Digest::HMAC is a perl module used for message integrity checks
between two parties that share a secret key, and works in combination
with some other Digest algorithm, usually MD5 or SHA-1.  The HMAC
mechanism is described in RFC 2104.

The Digest::HMAC module follow the common Digest:: interface, but the
constructor takes the secret key and the name of some other simple
Digest:: module as argument.
