Allowing "duplicate" signatures

David Shaw dshaw at
Mon Aug 6 17:08:01 CEST 2001

On Mon, Aug 06, 2001 at 09:46:47AM +0100, Matthew Byng-Maddick wrote:
> On Sun, Aug 05, 2001 at 07:02:50PM -0400, Michael Young wrote:
> > As it stands, GnuPG refuses to sign a key/name pair with a particular
> > key if a signature by that signing-key already exists.  There are
> > several reasons that you might want to do that, though.  As noted
> > in the code, the existing signature could be revoked.  Similarly,
> > it could be expired.  You might also want to generate a new
> > signature with new properties (subpacket values):
> >     new expiration time;
> >     new signature type (not yet selectable, but I'd like it to be);
> >     different notation data;
> Yes, definitely. If the patches posted here that I've written or something
> similar gets included in GnuPG, then there is value in being able to add
> and revoke signatures with various different notation data in them.

A problem here is that the OpenPGP spec has no notion of revocation of
a specific signature.  A revocation is actually another signature that
in effect says "I *DON'T* certify this key".  There is no way to
specify which of multiple possible signatures from a given key it is
intended to revoke.

Trust-wise, the calculation has to match up the valid sigs with valid
revocations (the time stamp can help here to a certain degree) and see
if there are more sigs than revocations.

I suppose it could be said that if a given revocation signature
matches the original signature in all subpackets except for the
signature type being set to revoke (0x30) then the revocation should
apply to the particular signature that was matched.  That's out of my
head, and not in the RFC though.


   David Shaw  |  dshaw at  |  WWW
   "There are two major products that come out of Berkeley: LSD and UNIX.
      We don't believe this to be a coincidence." - Jeremy S. Anderson

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