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.
