Re: [openpgp] Issuer Fingerprint

Werner Koch <wk@gnupg.org> Tue, 14 June 2016 13:21 UTC

Return-Path: <wk@gnupg.org>
X-Original-To: openpgp@ietfa.amsl.com
Delivered-To: openpgp@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id EED6112D6AE for <openpgp@ietfa.amsl.com>; Tue, 14 Jun 2016 06:21:42 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.9
X-Spam-Level:
X-Spam-Status: No, score=-6.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id aAjKcfJ4VGyo for <openpgp@ietfa.amsl.com>; Tue, 14 Jun 2016 06:21:39 -0700 (PDT)
Received: from kerckhoffs.g10code.com (kerckhoffs.g10code.com [IPv6:2001:aa8:fff1:100::22]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 48EA812D149 for <openpgp@ietf.org>; Tue, 14 Jun 2016 06:21:37 -0700 (PDT)
Received: from uucp by kerckhoffs.g10code.com with local-rmail (Exim 4.80 #2 (Debian)) id 1bCoHf-00074o-Et for <openpgp@ietf.org>; Tue, 14 Jun 2016 15:21:35 +0200
Received: from wk by wheatstone.g10code.de with local (Exim 4.84 #3 (Debian)) id 1bCoDd-0000Tp-Ux; Tue, 14 Jun 2016 15:17:25 +0200
From: Werner Koch <wk@gnupg.org>
To: Joseph Lorenzo Hall <joe@cdt.org>
References: <87mvmp5rmi.fsf@wheatstone.g10code.de> <CABtrr-Vrv-S_2htPECqLR+Butqr9GzwvPaXfqEyW2fBRW__o_w@mail.gmail.com>
Organisation: g10 Code GmbH
X-message-flag: Mails containing HTML will not be read! Please send only plain text.
OpenPGP: url=https://k.gnupg.net/80615870F5BAD690333686D0F2AD85AC1E42B367
Mail-Followup-To: Joseph Lorenzo Hall <joe@cdt.org>, "openpgp\@ietf.org" <openpgp@ietf.org>
Date: Tue, 14 Jun 2016 15:17:25 +0200
In-Reply-To: <CABtrr-Vrv-S_2htPECqLR+Butqr9GzwvPaXfqEyW2fBRW__o_w@mail.gmail.com> (Joseph Lorenzo Hall's message of "Tue, 14 Jun 2016 08:25:15 -0400")
Message-ID: <87mvmnyknu.fsf@wheatstone.g10code.de>
User-Agent: Gnus/5.13 (Gnus v5.13)
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Archived-At: <https://mailarchive.ietf.org/arch/msg/openpgp/43TO2VkNwUT0t0gz77oUhBaJ-uU>
Cc: "openpgp@ietf.org" <openpgp@ietf.org>
Subject: Re: [openpgp] Issuer Fingerprint
X-BeenThere: openpgp@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: "Ongoing discussion of OpenPGP issues." <openpgp.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/openpgp>, <mailto:openpgp-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/openpgp/>
List-Post: <mailto:openpgp@ietf.org>
List-Help: <mailto:openpgp-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/openpgp>, <mailto:openpgp-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 14 Jun 2016 13:21:43 -0000

On Tue, 14 Jun 2016 14:25, joe@cdt.org said:
> Sounds like it doesn't make sense to make this optional for signatures as
> implicit signature identity could result in attacks where the attacker
> changes an implicit identity and signature verification fails?

Well, it is a SHOULD feature:

   SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

I can imagine valid reasons not to use this; in particular if you want a
very short signature and the key is already known my other means.

An attacker who wants to mount a DoS can simply flip a bit in the
signature to force the verification to fail.


Shalom-Salam,

   Werner

-- 
Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.
    /* EFH in Erkrath: https://alt-hochdahl.de/haus */