This module provides common interface to HMAC functionality. HMAC is a kind of
"Message Authentication Code" (MAC) algorithm whose standard is documented in
RFC2104. Namely, a MAC provides a way to check the integrity of information
transmitted over or stored in an unreliable medium, based on a secret key.
Originally written by Daiki Ueno. Converted to a RubyGem by Geoffrey Grosenbach
Submitted by: http://ruby-hmac.rubyforge.org/