NISTIR 7863

Cardholder Authentication for the 

PIV Digital Signature Key

W. Timothy Polk

Hildegard Ferraiolo

David Cooper

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.IR.7863
NISTIR 7863

Cardholder Authentication for the 

PIV Digital Signature Key

W. Timothy Polk

Hildegard Ferraiolo

David Cooper

Computer Security Division

Information Technology Laboratory

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.IR.7863

June 2015

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
ii

National Institute of Standards and Technology Internal Report 7863

9 pages (June 2015)

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.IR.7863

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. All NIST Computer Security Division publications, other than the ones noted above, are available at 

http://csrc.nist.gov/publications. 

Comments on this publication may be submitted to:

National Institute of Standards and Technology

Attn: Computer Security Division, Information Technology Laboratory

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

Email: piv_comments@nist.gov
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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.

Abstract

FIPS 201-2 requires explicit user action by the Personal Identity Verification (PIV) cardholder as a 

condition for use of the digital signature key stored on the card. This document clarifies the requirement 

for explicit user action to encourage the development of compliant applications and middleware that use 

the digital signature key.

Keywords

personal identification number; personal identity verification; PIN caching; PIV
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Table of Contents

1. INTRODUCTION ...................................................................................................................................1

2. BACKGROUND .....................................................................................................................................1

3. ARCHITECTURES.................................................................................................................................2

4. MINIMUM SECURITY OBJECTIVES & CONTROLS.............................................................................2

4.1 Per-Transaction PIN Entry ..........................................................................................................2

4.2 Explicit User Action with PIN Caching ......................................................................................2

APPENDIX A— ACRONYMS.........................................................................................................................4

APPENDIX B— REFERENCES ......................................................................................................................4
NISTIR 7863 Cardholder Authentication for the PIV Digital Signature Key

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1. Introduction

Federal Information Processing Standard (FIPS) 201 defines the Personal Identity Verification 

(PIV) Card and supporting process requirements. A private cryptographic key, the digital 

signature key (DSK), is specified for digitally signing messages and data. The DSK is generated 

on the card and is never exported; all operations with this private key are performed by the PIV 

Card. FIPS 201 requires authentication of the cardholder via “explicit user action” each time the 

DSK is used to perform a cryptographic operation.

NIST Special Publication 800-73 specifies the “PIN ALWAYS” access condition for the DSK to 

ensure that the Personal Identification Number (PIN) is submitted to the card for each requested 

cryptographic operation. However, FIPS 201 does not mandate the use of card readers with 

integrated PIN entry pads. As a result, the PIV Card itself cannot differentiate between a freshly 

supplied PIN and a PIN cached by the calling application or system.

This specification clarifies the requirement for “explicit user action” and specifies a range of 

implementation options that satisfy this requirement, in order to ensure a consistent and reliable 

level of security.

2. Background

The digital signature key (DSK) is intended to sign data, such as electronic forms, documents or 

electronic mail. Operations using the DSK can be performed after the PIV Card has been 

activated. To protect the DSK against misuse after activation, each subsequent private key 

operation requires an explicit user action. 

The PIV Card incorporates a single mechanism for both authenticating the cardholder and 

expressing explicit user action: entry of the user PIN.

1 The user PIN must be presented to the PIV 

Card to activate the card for privileged/protected operations or to perform a signing operation 

with the DSK. If the user is prompted for the PIN, and that value is presented to the PIV Card for 

each operation, the requirement for explicit user action is clearly satisfied. This ensures that the 

user is present and intended to generate a signature with the DSK each time a signature 

generation operation is performed. However, ensuring that the PIN is re-entered by the user for 

each signature operation requires system level controls outside the boundaries of the PIV Card.

In addition, for some applications it is considered impractical to require the cardholder to enter 

the PIN for each signature. For example, users may be required by policy to sign every email 

message. When the user is sending a large number of email messages in a short period, repeatedly 

entering the PIN greatly decreases usability. In such cases, the application or middleware can be

designed to retain (or cache) the smart card PIN and present it on behalf of the user. However, 

caching the PIN may allow the application or middleware to present the PIN without the 

cardholder’s knowledge.

The following sections identify possible architectures for systems that use the DSK, and define 

the minimum security objectives and controls that constitute explicit user action for the PIN 

ALWAYS access condition of the DSK.

 

1

FIPS 201-2 introduces the option for PIV Cards to implement on-card fingerprint biometric comparison, 

in addition to the PIN, as a mechanism to authenticate the cardholder to the card; however, the 

recommendations in this document only apply to the PIN.
NISTIR 7863 Cardholder Authentication for the PIV Digital Signature Key

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3. Architectures

There are two basic configurations for a PIV compliant system that leverages the DSK:

(1) A computing system can be designed so that the PIN is never exposed to the operating 

system, middleware, or applications. The components of this system are the host 

computer with an external smart card reader with keypad, and the PIV Card. In this case, 

the PIN is submitted from the user “directly” to the PIV Card. The application or 

operating system cannot cache the PIN so enforcing the PIN ALWAYS requirement is 

sufficient to confirm explicit user action for each DSK private key operation.

(2) A computing system can be designed so that the PIN is entered via the host computer’s 

keyboard. The components of this system are the host computer system with an internal 

or external smart card reader without keypad, and the PIV Card. In this case, the PIN is 

entered into the keyboard and is processed by the operating system, middleware, or 

application before submission to the PIV Card.

In configuration (1), it is the external reader’s responsibility to ensure that the PIN is supplied to 

the PIV Card as a result of an explicit action. In configuration (2), the host system software, in 

combination, has the responsibility to ensure that the PIN is supplied to the PIV Card as a result 

of an explicit action.

The following section specifies implementation guidelines for PIV system components.

4. Minimum Security Objectives & Controls

This section specifies minimum security controls and objectives for system implementations that 

leverage the DSK to ensure that each presentation of the PIN represents an explicit user action. 

Section 4.1 describes functional requirements for systems that prohibit PIN caching. Section 4.2

specifies the minimum security objectives and controls for system implementations that support 

DSK PIN caching.

4.1 Per-Transaction PIN Entry

Entering the PIN each time is the most direct and strongest mechanism to achieve explicit user 

action for the PIN ALWAYS access condition of the DSK. This can be achieved by any of the 

following methods:

(1) PIN entry is performed exclusively using an external card reader with key pad,

2

and the 

card reader itself does not cache the PIN; or

(2) PIN entry is performed using the host system, and the operating system, middleware, and 

all applications are configured so that the PIN is never cached.

In combination with the PIV Card’s native controls, both solutions confirm user action for each 

DSK private key operation simply by enforcing the PIN ALWAYS requirement.

4.2 Explicit User Action with PIN Caching

If the PIN is cached by any component of the system, it is the system’s responsibility to ensure an 

explicit user action occurs before the PIN is presented to the PIV Card. Examples of affirmative 

action could include clicking “OK” in a pop-up box or by user selection of an appropriate menu 

option or commit button within the application.

PIN caching implementations for the DSK should ensure that the following are satisfied:

 

2 Note that the card reader needs to intercept and discard any Application Protocol Data Units (APDUs)

that contain the PIN originating from the host system.
NISTIR 7863 Cardholder Authentication for the PIV Digital Signature Key

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1. The PIN cache is limited to a single process or application instance. That is, a PIN 

presented by an email application to digitally sign email is not accessible to other 

applications resident on the host system, such as workflow or document signing 

applications.

2. The cached PIN is not presented to the smart card without an associated explicit user 

action. The explicit user action may be handled by either of the following methods:

a. The component that confirms the explicit user action is the component that 

caches the PIN (e.g., the application or the middleware); or

b. The programming interface between the component that confirms the explicit 

user action and the component that caches the PIN can convey the difference 

between a request associated with explicit user action and a request that was not 

associated with an explicit user action. 

3. The PIN cache is cleared if any of the following conditions apply:

a. The system is shut down or rebooted;

b. The PIV Card is removed from the system;

c. The associated process or application instance is terminated; or

d. The PIN has not been presented to the PIV Card for more than N minutes. (In 

other words, more than N minutes have passed since the user performed an 

explicit action authorizing a signature.) The value of N is an agency (or Identity, 

Credential, and Access Management Subcommittee—ICAMSC) decision but 

should not exceed thirty minutes.
NISTIR 7863 Cardholder Authentication for the PIV Digital Signature Key

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Appendix A—Acronyms

APDU Application Protocol Data Unit

DSK Digital Signature Key

FIPS Federal Information Processing Standard

ICAMSC Identity, Credential, and Access Management Subcommittee

ITL Information Technology Laboratory

NIST National Institute of Standards and Technology

NISTIR National Institute of Standards and Technology Internal Report

PIN Personal Identification Number

PIV Personal Identity Verification

SP Special Publication

Appendix B—References

[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

[SP800-73] NIST Special Publication 800-73-4, Interfaces for Personal Identity Verification,

May 2015.

http://dx.doi.org/10.6028/NIST.SP.800-73-4