HMAC

RFC2104

authentication key K

ipad - the byte 0x36 repeated B times

opad - the byte 0x5C repeated B times.

To compute HMAC over the data “text” we perform

HMAC - H(K XOR opad, H(K XOR ipad, text))

也就是用K对text做处理

H函数可选SHA1, MD5, RIPEMD, 等等

HMAC-SHA-256

RFC4868

Block size: the size of the data block the underlying hash algorithm

operates upon. For SHA-256, this is 512 bits, for SHA-384 and SHA-512, this is 1024 bits.

Output length: the size of the hash value produced by the underlying

hash algorithm. For SHA-256, this is 256 bits, for SHA-384 this is 384 bits, and for SHA-512, this is 512 bits.

Authenticator length: the size of the “authenticator” in bits. This

only applies to authentication/integrity related algorithms, and refers to the bit length remaining after truncation. In this specification, this is always half the output length of the underlying hash algorithm.

注意参看2.7.2节的示例

Block size可以padding对齐，Output length长度固定，Authenticator length取Output的前一半

doc

NIST 800-38

FIPS 198