digest data types?

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