To: lwn@lwn.net
Subject: http://www.lwn.net/2000/0309/security.phtml
From: Florian Weimer <Florian.Weimer@RUS.Uni-Stuttgart.DE>
Date: 10 Mar 2000 18:57:13 +0100

| Duplicate key IDs for PGP-signed mail. 
| 
| Povl H. Pedersen posted a note to BugTraq describing the discovery of
| a duplicate key ID when a friend of his was verifying a PGP-signed
| email address. "The problem is, that the PGP servers expects all key
| IDs to be unique numbers, and does not expect 2 users to have the same
| keyID. And with the current amount of users, we are starting to get
| multiple users with the same keyID."

The problem that Povl observed was likely quite different.  According
to my own tests, NAI's server simply returned the wrong key, which
didn't share any characteristics with the one he requested (both key
ID and user ID were different).

Currently, I'm unable to reproduce the behavior of NAI's server, but
I've contacted them and hope that they can clarify what was really
going on.

| This issue will need to be dealt with, and quickly. The existence of a
| duplicate key ID could allow falsified mail. If a duplicate key ID can
| be generated by accident, presumably it can also be generated on
| purpose, as well. Network Associates was not directly informed of the
| problem, which was posted today, so no response from them is yet
| availab

Duplicate key IDs should pose no problem to RFC 2440 compliant OpenPGP
implementations.  Even if user IDs (i.e. the name and email address
which is associated with a PGP key) are faked in addtion to the key
ID, a user can tell a faked from a valid one by either verifying the
key length, ID and fingerprint over a reliable medium, or he can use
certificates to build a chain of trust to the right key.  After all,
faked keys are exactly the reason why we need a web of certificates.

In short, this is nothing to worry about as long as the OpenPGP is
correctly implemented and used.

-- 
Florian Weimer 	                  Florian.Weimer@RUS.Uni-Stuttgart.DE
University of Stuttgart           http://cert.uni-stuttgart.de/
RUS Security Team                 +49-711-685-5973/fax +49-711-685-5898
http://ca.uni-stuttgart.de:11371/pks/lookup?op=get&search=0xC06EC3B5