Subject: multiple signature packets

From: <[email-masked]>
Date: Mon, 4 Aug 2003 14:41:18 -0700

have recently received a clearsigned PGP message that was signed
simultaneously with two different PGP keys,
but it caused 6.5.8ckt (build 8) to crash

the double signed messages can easily be generated from gnupg (command
line only),
but (afaik) not from pgp, even from the command line (2.x or 6.x)

have put up examples here:
http://www.angelfire.com/pr/pgpf/dspm.html

have found that the double signed messages were not a problem in pgp
8
under any circumstances,
and were not a problem for 6.5.8 as long as they weren't clearsigned

would like to request confirmation of this from anyone who uses 6.5.8
or 7.x

the double signed message can be very useful in the following specific
situation:

if someone wants to sign and encrypt to two different people, but, for
whatever reason, 
exchanged one key with one recipient and another key with another, and
doesn't want to have the keys uploaded to a server,

then, by double signing, the sender can have the message verified
independently with different keys for different receivers

{sort of cool, actually,   i wish it could be done from pgp ;-)   }

are multiple simultaneous signatures acceptable Open PGP behavior ?

tia,

vedaal

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From: Jon Callas <[email-masked]>
Date: Mon, 04 Aug 2003 17:02:07 -0700

> are multiple simultaneous signatures acceptable Open PGP behavior ?

I almost said no.

However, the grammar says yes.

   OpenPGP Message :- Encrypted Message | Signed Message |
                      Compressed Message | Literal Message.

   Compressed Message :- Compressed Data Packet.

   Literal Message :- Literal Data Packet.

   ESK :- Public Key Encrypted Session Key Packet |
          Symmetric-Key Encrypted Session Key Packet.

   ESK Sequence :- ESK | ESK Sequence, ESK.

   Encrypted Data :- Symmetrically Encrypted Data Packet |
         Symmetrically Encrypted Integrity Protected Data Packet

   Encrypted Message :- Encrypted Data | ESK Sequence, Encrypted Data.

   One-Pass Signed Message :- One-Pass Signature Packet,
               OpenPGP Message, Corresponding Signature Packet.

   Signed Message :- Signature Packet, OpenPGP Message |
               One-Pass Signed Message.

    Jon

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From: David Shaw <[email-masked]>
Date: Mon, 4 Aug 2003 20:03:57 -0400

On Mon, Aug 04, 2003 at 02:41:18PM -0700, [email-masked] wrote:
> 8 under any circumstances, and were not a problem for 6.5.8 as long
> as they weren't clearsigned

[..]

> are multiple simultaneous signatures acceptable Open PGP behavior ?

The first example you gave was of a nested one-pass signature, and the
second example was a clearsigned message with two signatures after it.

While it is unfortunate that 6.5.8 can't handle them, both of these
constructions are legal in OpenPGP (as per sections 5.4 and 7).

David