[[meta title="MonkeySphere can't deal with passphrase-locked primary keys"]]

At the moment, the only tool we have to export passphrase-locked
secret keys from the GPG keyring is `gpg` itself (and `gpg2`, which
has roughly the same behavior).

As a result, we have the `seckey2sshagent` hack, which is unfriendly
and awkward to use.

Ideally, `openpgp2ssh` would be able to convert passphrase-locked
secret keys into clean subkeys.  However, i've tried to do this via
GnuTLS, and that library is not ready for this.

OpenCDK, which is the component of GnuTLS which reads OpenPGP-style
keys, cannot cope with encrypted secret key material.  I have had
[some
success](http://lists.gnu.org/archive/html/gnutls-devel/2008-06/msg00092.html)
in getting GnuTLS's OpenCDK to accept the existence of encrypted
secret key packets, [i learned that OpenCDK as included in GnuTLS is
incapable of dealing with the encrypted packets
themselves](http://lists.gnu.org/archive/html/gnutls-devel/2008-07/msg00012.html).


Some possible resolutions:

---------

If we can assume that the passphrase-encrypted key we want to use is
actually a subkey, and if we could fix GnuTLS to ignore the use of the
"gnu-dummy S2K" produced by `gpg --export-secret-subkeys` for the
primary key, then something like the following script should actually
work for reasonable values of `$KEYID`:

	TMPDIR=$(mktemp -d)
	umask 077
	mkfifo "$TMPDIR/passphrase"
	kname="MonkeySphere Key $KEYID"
	mkfifo "$TMPDIR/$kname"
	ssh-askpass "Please enter the passphrase for MonkeySphere key $KEYID" >"$TMPDIR/passphrase" &
	gpg  --passphrase-fd 3 3<"$TMPDIR/passphrase" \
	  --export-options export-reset-subkey-passwd,export-minimal,no-export-attributes \
	  --export-secret-subkeys "$KEYID"\! | openpgp2ssh "$KEYID" > "$TMPDIR/$kname" &
	(cd "$TMPDIR" && ssh-add -c "$kname")
	rm -rf "$TMPDIR"	

Good news!  [I've crafted a patch for GnuTLS to enable it to read
exported subkeys using this GNU
extension](http://lists.gnu.org/archive/html/gnutls-devel/2008-08/msg00005.html),
so if we can get it incorporated into upstream (and/or into debian),
we have a possible solution, as long as the authentication key is a
subkey, and not a primary key.

As of version 0.11-1, `monkeysphere subkey-to-ssh-agent` implements
this particular strategy (and fails cleanly if the version of GnuTLS
present doesn't support the GNU dummy S2K extension).

---------

Ben Laurie and Rachel Willmer's
[OpenPGPSDK](http://openpgp.nominet.org.uk) is a candidate: this is a
C-based library that intends to implement RFC 4880 functionality.

We could potentially re-write `openpgp2ssh` using this library, and it
*should* be able to handle everything we need from the OpenPGP side
(though it might need to be re-linked to OpenSSL to handle PEM-encoded
exports.

Concerns:

* OpenPGPSDK is not in debian yet, and doesn't currently (2008-08-13)
  build with gcc 4.2 or 4.3.

* OpenPGPSDK uses the apache license and appears to link to OpenSSL,
  which has a GPL-incompatible license.  I think this would mean that
  `openpgp2ssh` could not remain GPL (though the rest of the
  monkeysphere could).

---------

We could try to use perl.  The last time i checked, the pure-perl
OpenPGP implementations all depended on Math::PARI, which [is not in
debian](http://bugs.debian.org/440527).  The most likely candidate is
[Crypt::OpenPGP](http://search.cpan.org/~btrott/Crypt-OpenPGP),
despite [some
bugginess](http://cpanratings.perl.org/dist/Crypt-OpenPGP).  

Concerns:

* the aforementioned buggy reviews

* there's a lot of dependency chasing to get anything like this
  available in debian.

---------

Other alternatives?

--------

Can this bug be closed? dkg [reported in a comment for a related
bug](/bugs/install-seckey2sshagent-in-usr-bin/):

	Version 0.11-1 now has the monkeysphere subkey-to-ssh-agent
	subcommand, which works cleanly in the presence of a
	functionally-patched GnuTLS.

--------

Even with the patched GnuTLS, monkeysphere currently can't currently
deal with passphrase-locked primary keys.  I've changed the title of
this bug, but i'd like to keep it open until we are able to deal with
that.  The other comments here seem still quite relevant to that
need.

I've changed the title of this bug to reflect the narrowed scope.

       --dkg