This standard describes a keyed-hash message authentication code (HMAC), a

mechanism for message authentication using cryptographic hash functions. HMAC can

be used with any iterative Approved cryptographic hash function, in combination with a

shared secret key. The cryptographic strength of HMAC depends on the properties of the

underlying hash function. The HMAC specification in this standard is a generalization of

Internet RFC 2104, HMAC, Keyed-Hashing for Message Authentication, and ANSI

X9.71, Keyed Hash Message Authentication Code.