e)
               (ironclad:byte-array-to-hex-string digest))))</PRE><H2 ID="macs">Message authentication codes</H2><P>A message authentication code is a cryptographic function of some
data and a user-specified key.  Only a person knowing the key can
recompute the MAC for the given message.  A MAC is useful where
maintaining data integrity is required, but the secrecy of the data is
not paramount.</P><P>Ironclad provides two different kinds of MACs: HMACs, specified in
<A HREF="http://www.ietf.org/rfc/rfc21