GCM and GMAC
This is an implementation of the GCM encryption mode for use with the
AES block cipher. GCM is a general-purpose encryption mode that uses
a block cipher to provide both data confidentiality and data integrity
in a single, easy to use construct. It provides these services in a
way that is provably secure to very high levels of assurance under a
standard assumption that the underlying block cipher exhibits
pseudo-random behavior (this assumption is widely believed to be true,
but will probably never be proven).
GCM is a building block upon which one can easily build secure
channels. One need only add authentication, key agreement and
prevention against capture-replay attacks.
The Zork GCM implementation is in the public domain.