Re: [openpgp] New fingerprint: which hash algo (was: to v5 or not to v5)

Simon Josefsson <simon@josefsson.org> Tue, 06 October 2015 09:03 UTC

Return-Path: <simon@josefsson.org>
X-Original-To: openpgp@ietfa.amsl.com
Delivered-To: openpgp@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 1634D1A6F93 for <openpgp@ietfa.amsl.com>; Tue, 6 Oct 2015 02:03:52 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.551
X-Spam-Level:
X-Spam-Status: No, score=-1.551 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HELO_EQ_SE=0.35, SPF_PASS=-0.001] autolearn=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 1blNLT2UXh89 for <openpgp@ietfa.amsl.com>; Tue, 6 Oct 2015 02:03:50 -0700 (PDT)
Received: from duva.sjd.se (duva.sjd.se [IPv6:2001:9b0:1:1702::100]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 62D551A6F86 for <openpgp@ietf.org>; Tue, 6 Oct 2015 02:03:49 -0700 (PDT)
Received: from latte.josefsson.org ([155.4.17.3]) (authenticated bits=0) by duva.sjd.se (8.14.4/8.14.4/Debian-4) with ESMTP id t9693WJe032728 (version=TLSv1/SSLv3 cipher=AES128-GCM-SHA256 bits=128 verify=NOT); Tue, 6 Oct 2015 11:03:33 +0200
Date: Tue, 6 Oct 2015 11:03:30 +0200
From: Simon Josefsson <simon@josefsson.org>
To: Tom Ritter <tom@ritter.vg>
Message-ID: <20151006110330.38b38ea4@latte.josefsson.org>
In-Reply-To: <CA+cU71n1OUq4TtmY+8S2yfu2bvjAr+=DwtN-4xRW4xitjDpFXg@mail.gmail.com>
References: <878u84zy4r.fsf@vigenere.g10code.de> <55FD7CF0.8030200@iang.org> <87io742kz7.fsf@latte.josefsson.org> <87mvw4ctv5.fsf_-_@vigenere.g10code.de> <CA+cU71n1OUq4TtmY+8S2yfu2bvjAr+=DwtN-4xRW4xitjDpFXg@mail.gmail.com>
X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu)
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256; boundary="Sig_/KTo922B.AG3JusNSwa7949H"; protocol="application/pgp-signature"
X-Virus-Scanned: clamav-milter 0.98.7 at duva.sjd.se
X-Virus-Status: Clean
Archived-At: <http://mailarchive.ietf.org/arch/msg/openpgp/y7RkyYc5iuTT9WG_StgOCCGZj_Y>
Cc: IETF OpenPGP <openpgp@ietf.org>, ianG <iang@iang.org>
Subject: Re: [openpgp] New fingerprint: which hash algo (was: to v5 or not to v5)
X-BeenThere: openpgp@ietf.org
X-Mailman-Version: 2.1.15
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, 06 Oct 2015 09:03:52 -0000

> On 30 September 2015 at 01:18, Werner Koch <wk@gnupg.org>; wrote:
> > On Mon, 21 Sep 2015 11:13, simon@josefsson.org said:
> >
> >> Regarding which hash to use, SHA-256 is probably the simplest
> >> choice From a practicallity and consensus point of view.  Are
> >> there any strong reasons to favor something else?
> 
> I have a small preference to see the fingerprint algorithm match what
> we believe the most popular signature (hash) algorithm will be. I've
> been working with a number of embedded folks and code size can often
> be a big concern. More Algorithms, More Code.

My perception is that the most popular signature hash algorithms right
now are SHA-256 and SHA-512.  While SHA-256 and SHA-512 have somewhat
different characteristics on different platforms, I believe we are
approaching the limit of where a lot of additional comparisons are
worth the time and effort compared to just pick one of them.  I'm fine
with SHA-256 for the reasons that Werner presented.  Does someone
else want to promote another option?  Can we get closure on this?

/Simon