten to clarify the use of "key wrapping"vs. "key 

encryption" in the document.

21. Section 4.2.7: Rewritten to describe SP 800-90A, SP 800-90B and SP 800-90C.

22. Section 5.1.1: More details added to the symmetric data-encryption key, 

symmetric key-wrapping key, and public key-transport key.

Added notes of intent to the private and public authentication keys.

23. Section 5.2: The use of "should" in the first line has been changed to "shall" to 

more strongly indicate that keys must not be used for multiple purposes. The use 

of "should" presented a conflict with later discussions in the document.

24. Section 5.3.1: Added a reference to quantum computers in the list.

25. Section 5.3.4: Rewritten to discuss the originator-usage period and recipient usage 

period of asymmetric key pairs.

26. Section 5.3.6: Further clarification of the cryptoperiod added to the Private 

signature key (footnote), Public signature verification key, Private authentication 

key (footnote), Public authentication key (footnote), Symmetric authentication 
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key, Symmetric key-agreement key, Symmetric key-wrapping key, Symmetric 

RBG keys, Public key-transport key, and Private static key-agreement key.

Corrected Symmetric data-encryption key and Symmetric key-wrapping key to 

agree with Table 1.

Table 1: Modified the header to refer to the originator-usage period and the 

recipient-usage period. Added a note to the Symmetric key-agreement key for 

clarification.

27. Section 5.4.2: Additional information inserted about obtaining assurance of 

domain parameter validity.

28. Section 5.4.3: Additional information inserted about obtaining assurance of public 

key validity.

29. Section 5.4.4: The details about obtaining assurance of private key possession 

have been removed, since this is discussed in SP 800-89. A note was added that 

this assurance could be obtained by a CA.

30. Section 5.5: Unnecessary text has been removed.

31. Section 5.6.1: The security-strength discussion has been revised, and a reference 

to SP 800-158 has been inserted. 

Deleted a note about the block size that was unnecessary.

Table 2 has been revised to provide a visual indication of which key sizes are no 

longer approved for applying cryptographic protection, which are approved, and 

which are approved, but not specifically mentioned in the FIPS standards. The 

note about SHA-1 was modified.

Table 3 and the following text have been revised to clearly indicate that SHA-1 is 

no longer approved for generating digital signatures. The SHA-3 hash functions 

are now included in the table. A note has been added to the header for HMAC.

32. Section 5.6.2: Table 4 has been updated to indicate the currently projected 

security strength time frames.

33. Section 5.6.3: A reference to SP 800-158 has been inserted for discussions about 

determining the actual security strength of a key, based on how it was generated 

and subsequently handled.

34. Section 6.1: Changes have been made to the integrity and confidentiality 

protection topics to be consistent with [SP 800-152]. For the integrity protection 

topic, " integrity protection can be provided by cryptographic integrity 

mechanisms..." has been changed to " integrity protection shall be provided by 

cryptographic integrity mechanisms...".

35. Section 6.2: An "in use" state has been introduced, along with an 

acknowledgement that the key may also be in transit and/or in storage.

36. Section 6.2.1.3: additional guidance has been added about the generation of the 

key components.
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37. Section 6.2.2.1: A paragraph has been added to mention a case where the 

availability of a key is not desired, and providing a reference to a publication that 

discusses cryptographic sanitization.

38. Section 6.2.2.3: Addition text was inserted to address the [FIPS 140-2] security 

level in accordance with [SP 800-152].

39. Section 6.2.3.1: A key's history has been inserted as a possible metadata item. A 

reference to SP 800-158 has been included to provide guidance on handling 

metadata.

40. Section 7 has been completely rewritten, including adding a suspended state and 

providing clarity on the transitions of the different key types. A suspended state 

has been added to Figure 3 and the discussion.

41. Section 8: The suspended state has been added to the discussions and included in 

Figure 5.

42. Section 8.1.5: A reference to SP 800-133 has been included.

43. Section 8.1.5.1: A sentence has been added to the end of paragraph 2 about 

distributing keying material to an organization's sub-entities.

44. Section 8.1.5.1.1.1: The section has been revised to clearly and more correctly 

describe what a trust anchor is (i.e., a CA, not a certificate for that CA).

45. Section 8.1.5.1.2: A reference to SP 800-56B has been removed, since it does not 

include schemes that use ephemeral keys.

46. Section 8.1.5.2, 8.1.5.2.2, and 8.2.3.2: References to the use of key update as an 

approved method for key change have been removed or modified.

47. Section 8.1.5.2.2.2: References to SP 800-38F, SP 800-56A and SP 800-56B have 

been added. A note has been added to mention authenticated encryption modes.

48. Section 8.1.5.2.3: Mentions of key wrapping have been removed, since it is not 

used in key-agreement schemes.

49. Section 8.1.5.3.4 has been rewritten.

50. Sections 8.2.1.1 and 8.2.1.2 : The mention of a "device" has been removed, as the 

appropriate reference is to cryptographic modules.

51. Section 8.2.3.2: Key update is now disallowed, as stated in SP 800-152.

52. Section 8.3.1: More guidance has been provided on using archives.

53. Section 8.3.4: The text was modified to discuss the destruction of a key, rather 

than the destruction of the media containing a destroyed key.

54. Section 8.3.5, paragraph 6: "...the corresponding public-key certificate should be 

revoked " has been changed to "...the corresponding public-key certificate shall

be revoked as soon as possible," and more guidance has been provided about 

using revoked certificates.

55. Section 10: A reference has been included to SP 800-130 and SP 800-152.
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54. Section 10.2.7: A reference to identity-based privileging has been added.

55. Appendix B.3: The first list of decision items has been replaced with a reference 

to Section 8.2.2.2 to avoid duplication.

56. Appendix B.3.3.1: The first sentence has been rewritten verify the edentity of the 

entity...", rather than "verify the authenticity...".

57. Appendix B.3.3.2: Rewritten.

58. Appendix B.3.4 and B.3.5: Text about the security strength has been removed as 

being inappropriate for this section.

59. Appendix C: The references have been updated, including the addition of FIPS 

202, SP 800-38G, SP 800-90, SP 800-130 and SP 800-152.