I've just committed cgd, the CryptoGraphic Disk.

The cgd is basically a pseudo-disk which encrypts blocks on their
way to the disk that it is attached to.  Currently it supports 3
crypto algorithms:  aes-cbc, blowfish-cbc and 3des-cbc.  The IV is
chosen by the ``IV generation method'', the only one that is
implemented is ``encblkno'', i.e. encrypted block number.

For more information about how to use and configure cgds please
refer to the provided documentation, cgd(4) and cgdconfig(8).

--
    Roland Dowdeswell                      http://www.Imrryr.ORG/~elric/