crypto.rb, line 41 has this:

    envelope.header["Content-Type"] = 'multipart/signed;
protocol=application/pgp-signature; micalg=pgp-sha1'

that is no good if my hash algorithm is *not* sha1, which it is not. in fact,
what that creates are broken signatures, which some clients will complain about.
in fact, enigmail for one complains about them because gpg complains:

/usr/bin/gpg --charset utf8  --batch --no-tty --status-fd 2 --verify
gpg: Signature made Wed 09 Dec 2009 01:03:13 PM EST using RSA key ID 2861A790
gpg: WARNING: signature digest conflict in message
gpg: Can't check signature: general error

Sup should detect the hashing algorithm and set it properly, rather than
hardcoding it. 

RFC 3156 reads:

  The "micalg" parameter for the "application/pgp-signature" protocol
   MUST contain exactly one hash-symbol of the format "pgp-<hash-
   identifier>", where <hash-identifier> identifies the Message
   Integrity Check (MIC) algorithm used to generate the signature.
   Hash-symbols are constructed from the text names registered in [1] or
   according to the mechanism defined in that document by converting the
   text name to lower case and prefixing it with the four characters
   "pgp-".

   Currently defined values are "pgp-md5", "pgp-sha1", "pgp-ripemd160",
   "pgp-md2", "pgp-tiger192", and "pgp-haval-5-160".