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3.1 PIV Cryptographic Keys

NIST PIV and digital identity SP 800-78-4
All changes in this version
first version loaded 3 On Card Cryptographic Requirements part of 3

Title

PIV Cryptographic Keys

Control

FIPS 201-2 and SP 800-73-4 specify six different classes of cryptographic keys to be used as credentials by the PIV cardholder:

+ the mandatory PIV Authentication key;

+ the mandatory asymmetric Card Authentication key;

+ an optional symmetric Card Authentication key;

+ a conditionally mandatory digital signature key;

+ a conditionally mandatory key management key; 1 and

+ an optional asymmetric key to establish session keys for secure messaging.

Table 3-1 establishes specific requirements for cryptographic algorithms and key sizes for each key type.

In addition to the key sizes, keys must be generated using secure parameters. Rivest, Shamir, Adleman (RSA) keys must be generated using a public exponent of 65 537. Elliptic curve keys must correspond to one of the following recommended curves from [FIPS186] :

+ Curve P-256; or

+ Curve P-384.

To promote interoperability, this specification further limits PIV Authentication and Card Authentication elliptic curve keys to a single curve (P-256). 2 PIV cryptographic keys for digital signatures and key management may use P-256 or P-384, based on application requirements. There is no phase out date specified for either curve.

If the PIV Card Application supports the virtual contact interface [SP800-73] and the digital signature key, the key management key, or any of the retired key management keys are elliptic curve keys corresponding to Curve P-384, then the PIV Secure Messaging key shall use P-384, otherwise it may use P-256 or P-384.

1 The digital signature and key management keys are mandatory if the cardholder has a government-issued email account at the time of credential issuance. 2 To reduce computation times for authentication for physical access, it is recommended that the asymmetric Card Authentication key be an elliptic curve key rather than an RSA key. Table 3-1. Algorithm and Key Size Requirements for PIV Key Types

PIV Key Type Algorithms and Key Sizes PIV Authentication key RSA (2048 bits) ECDSA (Curve P-256) asymmetric Card Authentication key RSA (2048 bits) ECDSA (Curve P-256) symmetric Card Authentication key 3TDEA 3 AES-128, AES-192, or AES-256 digital signature key RSA (2048 bits) ECDSA (Curve P-256 or P-384) key management key RSA key transport (2048 bits); ECDH (Curve P-256 or P-384) PIV Secure Messaging key ECDH (Curve P-256 or P-384)

While this specification requires that the RSA public exponent associated with PIV keys be 65 537, applications should be able to process RSA public keys that have any public exponent that is an odd positive integer greater than or equal to 65 537 and less than 2 256 .

This specification requires that the key management key must be an RSA key transport key or an Elliptic Curve Diffie-Hellman (ECDH) key. The specifications for RSA key transport are [PKCS1] and [SP800-56B] ; the specification for ECDH is [SP800-56A] .