Archived NIST Technical Series Publication
The attached publication has been archived (withdrawn), and is provided solely for historical purposes.
It may have been superseded by another publication (indicated below).

Archived Publication
Series/Number:
Title:NIST Special Publication 800-131A
Transitions: Recommendation for Transitioning the Use of Cryptographic
Algorithms and Key Lengths

Publication Date(s):January 2011

Withdrawal Date:

November 2015

Withdrawal Note:

SP 800-131A is superseded in its entirety by the publication of
SP 800-131SAr1 (November 2015).

Superseding Publication(s)The attached publication has been superseded by the following publication(s):Series/Number:
Title:
Author(s):NIST Special Publication 800-131A Rev. 1
Transitions: Recommendation for Transitioning the Use of Cryptographic
Algorithms and Key Lengths

Elaine Barker, Allen Roginsky

Publication Date(s):November 2015

URL/DOI:

http://dx.doi.org/10.6028/NIST.SP.800-131Ar1

Additional Information (if applicable)
Contact:
Latest revision of theComputer Security Division (Information Technology Lab)

SP 800-131Ar1 (as of April 13, 2016)attached publication:
Related information:
Withdrawal
announcement (link):

http://csrc.nist.gov/groups/SNS/piv/
N/A

Date updated: Ɖƌŝůϭϯ, 201ϲ

NIST Special Publication 800-131A

Transitions: Recommendation forTransitioning the Use of Cryptographic
Algorithms and Key Lengths
Elaine Barker and Allen Roginsky
Computer Security Division
Information Technology Laboratory

COMPUTER SECURITY
January 2011

U.S. Department of Commerce
Gary Locke, Secretary

National Institute of Standards and Technology
Patrick Gallagher, Director

SP 800-131A

January 2011

Abstract
At the start of the 21st century, the National Institute of Standards and Technology(NIST) began the task of providing cryptographic key management guidance, which
includes defining and implementing appropriate key management procedures, using
algorithms that adequately protect sensitive information, and planning ahead for possible
changes in the use of cryptography because of algorithm breaks or the availability ofmore powerful computing techniques. NIST Special Publication (SP) 800-57, Part 1 was
the first document produced in this effort, and includes a general approach fortransitioning from one algorithm or key length to another. This Recommendation (SP800-131A) provides more specific guidance for transitions to the use of stronger
cryptographic keys and more robust algorithms.

Key Words: cryptographic algorithm, digital signatures, encryption, hash function, key
agreement, key derivation, key management, key transport, key wrapping, message
authentication codes, random number generation, security strength, transition.

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January 2011

Authority
This publication has been developed by the National Institute of Standards andTechnology (NIST) in furtherance of its statutory responsibilities under the Federal
Information Security Management Act (FISMA) of 2002, Public Law 107-347.
NIST is responsible for developing standards and guidelines, including minimum
requirements, for providing adequate information security for all agency operations andassets, but such standards and guidelines shall not apply to national security systems.
This Recommendation has been prepared for use by federal agencies. It may be used by
non-governmental organizations on a voluntary basis and is not subject to copyright.
(Attribution would be appreciated by NIST.)
Nothing in this document should be taken to contradict standards and guidelines mademandatory and binding on federal agencies by the Secretary of Commerce under statutory
authority. Nor should these guidelines be interpreted as altering or superseding theexisting authorities of the Secretary of Commerce, Director of the OMB, or any otherfederal official.
Conformance testing for implementations of this Recommendation will be conductedwithin the framework of the Cryptographic Module Validation Program (CMVP) and the
Cryptographic Algorithm Validation Program). The requirements of thisRecommendation are indicated by the word “shall.” Some of these requirements may beout-of-scope for CMVP or CAVP validation testing, and thus are the responsibility ofentities using, implementing, installing or configuring applications that incorporate thisRecommendation.

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January 2011

Table of Contents
1 Introduction............................................................................................................... 1
1.1 Background and Purpose ................................................................................................. 1
1.2 Useful Terms for Understanding this Recommendation ................................................. 1
1.2.1 Security Strengths ................................................................................................ 1
1.2.2 Definition of Terms.............................................................................................. 2
2 Encryption ................................................................................................................. 3
3 Digital Signatures ..................................................................................................... 4
4 Random Number Generation................................................................................... 6
5 Key Agreement Using Diffie-Hellman and MQV..................................................... 7
6 Key Agreement and Key Transport Using RSA ................................................... 10
7 Key Wrapping.......................................................................................................... 11
8 Deriving Additional Keys from a Cryptographic Key .......................................... 12
9 Hash Functions....................................................................................................... 13
10 Message Authentication Codes (MACs)............................................................... 14
Appendix A: Decision Rationale................................................................................. 17
A.1 Security Strength of the Two-Key Triple DES Encryption Algorithm ......................... 17
A.2 Rationale for Extending the Deadline for a Transition to Digital Signature Keys
Providing 112 Bits of Security Strength ........................................................................ 17
Appendix B: Mitigating Risk When Using Algorithms and Keys for LegacyUse ........................................................................................................................... 19
B.1 Decryption and Key Unwrapping Using Symmetric Key Algorithms (e.g., Twokey Triple DES) ............................................................................................................. 19
B.2 Digital Signature Generation Using Asymmetric (Public) Keys and SHA-1................ 20
B.3 Digital Signature Verification Using Asymmetric (Public) Keys and SHA-1 .............. 20
B.4 Verification of Message Authentication Codes (MACs) Using CMAC ....................... 21
Appendix C: References.............................................................................................. 22

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Transitions: Recommendation for Transitioning the Use of
Cryptographic Algorithms and Key Lengths1

Introduction

1.1
Background and Purpose
At the beginning of the 21st century, the National Institute of Standards and Technology(NIST) began the task of providing cryptographic key management guidance. This
included lessons learned over many years of dealing with key management issues, and isintended to encourage the definition and implementation of appropriate key management
procedures, to use algorithms that adequately protect sensitive information, and to planahead for possible changes in the use of cryptography because of algorithm breaks or theavailability of more powerful computing techniques. General key management guidance,
including the general approach for transitioning from one algorithm or key length toanother, is addressed in Part 1 of Special Publication (SP) 800-57 [SP 800-57].
This Recommendation (SP 800-131A) is intended to provide more detail about thetransitions associated with the use of cryptography by Federal government agencies forthe protection of sensitive, but unclassified information. The Recommendation addresses
the use of algorithms and key lengths; the validation of cryptographic modules that utilize
them is provided in [SP 800-131B].
The dates provided in SP 800-131A may differ from the dates originally provided in the2005 version of [SP 800-57]. The revised dates provided herein attempt to deal with therealities associated with an orderly transition and are based on a better understanding of
the risks associated with extending the dates in those cases where this was done. Notethat an upper-date limit is not provided herein for many of the algorithms and key lengths
discussed; that information is provided in [SP 800-57], and should be considered valid
unless different guidance is provided in the future.
1.2

Useful Terms for Understanding this Recommendation

1.2.1

Security Strengths

Some of the guidance provided in [SP 800-57] includes the definition of security
strengths, the association of the approved algorithms and key lengths with these security
strengths, and a projection of the time frames during which the algorithms and key
lengths could be expected to provide adequate security. Note that the length of thecryptographic keys is an integral part of these determinations.

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January 2011

The security strength of an algorithm with a particular key length1 is measured in bits andis, basically, a measure of the difficulty of discovering the key. The understood security
strength for each algorithm is provided in [SP 800-57].
The appropriate security strength to be used depends on the sensitivity of the data being
protected, and needs to be determined by the owner of that data (e.g., a person or an
organization). For the Federal government, a minimum security strength of 80 bits is
recommended in 2010; a minimum security strength of 112 bits is strongly
recommended, beginning in 2011 (see [SP 800-57]). However, with the acceptance of acertain amount of risk, the minimum of 80 bits of security strength may be used until theend of 2013. Based on the latest understanding of the state of the art for breaking thecryptographic algorithms, given particular key lengths, the transition to the 112-bit
security strength shall be accomplished by 2014, except where specifically indicated. See
Appendix A for an explanation.
Specific key lengths are provided in [FIPS 186-3] for DSA, ECDSA and RSA digital
signatures, in [SP 800-56A] for Diffie Hellman and MQV key agreement, and in [SP
800-56B] for RSA key agreement and key transport. These key lengths are strongly
recommended for interoperability, and their security strengths are provided in [SP 80057]. However, other key lengths are commonly used. The security strengths associatedwith these key lengths may be determined using the formula provided in the [FIPS 140-2]
Implementation Guideline [IG 7.5]. In this Recommendation (SP 800-131A), security
strengths of 80 bits and 112 bits are specifically addressed. The reference to 80 bits of
security strength should be interpreted as a security strength of at least 80 bits, but lessthan 112 bits (i.e., 80  security strength < 112).
1.2.2

Definition of Terms

The terms “approved”, “acceptable”, “deprecated”, “restricted” and “legacy-use” areused throughout this Recommendation.

1•

Approved is used to mean that an algorithm is specified in a FIPS or NIST
Recommendation (published as a NIST Special Publication).

•

Acceptable is used to mean that the algorithm and key length is safe to use; nosecurity risk is currently known.

•

Deprecated means that the use of the algorithm and key length is allowed, but theuser must accept some risk. The term is used when discussing the key lengths or
algorithms that may be used to apply cryptographic protection to data (e.g.,encrypting or generating a digital signature).

•

Restricted means that the use of the algorithm or key length is deprecated, andthere are additional restrictions required to use the algorithm or key length for
applying cryptographic protection to data (e.g., encrypting).

•

Legacy-use means that the algorithm or key length may be used to process
already protected information (e.g., to decrypt ciphertext data or to verify a digital

The term “key size” is commonly used in other documents.

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SP 800-131A

January 2011

signature), but there may be risk in doing so. Methods for mitigating this risk
should be considered (see Appendix B).
The use of algorithms and key lengths for which the terms deprecated, restricted andlegacy-use are listed require that the user must accept some risk that increases over time.
If a user determines that the risk is unacceptable, then the algorithm or key length isconsidered disallowed, from the perspective of that user. It is the responsibility of theuser or the user’s organization to determine the level of risk that can be tolerated for an
application and its associated data and to define any methods for mitigating those risks.
Other cryptographic terms used in this Recommendation are defined in the documents
listed in Appendix C.

2

Encryption

Encryption is a cryptographic operation that is used to provide confidentiality forsensitive information; decryption is the inverse operation. Several algorithms are
currently approved for encryption by the Federal government:•

Triple DES is specified in [SP 800-67], and has two key lengths, known as twokey Triple DES and three-key Triple DES. Two-key Triple DES has beenassessed at a security strength of 80 bits2, whereas three-key Triple DES is
assessed at a security strength of 112 bits.

•

SKIPJACK was approved in [FIPS 185], and is assessed at a security strengthof 80 bits.

•

AES is specified in [FIPS 197]. It has three approved key lengths: 128, 192 and256 bits. AES-128 is assessed at a security strength of 128 bits, AES 192 at asecurity strength of 192 bits, and AES-256 at a security strength of 256 bits.

The transition schedule for encryption algorithms is provided in Table 1.
Table 1: Encryption Transitions
Algorithm

Use

Two-key Triple DES Encryption

Acceptable through 2010
Restricted use from 2011 through2015
Disallowed after 2015

Two-key Triple DES Decryption

Acceptable through 2010
Legacy-use after 2010

Three-key Triple DES Encryption and Decryption
SKIPJACK Encryption

Acceptable
Acceptable through 20102

The assessment of at least 80-bits of security for two-key Triple DES is based on the assumption that an
attacker has approximately 240 matched plaintext and ciphertext blocks.

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January 2011
Acceptable through 2010
Legacy-use after 2010

SKIPJACK Decryption
AES-128 Encryption and Decryption

Acceptable

AES-192 Encryption and Decryption

Acceptable

AES-256 Encryption and Decryption

Acceptable

Two-key Triple DES encryption:
The use of two-key Triple DES is acceptable for encryption through December 31,
2010.
From January 1, 2011 through December 31, 2015, the use of two-key Triple DES forencryption is restricted: the total number of blocks of data encrypted with the same
cryptographic key shall not be greater than 220 (note that for this algorithm, a block is
the 64-bit block of a Triple DES encryption operation). This restriction also applies tothose keys that were first used prior to 2011 and continue to be used beyond
December 31, 2010 (i.e., those keys whose cryptoperiod begins prior to 2011 andextends into 2011). Rationale for this exception is provided in Appendix A.1.
After December 31, 2015, two-key Triple DES shall not be used for encryption.
Two-key Triple DES decryption:
Decryption using two-key Triple DES is acceptable through 2010.
Decryption using two-key Triple DES is allowed for legacy-use after 2010
SKIPJACK encryption and decryption:
The use of SKIPJACK for encryption is acceptable through December 31, 2010.
SKIPJACK shall not be used for encryption thereafter.
The use of SKIPJACK for decryption is acceptable through 2010.
The use of SKIPJACK for decryption is allowed for legacy-use after 2010
AES and three-key Triple DES encryption and decryption:
The use of AES-128, AES-192, AES-256 and three-key Triple DES is acceptable.

3

Digital Signatures

Digital signatures are used to provide assurance of origin authentication and data
integrity. These assurances are sometimes extended to provide assurance that a party in a
dispute (the signatory) cannot repudiate (i.e., refute) the validity of the signed document;
this is commonly known as non-repudiation. The digital signature algorithms approvedin [FIPS 186-2] and [FIPS 186-3] are DSA, ECDSA and RSA.
The generation of a digital signature on data requires the use of 1) a cryptographic hashfunction that operates on the data to be signed, and 2) the use of a cryptographic key anda signing algorithm to generate a signature on the output of the hash function (and, byextension, the data that is intended to be signed). This section addresses the use of the4

SP 800-131A

January 2011

cryptographic keys used with the signing algorithm; discussions of the hash function to
be used during the generation of digital signatures are provided in Section 9. The detailsof the security strengths of the algorithms and the key lengths used can be found in [SP
800-57].
Note that the security strength of digital signatures is determined by the security strengthof both the cryptographic key with the signing algorithm, and the cryptographic hashfunction used.
Table 2 provides the schedule for transitioning from digital signatures providing at least
80 bits of security strength to those providing at least 112 bits of security strength.

Table 2: Digital Signatures Security Strength Transitions
Digital Signature
ProcessUse
80 bits of security strength:
DSA: ((|p|  1024) and (|q|  160))
and((|p| < 2048) OR (|q| < 224))
RSA: 1024  |n| < 2048

Digital Signature
Generation

Acceptable through2010
Deprecated from 2011
through 2013
Disallowed after 2013

EC: 160  |n| < 224 112 bits of security strength:
DSA: |p|  2048 and|q|  224
Acceptable
RSA: |n|  2048
EC: |n|  224

Digital Signature
Verification

80 bits of security strength:
DSA: ((|p|  1024) and (|q|  160))
and((|p| < 2048) OR (|q| < 224))
RSA: 1024  |n| < 2048
EC: 160  |n| < 224

5

Acceptable through2010
Legacy-use after 2010

SP 800-131A

January 2011
 112 bits of security strength:
DSA: |p|  2048 and|q|  224
Acceptable
RSA: |n|  2048
EC: |n|  224

Digital signature generation:
The use of key lengths providing 80 bits of security strength is acceptable for digital
signature generation through December 31, 2010.
From January 1, 2011 through December 31, 2013, the use of key lengths providing
80 bits of security strength is deprecated. The user must accept risk when using thesekeys, particularly when approaching the December 31, 2013 upper-limit date. This isespecially critical for digital signatures on data whose signature is required to be valid
beyond this date. Appendix A.2 provides rationale for this modified guidance. See
Section 5.6.2 of [SP 800-57] for further guidance.
After December 31, 2013, key lengths providing less than 112 bits of security
strength shall not be used to generate digital signatures.
Key lengths providing at least 112 bits of security are acceptable.
Digital signature verification:
Key lengths providing 80 bits of security using approved digital signature algorithms
are acceptable through 2010.
Key lengths providing 80 bits of security using approved digital signature algorithms
are allowed for legacy-use after 2010.
Key lengths providing at least 112 bits of security using approved digital signaturealgorithms are acceptable.

4

Random Number Generation

Random numbers are used for various purposes, such as the generation of keys, nonces
and authentication challenges. Several random number generators (RNGs) have been
approved for use by the Federal government. Until relatively recently, [FIPS 186-2] wasthe approval vehicle for RNGs, specifying RNGs and approving the RNGs in American
National Standard (ANS) X9.31-1998 [X9.31] and ANS X9.62-1998 [X9.62].
In 2007, a new set of RNGs were approved in SP 800-90 [SP 800-90] that provide
higher levels of security than the previously-approved RNGs. In addition, [SP 800-90]
contains more comprehensive guidance on RNG use. Note that in [SP 800-90], the term
“random bit generator” (RBG) is used instead of “random number generator” (RNG); any

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January 2011

difference is not important for this Recommendation (i.e., SP 800-131A), but both terms
will be used below.
Note that in 2005, a revision of [X9.62] was approved that includes the HMAC_DRBG
specified in [SP 800-90], and does not include the RNGs in the 1998 version.
The transition schedule for RBGs and RNGs is provided in Table 3.
RBGs that are compliant with SP 800-90 are acceptable.
The use of the RNGs specified in FIPS 186-2, [X9.31] and [X9.62] is acceptable throughDecember 31, 2010.
The use of the RNGs specified in FIPS 186-2, [X9.31] and ANS [X9.62] is deprecatedfrom 2011 through December 31, 2015, and disallowed after 2015.
Table 3: Random Number Generation Transitions
Description
RBGs specified in SP 800-90 (HASH, HMAC,
CTR, DUAL_EC) and ANS X9.62-2005(HMAC)
RNGs specified in FIPS 186-2, ANS X9.31-1998
and ANS X9.62-1998

5

Use
Acceptable
Acceptable through 2010
Deprecated from 2011 through 2015
Disallowed after 2015

Key Agreement Using Diffie-Hellman and MQV

Key agreement is a technique that is used to establish symmetric keys between two
entities that intend to communicate, whereby both parties contribute information to the
key agreement process. Two families of key agreement schemes are defined and havebeen approved in [SP 800-56A]: Diffie-Hellman (DH) and MQV. Each has been definedover two different mathematical structures: finite fields and elliptic curves. Key
agreement includes two steps: the use of an appropriate DH or MQV “primitive” togenerate a shared secret, and the use of a key derivation function (KDF) to generate one
or more keys from the shared secret. [SP 800-56A] contains approved DH and MQVprimitives and approved KDFs for key agreement.
Several protocol standards specify one or more of the DH or MQV primitives specified in[SP 800-56A], but use different KDFs; the specifically-approved key agreement schemes
to be used by these protocols are provided in [SP 800-135].
Other key agreement schemes that are not specified in either SP 800-56A or SP 800-135
are allowed by the FIPS 140-2 Implementation Guideline [IG D.2]; these will be
discussed below as the non-compliant schemes.
Table 4 contains the transition schedule for DH and MQV key agreement schemes.
Table 4: SP 800-56A Key Agreement (DH and MQV)
Usea

Scheme7

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January 2011

SchemeSP 800-56A and SP 800-135
DH and MQV schemes using
finite fields

SP 800-56A and SP 800-135
DH and MQV schemes using
elliptic curves

Non-compliant DH and
MQV schemes using finite
fields|p| = 1024 bits, and|q| = 160 bits

Usea
Acceptable through 2010
Deprecated from 2011 through2013
Disallowed after 2013

|p| = 2048 bits, and|q| = 224 or 256 bits

Acceptable

160  |n|  223 bitsand|h|  10

Acceptable through 2010
Deprecated from 2011 through2013
Disallowed after 2013|n|  224 bits and has specified in Table
5

Acceptable|p|  1024 bits, and|q|  160 bits|p|  2048 bits, and|q|  224 bits|n|  160
Non-compliant DH and
MQV schemes using elliptic
curves

Acceptable through 2010
Deprecated from 2011 through2013

Deprecated after 2013. All othervalues of p and q are disallowed
after 2013
Acceptable through 2010
Deprecated from 2011 through2013

Deprecated after 2013. All othervalues of n are disallowed after2013|p|, |q|, |n| and |h| are used to denote the bit length of p, q, n and h, respectively.
|n|  224a

SP 800-56A and SP 800-135 DH and MQV schemes using finite fields:
Through December 31, 2010, the use of |p| = 1024 bits, and |q| = 160 bits is
acceptable, where p is the field order (i.e., the modulus), and q is the subgroup order.
Note that the length of p is also the length of the public key, and the length of q is thelength of the private key. In [SP 800-56A], these parameters are denoted as parameter
set FA.
From January 1, 2011 through December 31, 2013, the use of |p| = 1024 bits, and |q|= 160 bits is deprecated. The rationale for extending the transition is similar to thatfor digital signatures, which is discussed in Appendix A.2.

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January 2011

After December 31, 2013, |p| = 1024 bits, and |q| = 160 bits shall not be used in a
key agreement scheme.
The use of |p| = 2048 bits, and |q| = 224 or 256 bits is acceptable. In [SP 800-56A],|p| = 2048 bits, and |q| = 224 are denoted as parameter set FB; and |p| = 2048 bits, and|q| = 256 are denoted as parameter set FC.
SP 800-56A and SP 800-135 DH and MQV schemes using elliptic curves:
Through December 31, 2010, the use of 160  |n|  223 bits and |h|  10 is
acceptable, where n is the number of elements in the subgroup, and h is the cofactorof n for the order of the elliptic curve.
From January 1, 2011 through December 31, 2013, the use of 160  |n|  223 bits and|h|  10 is deprecated. The rationale for extending the transition is similar to that for
digital signatures, which is discussed in Appendix A.2.
After December 31, 2013, |n|  223 bits shall not be used in a key agreement scheme.
The use of |n|  224 bits and h as specified in Table 5 is acceptable. In [SP 800-56A],
four parameter sets are defined: EB – EE. The acceptable values for n and h areprovided in [SP 800-56A] and in the following table.
Table 5: EC Parameter sets
EB

EC

ED

EE

Length of n224-255

256-383384-511512+

Maximum bit
length ofcofactor h

14

16

24

32

Non-compliant DH and MQV schemes using finite fields:
Through December 31, 2010, the use of |p|  1024 bits, and |q|  160 bits is
acceptable.
From January 1, 2011 through December 31, 2013, the use of |p|  1024 bits, and |q| 160 bits is deprecated. The rationale for extending the transition is similar to thatfor digital signatures, which is discussed in Appendix A.2.
After December 31, 2013, the use of |p|  2048 and |q|  224 is deprecated. Values ofp or q that do not meet this condition shall not be used.
Non-compliant DH and MQV schemes using elliptic curves:
Through December 31, 2010, the use of |n|  160 bits is acceptable.
From January 1, 2011 through December 31, 2013, the use of |n|  160 bits isdeprecated. The rationale for extending the transition is similar to that for digital
signatures, which is discussed in Appendix A.2.
After December 31, 2013, the use of |n|  224 is deprecated. Values of |n| < 224
shall not be used.

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6

January 2011

Key Agreement and Key Transport Using RSA[SP 800-56B] specifies the use of RSA for both key agreement and key transport. Key
agreement is a technique in which both parties contribute information to the key
agreement process. Key transport is a key establishment technique in which only one
party determines the key. Some protocols that include key transport schemes are provided
in [IG D.2]; these will be discussed below as the non-56B-compliant schemes. Note thatin [IG D.2], key transport is often referred to as key wrapping. Note also that while there
are implementations of RSA-based Key Transport schemes that are not compliant with
SP 800-56B, there are no RSA-based Key Agreement schemes that are not compliant
with SP 800-56B.
Guidance on approved key lengths for RSA is provided in [SP 800-56B]. Table 6
provides the transition schedule.
In the case of key transport keys (i.e., the keys used to encrypt other keys for transport),
this Recommendation (SP 800-131A) applies to both the encryption and decryption of thetransported keys.
Table 6: RSA-based Key Agreement and Key Transport Key Length Transitions
SchemeUse
Acceptable through 2010|n| = 1024 bits
Deprecated from 2011 through 2013
SP 800-56B Key
Disallowed after 2013
Agreement schemes|n| = 2048 bits

Acceptable
Acceptable through 2010

SP 800-56B Key
Transport schemesNon-56B-compliant
Key Transport schemes|n| = 1024 bits

Deprecated from 2011 through 2013
Disallowed after 2013|n| = 2048 bits

Acceptable|n|  1024 bits

Acceptable through 2010
Deprecated from 2011 through 2013|n|  2048 bits

Deprecated after 2013. All other valuesof n < 2048 bits are disallowed after2013

SP 800-56B RSA Key Agreement schemes:
The use of RSA key agreement schemes with |n| = 1024 is acceptable throughDecember 31, 2010.

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From January 1, 2011 through December 31, 2013, the use of RSA key agreement
schemes with |n| = 1024 is deprecated. The rationale for extending the transition issimilar to that for digital signatures, which is discussed in Appendix A.2.
After December 31, 2013, RSA key agreement schemes with |n| = 1024 shall not beused.
The use of RSA key agreement schemes with |n| = 2048 is acceptable.
SP 800-56B RSA Key Transport schemes:
The use of RSA key transport schemes with |n| = 1024 is acceptable throughDecember 31, 2010.
From January 1, 2011 through December 31, 2013, the use of RSA key transport
schemes with |n| = 1024 is deprecated. The rationale for extending the transition issimilar to that for digital signatures, which is discussed in Appendix A.2.
After December 31, 2013, RSA key transport schemes with |n| = 1024 shall not beused.
The use of RSA key transport schemes with |n| = 2048 is acceptable.
Non-56B-compliant RSA Key Transport schemes:
The use of RSA key transport schemes with |n|  1024 is acceptable throughDecember 31, 2010.
From January 1, 2011 through December 31, 2013, the use of RSA key transport
schemes with |n|  1024 is deprecated. The rationale for extending the transition issimilar to that for digital signatures, which is discussed in Appendix A.2.
After December 31, 2013, the use of |n|  2048 is deprecated. Values of |n|< 2048
shall not be used.

7

Key Wrapping

Key wrapping is the encryption of a symmetric key by another symmetric key withintegrity protection. Symmetric keys are used with algorithms such as Triple-DES and
AES. See [SP 800-57] for further information. As of 2010, neither a FIPS nor a NIST
Recommendation specify key wrapping algorithms, although an informal specification
for key wrapping using AES is available at
http://csrc.nist.gov/groups/ST/toolkit/documents/kms/AES_key_wrap.pdf. However, [IGD.2] addresses key wrapping as defined in the AES key wrapping specification.
Table 7 provides the transition schedule.
Table 7: Symmetric Key Wrapping Key Length Transitions
Algorithm
Use
Acceptable through 2010
Restricted use from 2011 throughTwo-key Triple DES Key Wrap
2015
Disallowed after 201511

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January 2011
Acceptable through 2010
Legacy-use after 2010

Two-key Triple DES Key Unwrap

AES and Three-key Triple DES Key Wrap and Unwrap

Acceptable

Two-key Triple DES key wrapping:Two-key Triple DES is acceptable for wrapping and unwrapping keying material
through December 31, 2010.
From January 1, 2011 through December 31, 2015, the use of two-key Triple DES for
wrapping keying material is restricted: the total number of blocks of keying material
wrapped with the same cryptographic key shall be no more than 220.
After December 31, 2015, two-key Triple DES shall not be used to wrap keying
material.
Two-key Triple DES key unwrapping:
The use of two-key Triple DES is acceptable through December 31, 2010.
The use of two-key Triple DES is allowed for legacy-use after December 31, 2010.
AES and three-key Triple DES key wrapping and unwrapping:
AES and three-key Triple DES are acceptable for wrapping and unwrapping keying
material.

8

Deriving Additional Keys from a Cryptographic Key[SP 800-108] specifies key derivation functions that use a cryptographic key (called a key
derivation key) to generate additional keys. The key derivation key could be:• Generated using an approved RNG (see [IG 7.8] and [SP 800-133]),• Obtained using a key agreement or key transport scheme (see Sections 5 and 6 ofthis Recommendation, i.e., SP 800-131A), or• Obtained using a key wrapping algorithm (see Section 7).
Table 8 provides the transition of key lengths for key derivation.
Table 8: Key Length Transitions for a Key Derivation Function (KDF)
Algorithm
HMAC-based KDF

UseAcceptable

Two-key TDES-based KDF

Acceptable through 2010
Deprecated from 2011 through2015
Disallowed after 2015

AES- and Three-key Triple

Acceptable

CMAC-based KDF

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DES-based KDFs

HMAC-based KDF:
The use of HMAC-based KDFs is acceptable using an approved hash function,
including SHA-1. See Section 10 for discussions of the key lengths used with
HMAC.
CMAC-based KDF:
The use of two-key TDES as the block cipher algorithm in a CMAC-based KDF is
acceptable through December 31, 2010.
The use of two-key TDES as the block cipher algorithm in a CMAC-based KDF isdeprecated from 2011 through December 31, 2015.
Two-key Triple DES shall not be used to derive keying material after December 31,
2015.
The use of AES and three-key Triple DES as the block cipher algorithm in a CMACbased KDF is acceptable.

9

Hash Functions

Five approved hash functions are specified in [FIPS 180-3]. The security strengths forhash functions are dependent on their use, and are provided in [SP 800-57]. Additional
discussions about the different uses of hash functions are provided below and in [SP 800107].
Note that, while there have been attacks reported on SHA-1, this Recommendation (i.e.,
SP 800-131A) will consider its strength to be 80 bits for digital signature generation forthe purpose of discussion.
The transition schedule for hash functions is provided in Table 9.
Table 9: Hash Function Transitions
Hash Function

Use
Acceptable through 2010
Digital signature generation

Deprecated from 2011 through2013
Disallowed after 2013

SHA-1
Digital signature verification
Non-digital signature
generation applications
SHA-224

13

Acceptable through 2010
Legacy-use after 2010
AcceptableSP 800-131A
SHA-256January 2011
Acceptable for all hash function applications

SHA-384
SHA-512
SHA-1 for digital signature generation:
SHA-1 is acceptable for digital signature generation through December 31, 2010.
From January 1, 2011 through December 31, 2013, the use of SHA-1 is deprecatedfor digital signature generation. The user must accept risk when SHA-1 is used,particularly when approaching the December 31, 2013 upper limit. This is especiallycritical for digital signatures on data for which the signature is required to be valid
beyond this date. See Section 5.6.2 of [SP 800-57] for further guidance.
SHA-1 shall not be used for digital signature generation after December 31, 2013.
SHA-1 for digital signature verification:
For digital signature verification, the use of SHA-1 is acceptable through December
31, 2010.
For digital signature verification, SHA-1 is allowed for legacy-use after December
31, 2010.
SHA-1 for non-digital signature applications:
For all other hash function applications, the use of SHA-1 is acceptable. The otherapplications include HMAC, Key Derivation Functions (KDFs), Random Number
Generation (RNGs and RBGs), and hash-only applications (e.g., hashing passwords
and using SHA-1 to compute a checksum, such as the approved integrity techniquespecified in Section 4.6.1 of [FIPS 140-2]).
SHA-224, SHA-256, SHA-384, SHA-512:
The use of these hash functions is acceptable for all hash function applications.

10

Message Authentication Codes (MACs)

Two types of message authentication code mechanisms using symmetric keys have been
approved for use: those based on hash functions, and those based on block-cipher
algorithms. [FIPS 198-1] specifies a keyed-hash message authentication code (HMAC)
that uses a hash function; [SP 800-107] provides additional guidance on the uses of
HMAC. Block cipher modes for generating MACs are specified in [SP 800-38B], [SP
800-38C] and [SP 800-38D]. The CMAC mode specified in [SP 800-38B] uses either
AES or Triple DES; the CCM and GCM/GMAC modes specified in [SP 800-38C] and[SP 800-38D], respectively, use AES.
Table 10: Message Authentication Code Transitions
MAC Algorithm
HMAC Generation

Use
Key lengths  80 bits and< 112 bits
14

Acceptable through 2010
Deprecated from 2011 throughSP 800-131A

January 20112013
Disallowed after 2013
Key lengths  112 bits

Acceptable

Key lengths  80 bits and< 112 bits

Acceptable through 2010
Legacy-use after 2010

Key lengths  112 bits

Acceptable

Two-key Triple DES

Acceptable through 2010
Deprecated from 2011 through2015
Disallowed after 2015

AES and Three-key Triple
DES

Acceptable

Two-key Triple DES

Acceptable through 2010
Legacy-use after 2010

AES and Three-key Triple
DES

Acceptable

CCM and
GCM/GMAC
Generation

AES

Acceptable

CCM and
GCM/GMAC
Verification

AES

Acceptable

HMAC Verification

CMAC Generation

CMAC Verification

HMAC Generation:
Any approved hash function may be used.
The use of key lengths  80 bits, but < 112 bits is acceptable through December 31,
2010.
From January 1, 2011 through December 31, 2013, the use of key lengths  80 bits,
but < 112 bits is deprecated.
After December 31, 2013, key lengths < 112 bits shall not be used.
The use of key lengths  112 bits is acceptable.
HMAC Verification:
The use of key lengths  80 bits, but < 112 bits is acceptable through December 31,
2010.
The use of key lengths  80 bits, but < 112 bits is allowed for legacy-use after
December 31, 2010.

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The use of key lengths  112 bits is acceptable.
CMAC Generation:
The use of two-key Triple DES is acceptable through December 31, 2010.
From January 1, 2011 through December 31, 2015, the use of two-key Triple DES isdeprecated.
After December 31, 2015, two-key Triple DES shall not be used.
The use of AES and three-key Triple DES is acceptable.
CMAC Verification:
The use of two-key Triple DES is acceptable through December 31, 2010.
The use of two-key Triple DES is allowed for legacy-use after December 31, 2010.
The use of AES and three-key Triple DES is acceptable.
CCM and GCM/GMAC Generation and Verification:
The use of CCM and GCM/GMAC is acceptable.

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Appendix A: Decision Rationale
A.1

Security Strength of the Two-Key Triple DES Encryption Algorithm

The security strength of two-key Triple DES is discussed in Section 5.6.1 of [SP 800-57].
The estimate given there is 80 bits of security, assuming that the attacker has access toapproximately 240 (plaintext, ciphertext) pairs, where the plaintext is encrypted with thesame secret key that the attacker is trying to discover. The more general formula given in[OorWie91] says that the security strength of two-key Triple DES against the best known
attack is 120-n bits, where n is such that the attacker has access to 2n (plaintext,
ciphertext) pairs.
For the transition period from January 1, 2011 through December 31, 2015, the effective
100-bit security strength provided when no more than 220 blocks are encrypted with thesame key is allowed.
A.2

Rationale for Extending the Deadline for a Transition to Digital
Signature Keys Providing 112 Bits of Security StrengthWith the publication of SP 800-57, Part 1 in 2005, NIST announced the intent totransition from a minimum cryptographic security strength of 80 bits to a security
strength of 112 bits by the end of 2010.
The schedule was based on academic research available at that time indicating that thedigital signature algorithms using the 1024-bit RSA or DSA keys, would either be broken
or be in serious danger of being broken by this date. In addition, the expected increase in
the speed of computers and the anticipated improvement of the factoring techniques for
RSA justified this point of view.
However, in the five years since the proposal of the 2010 transition date, factoring
techniques have not progressed as quickly as anticipated. The first successful
factorization of a 768-bit RSA modulus was not reported until December 2009 (see[Factoring]). This effort required six months of computations using highly sophisticatedequipment. According to the paper’s authors, factoring a 1024-bit modulus would be“one thousand times harder” than a 768-bit one. This means that another 6-7 years arelikely to pass before 1024-bit numbers could realistically be factored.
In view of this research, and because some widely-used protocols still require the use of
the 1024-bit RSA keys, NIST decided to extend the transition date for keys of this length
for three years longer than originally anticipated, that is, through the end of 2013.
Similarly, the 1024-bit DSA keys and the 160-223 bit ECDSA keys can be used during
this time period. However, since such keys are more and more likely to be broken as the2013 date approaches, the data owner must understand and accept the risk of continuing
to use these keys to generate digital signatures. Hence, the use of such keys during the
2011-2013 transition period for the generation of digital signatures is marked as

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deprecated. As stated in Section 3, “After December 31, 2013, key lengths providing
less than 112 bits of security strength shall not be used to generate digital signatures.”
Signature verification will continue to be permissible with any key that provides at least
80 bits of security.

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Appendix B: Mitigating Risk When Using Algorithms and Keys
for Legacy-Use
Certain algorithms and key sizes are allowed for legacy-use when removing or verifying
the cryptographic protection already applied to sensitive information (e.g., decrypting
ciphertext or verifying a digital signature or message authentication code). However, auser must accept that the protection of the information may no longer be as good as
desired.
B.1

Decryption and Key Unwrapping Using Symmetric Key Algorithms(e.g., Two-key Triple DES)
Sensitive information may continue to need confidentiality protection beyond the datewhen the algorithm and key length used to protect that information are no longer
considered adequate.
Symmetric key algorithms use the same key for encryption to produce ciphertext data as
must be used to decrypt the ciphertext data back to the original plaintext data. However,since the algorithm and key length used to encrypt the information are no longer
considered secure, those entities using the algorithm to decrypt the ciphertext data should
consider that an adversary may be capable of determining the key that was used forencryption. If the adversary has access to the ciphertext data and can determine the key,then the data no longer has reliable confidentiality protection. That is, the owner of thesensitive information should consider the information to no longer be protected (i.e., theinformation should be considered as being in plaintext form).
Several scenarios need to be considered when evaluating whether or not the informationis or will remain secure.
1. If the ciphertext information was made available to an adversary (e.g., theciphertext was transmitted over the Internet), the ciphertext may have beenrecorded by the adversary. In such a case, there is a possibility that the adversary
can determine the key for decrypting the ciphertext, thus exposing the sensitive
information. The remaining items assume that this situation is not the case or thatthe probability is sufficiently low that other measures to further protect the
information are warranted.
2. If the ciphertext data is protected from exposure to potential attack (e.g., theciphertext data is saved in secure storage), then the confidentiality of theinformation as encrypted using the now-insecure algorithm or key length may
remain valid.
3. If the ciphertext data is re-encrypted or rewrapped3 using a stronger algorithm or
key length, then the confidentiality of the sensitive information will remain valid
as long as the stronger algorithm remains secure.
3

Decrypted or unwrapped using the original algorithm and key to produce the original plaintext, and thenencrypting or wrapping the plaintext using another algorithm and key.

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4. If the ciphertext data needs to be made publicly available (e.g., transmitted)
during the period in which the algorithm and key length are only allowed forlegacy-use, then the information must be re-encrypted or super-encrypted4 using amore secure algorithm and key length.
B.2

Digital Signature Generation Using Asymmetric (Public) Keys and
SHA-1
The purpose of a digital signature is to bind information to an entity. A party uses theirsecret (private) key to electronically sign a document. Everyone else can use this party’s
public key, which is not secret, to check that only the owner of the secret key could sign
the document.
Suppose, however, that the digital values of the signature were the same when twocompletely different messages were signed with the same private key. While the signing
entity signed one message only (this could be a purchase contract or any other financial
or legal document), the attacker could claim that a different message was signed. Thatother message would probably be more to the attacker’s liking and, presumably, thesigner would have never signed it. As the attacker does not know the signing party’s
private key, the only way for the attacker to force this collision of signatures is togenerate a hash function collision, since in the approved signature schemes, the signer
signs not the message itself, but the hash value of the message.
The SHA-1 hash function has at most 80 bits of security against collision attacks.
Therefore, it is quite likely that due to the advancement in computing technology and thediscovery of new attacks against the hash functions, the attackers will be able to generate,in the foreseeable future, the scenario described in the previous paragraph. Hence, it isimportant to find the mitigating factors that would not allow this to happen. NIST
recommends that during the 2011-2013 transition period, the users of the cryptographic
modules that perform digital signature generation carefully assess their risk and decide if
the risk of allowing SHA-1 in digital signature generation can be accepted. Someapplications, such as signing a public key certificate, are very high risk and the use of
SHA-1 in those applications should be avoided as much as possible. In NIST’s view,
after 2013, the risk is unacceptable in all applications, and the use of SHA-1 whengenerating a digital signature is not allowed after that date.
The verification of digital signatures generated prior to the end of 2013 may need to be
performed at a later date. Appendix B.3 addresses ways to mitigate the risk of validatinga signature that was generated using SHA-1.
B.3

Digital Signature Verification Using Asymmetric (Public) Keys and
SHA-1
Digital signatures are generated on information (e.g., a message) using a hash function,
an asymmetric private key and a signing algorithm. Such signatures are verified using theinformation that was signed (i.e., the message), the same hash function that was used
4

The ciphertext is encrypted or wrapped using an additional algorithm and key.

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during the generation of the digital signature, the public key associated with the private
key, the digital signature itself, and a verification algorithm. The digital signature on themessage may need to be verified and considered valid beyond the period when thesigning algorithm, hash function and private key are considered secure.
Asymmetric digital signature algorithms use different, but associated, keys for generating
and verifying the digital signatures. The only secret associated with these processes is theprivate key, which should only be known by the party that generates the signature; that is,
the hash function, the public key, the generating and verification algorithms, and themessage can be assumed to be known by an adversary. The adversary’s goal is to either
determine the private key using this known information, including other messages thatwere signed using the same private key, or to determine alternative information (i.e.,alternate messages) that produce the same digital signature. If the private key or othermessages can be so determined, the information that has already been signed is subject topossible attack (e.g., by substituting messages and signatures that are beneficial to theadversary). During the “legacy-use” period, the entity that is verifying the digital
signature should accept that an adversary may have at least one of these capabilities.
In order for the signed information to continue to be verifiable as valid, both the signed
information and the digital signature need to be protected against possible modification(e.g., placed in secure storage) or against modification without detection (e.g., timestamped and signed with an additional signature).
B.4 Verification of Message Authentication Codes (MACs) Using CMAC
A message authentication code (MAC) may need to remain verifiable and valid beyond
the date when the algorithm and key length used to generate the MAC are no longer
considered adequate.
As in the case of symmetric algorithms used for encryption (see Appendix B.1), the same
key is used to generate the MAC as must be used for verification of that MAC. Since thealgorithm and key length used to generate that MAC are no longer considered secure, an
entity that verifies a MAC using a no-longer-secure algorithm and key length should
assume that an adversary may be capable of determining the key that was used for MAC
generation. During the “legacy-use” period, the adversary may be assumed to be capableof determining the MAC key and generating MACs on new messages or substituting
more beneficial messages (beneficial to the adversary) that produce the same MAC.
In order for the MACed data to continue to be verifiable as valid during the “legacy-use”
period, both the MACed data and the MAC need to be protected against possible
modification or substitution (e.g., placed in secure storage).

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Appendix C: References
FIPS and SP documents are available at http://csrc.nist.gov/publications/, except for the
FIPS 140-2 Implementation Guidance, which is available at
http://csrc.nist.gov/groups/STM/cmvp/standards.html#02.
[FIPS 140-2]

Security Requirements for Cryptographic Modules, with Change
Notices, December 2002.

[FIPS 180-3]

Secure Hash Standard (SHS), October 2008.

[FIPS 185]

Escrowed Encryption Standard, Feb 1994.

[FIPS 186-2]

Digital Signature Standard, January 2000.

[FIPS 186-3]

Digital Signature Standard, June 2009.

[FIPS 197]

Advanced Encryption Standard, November 2001.

[FIPS 198-1]

Keyed-Hash Message Authentication Code (HMAC), July 2008.

[IG X.Y]

Implementation Guidance for FIPS 140-2 and the Cryptographic Module
Validation Program, where X.Y is the section number.

[SP 800-38B]

CMAC Mode of Authentication, May 2005.

[SP 800-38C]

Recommendation for Block Cipher Modes of Operation: the CCM Mode
for Authentication and Confidentiality, May 2004.

SP 800-38D]

Recommendation for Block Cipher Modes of Operation: Galois/Counter
Mode (GCM) and GMAC, November 2007.

[SP 800-56A]

Recommendation for Pair-Wise Key Establishment Schemes Using
Discrete Logarithm Cryptography, March 2007.

[SP 800-56B]

Recommendation for Pair-Wise Key Establishment Using Integer
Factorization, DRAFT, December 2008.

[SP 800-57]

Part 1, Recommendation for Key Management: General, March 2007.

[SP 800-67]

Recommendation for the Triple Data Encryption Algorithm (TDEA)
Block Cipher, May 2008.

[SP 800-90]

Recommendation for Random Number Generation Using Deterministic
Random Bit Generators, March 2007.

[SP 800-107]

Recommendation for Applications Using Approved Hash Algorithms,
February 2009.

[SP 800-108]

Recommendation for Key Derivation Using Pseudorandom Functions,November 2008.

[SP 800-131B] Transitions: Validation of Transitioning Cryptographic Algorithms and
Key Lengths, under development.

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[SP 800-133]

Recommendation for Cryptographic Key Generation, underdevelopment.

[SP 800-135]

Recommendation for Existing Application-Specific Key Derivation
Functions, Draft.

Non-NIST References:[Factoring]

T. Kleinjung et al, “Factorization of a 768-bit RSA Modulus), February
18, 2010.

[OorWie91]

P. van Oorschot and M. Wiener, “A known plaintext attack on two-key
triple encryption”, Advances in Cryptology, EUROCRYPT ’90 (LNCS
473), 318-325, 1991.

[X9.31]

American National Standard (ANS) X9.31-1998, Digital Signatures
Using Reversible Public Key Cryptography for the Financial Services
Industry (rDSA), Withdrawn, but available from X9.org.

[X9.62]

American National Standard X9.62-2005, Public Key Cryptography for
the Financial Services Industry: The Elliptic Curve Digital Signature
Algorithm (ECDSA).

23