contrib/pgcrypto functions not IMMUTABLE?

I've noticed that contrib/pgcrypto/pgcrypto.sql.in doesn't include
a volatility category in its CREATE FUNCTION statements, so the
functions are all created VOLATILE.  Shouldn't most of them be
IMMUTABLE?  Or do the algorithms have side effects?  So far I've
found no discussion about this except for one person asking about
it last year:

http://archives.postgresql.org/pgsql-admin/2004-12/msg00065.php

-- 
Michael Fuhr
http://www.fuhr.org/~mfuhr/