CKM_AES_GMAC

This section provides a summary of CKM_AES_GMAC.

Supported operations

FIPS Mode support

Key size range (bytes) and parameters

Parameter

CK_GCM_PARAMS

Mechanism description

AES-GMAC is a mechanism for single and multiple-part signatures and verification described in NIST Special Publication 800-38D. GMAC is a special case of GCM that authenticates only the additional authenticated data (AAD) part of the GCM mechanism parameters. When GMAC is used with C_Sign or C_Verify, pData points to the AAD. GMAC does not use plaintext or ciphertext.

The signature produced by GMAC is also referred to as a tag.

The mechanism parameter, according to PKCS#11 2.40, is a 12 byte IV value and the tag size is a fixed 16 bytes.

The ProtectToolkit (PTK) implementation has a special feature to assist with compatibility with other implementations that use the CK_GCM_PARAMS structure as the mechanism parameter.

If the CK_GCM_PARAMS structure is passed as a parameter then:

• The tag’s length is determined by the CK_GCM_PARAMS field ulTagBits.

• The IV length is determined by the CK_GCM_PARAMS field ulIvLen.

• If any pAAD and ulAADLen are both non zero, then the AAD value will be processed before any data passed in the C_SignUpdate call; that is, the AAD value to be signed can be passed in through the CK_GCM_PARAMS or the C_SignUpdate call (or both).

Otherwise the parameter is interpreted as the IV value and the tag size will be 16 bytes.

The software emulation does not accept a raw IV value and the CK_GCM_PARAMS must be supplied by the application.

Constraints on key types and the length of data are summarized in the following table:

For this mechanism, the ulMinKeySize and ulMaxKeySize fields of the CK_MECHANISM_INFO structure are 16, 26, and 32.

Return to ProtectToolkit-C mechanisms.