**hmac_sha**(

`+Key, +Data, -HMAC, +Options`)

*``A keyed-hash message authentication code, or HMAC, is a type of message authentication code (MAC) calculated using a cryptographic hash function in combination with a secret key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authenticity of a message. Any iterative cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA-1 accordingly. The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, on the size and quality of the key and the size of the hash output length in bits.''*

`Key` and `Data` are either an atom, packed string
or list of character codes. `HMAC` is unified with a list of
integers representing the authentication code. `Options` is the
same as for
sha_hash/3,
but currently only `sha1`

and `sha256`

are
supported.