Re: [TLS] Version negotiation, take two

Hubert Kario <hkario@redhat.com> Wed, 14 September 2016 18:02 UTC

Return-Path: <hkario@redhat.com>
X-Original-To: tls@ietfa.amsl.com
Delivered-To: tls@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 6692D12B40C for <tls@ietfa.amsl.com>; Wed, 14 Sep 2016 11:02:44 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -8.41
X-Spam-Level:
X-Spam-Status: No, score=-8.41 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RP_MATCHES_RCVD=-1.508, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001] 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 icfdqxk2slTH for <tls@ietfa.amsl.com>; Wed, 14 Sep 2016 11:02:40 -0700 (PDT)
Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 69A3D12B40A for <tls@ietf.org>; Wed, 14 Sep 2016 11:02:40 -0700 (PDT)
Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 32F1E66C89; Wed, 14 Sep 2016 18:02:40 +0000 (UTC)
Received: from pintsize.usersys.redhat.com ([10.34.250.200]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u8EI2cCu014813 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 14 Sep 2016 14:02:39 -0400
From: Hubert Kario <hkario@redhat.com>
To: Andrei Popov <Andrei.Popov@microsoft.com>
Date: Wed, 14 Sep 2016 20:02:31 +0200
Message-ID: <2260393.jBGLD1rnRy@pintsize.usersys.redhat.com>
User-Agent: KMail/5.2.3 (Linux/4.7.2-201.fc24.x86_64; KDE/5.26.0; x86_64; ; )
In-Reply-To: <CY1PR0301MB0842F99D7A32DFDCD18B3EAB8CF10@CY1PR0301MB0842.namprd03.prod.outlook.com>
References: <CAF8qwaA86yytg29QOD_N7ARimh9QcNGU_nnr_OrxqCrvrk2MBg@mail.gmail.com> <4707488.xUP5jY4WDA@pintsize.usersys.redhat.com> <CY1PR0301MB0842F99D7A32DFDCD18B3EAB8CF10@CY1PR0301MB0842.namprd03.prod.outlook.com>
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="nextPart2805063.7zPnQQvbDS"; micalg="pgp-sha512"; protocol="application/pgp-signature"
X-Scanned-By: MIMEDefang 2.68 on 10.5.11.23
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Wed, 14 Sep 2016 18:02:40 +0000 (UTC)
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/PelC9RFErwkD97dPQWywOt118NE>
Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Version negotiation, take two
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: "This is the mailing list for the Transport Layer Security working group of the IETF." <tls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tls>, <mailto:tls-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tls/>
List-Post: <mailto:tls@ietf.org>
List-Help: <mailto:tls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tls>, <mailto:tls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 14 Sep 2016 18:02:44 -0000

On Wednesday, 14 September 2016 17:39:59 CEST Andrei Popov wrote:
> Do you mean a TLS extension code point per TLS version?

yes, e.g. if extension 0x00a0 is present assume TLSv1.3 support, 0x0121, 
TLSv1.4; same way EMS and MtE works

> One argument against this was that this makes it difficult to express the
> client's prioritization of TLS versions, but IMHO arguably the server
> should not care.

I don't think we should depart from the "highest mutually supported version" 
negotiation algorithm, any kind of preference in the client list is likely to 
cause additional problems - version misnegotiation

if client will want to advertise support for TLSv1.3 and TLSv1.5 but not 
TLSv1.4 it will still be able to do that
 
> -----Original Message-----
> From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Hubert Kario
> Sent: Wednesday, September 14, 2016 9:40 AM
> To: David Benjamin <davidben@chromium.org>
> Cc: tls@ietf.org
> Subject: Re: [TLS] Version negotiation, take two
> 
> On Wednesday, 14 September 2016 16:17:50 CEST David Benjamin wrote:
> 
> > Yes, we find list intolerance too---servers which only look at the 
> > second byte in a cipher suite, servers which forgot a default in their 
> > NamedGroup switch-case, servers which get confused on unknown 
> > HashAlgorithms, servers which require the final extension 
> > non-empty---but this is dramatically less than version intolerance. 
> > It's usually within tolerable levels that we needn't resort to fallbacks.
> > 
> > The proposal switches from something which we know does not work to 
> > something new. Perhaps this new one will break too, but it is very 
> > similar to things that have worked before, and I am hopeful that GREASE
> > will help.
> 
> Was the option to do "one extension point = specific TLS version supported"
> 
> discussed too? What arguments are there against it?
> 
> --
> Regards,
> Hubert Kario
> Senior Quality Engineer, QE BaseOS Security team
> Web: www.cz.redhat.com
> Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic


-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic