Authentication with geom_eli

[Cyrus Rahman]

The addition of data integrity verification to geom_eli is a great
thing and very useful.

As it is implemented, it also provides some considerable measure of
authentication.  This also has utility, but for the applications I
have in mind it is less useful than either encryption or integrity
verification.

With this in mind, the addition of a less expensive authentication
algorithm, say a CRC, which would provide still provide a check on the
channel between geom_eli and the physical disk sectors without the
overhead of md5 or sha256, would be extremely useful.