digest data types?

I've asked a question about message digests data types on pgsql-general
several times. No one's answered. It reminds me of a childhood refrain
"No one likes me, everyone hates me, I'm going to eat some worms".
Anyway, I'm reposting the question here.

Does anyone have postgresql types for message digests, especially md5
and sha1?

Obviously I could store these as text (as I currently do), but I'm
particularly interested in custom types that store digests as binary
blobs and provide conversion to/from text.

Am I correct in assuming that the space saved by storing digests as
binary (1/2 size of hex) will substantially impact index ins/upd/del
performance or when the digest itself is a large fraction of the rest of
the row size?

Thanks,
Reece

--
Reece Hart, http://harts.net/reece/, GPG:0x25EC91A0