Re: [TLS] Are we holding TLS wrong?

Juliusz Chroboczek <jch@irif.fr> Fri, 09 November 2018 16:11 UTC

Return-Path: <jch@irif.fr>
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 055D3130E25; Fri, 9 Nov 2018 08:11:03 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.901
X-Spam-Level:
X-Spam-Status: No, score=-1.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, 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 09syzi8cKLps; Fri, 9 Nov 2018 08:11:00 -0800 (PST)
Received: from korolev.univ-paris7.fr (korolev.univ-paris7.fr [IPv6:2001:660:3301:8000::1:2]) (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 3E43A12D4F0; Fri, 9 Nov 2018 08:11:00 -0800 (PST)
Received: from potemkin.univ-paris7.fr (potemkin.univ-paris7.fr [IPv6:2001:660:3301:8000::1:1]) by korolev.univ-paris7.fr (8.14.4/8.14.4/relay1/82085) with ESMTP id wA9GApTc015954 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Fri, 9 Nov 2018 17:10:51 +0100
Received: from mailhub.math.univ-paris-diderot.fr (mailhub.math.univ-paris-diderot.fr [81.194.30.253]) by potemkin.univ-paris7.fr (8.14.4/8.14.4/relay2/82085) with ESMTP id wA9GArMU004301; Fri, 9 Nov 2018 17:10:53 +0100
Received: from mailhub.math.univ-paris-diderot.fr (localhost [127.0.0.1]) by mailhub.math.univ-paris-diderot.fr (Postfix) with ESMTP id 8AA8F66C91; Fri, 9 Nov 2018 17:10:57 +0100 (CET)
X-Virus-Scanned: amavisd-new at math.univ-paris-diderot.fr
Received: from mailhub.math.univ-paris-diderot.fr ([127.0.0.1]) by mailhub.math.univ-paris-diderot.fr (mailhub.math.univ-paris-diderot.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id Hj1zf9_mPRpe; Fri, 9 Nov 2018 17:10:55 +0100 (CET)
Received: from lanthane.irif.fr (unknown [172.23.36.89]) (Authenticated sender: jch) by mailhub.math.univ-paris-diderot.fr (Postfix) with ESMTPSA id 6FDE766C8D; Fri, 9 Nov 2018 17:10:54 +0100 (CET)
Date: Fri, 09 Nov 2018 17:10:54 +0100
Message-ID: <87wopmw7sh.wl-jch@irif.fr>
From: Juliusz Chroboczek <jch@irif.fr>
To: Martin Thomson <martin.thomson@gmail.com>
Cc: dschinazi.ietf@gmail.com, "<tls@ietf.org>" <tls@ietf.org>, draft-ietf-babel-dtls@ietf.org
In-Reply-To: <CABkgnnWF6_cqhMCKMWHYNcdOTU=4BjRYaYMtfz-A3jtxprRAHA@mail.gmail.com>
References: <CAPDSy+7-ceNNLJpFK0Z4SitBaUgxTpxiea8Z0QtpeSr+MNLKFg@mail.gmail.com> <CABkgnnWF6_cqhMCKMWHYNcdOTU=4BjRYaYMtfz-A3jtxprRAHA@mail.gmail.com>
User-Agent: Wanderlust/2.15.9
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (korolev.univ-paris7.fr [IPv6:2001:660:3301:8000::1:2]); Fri, 09 Nov 2018 17:10:51 +0100 (CET)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (potemkin.univ-paris7.fr [194.254.61.141]); Fri, 09 Nov 2018 17:10:53 +0100 (CET)
X-Miltered: at korolev with ID 5BE5B18B.000 by Joe's j-chkmail (http : // j-chkmail dot ensmp dot fr)!
X-Miltered: at potemkin with ID 5BE5B18D.000 by Joe's j-chkmail (http : // j-chkmail dot ensmp dot fr)!
X-j-chkmail-Enveloppe: 5BE5B18B.000 from potemkin.univ-paris7.fr/potemkin.univ-paris7.fr/null/potemkin.univ-paris7.fr/<jch@irif.fr>
X-j-chkmail-Enveloppe: 5BE5B18D.000 from mailhub.math.univ-paris-diderot.fr/mailhub.math.univ-paris-diderot.fr/null/mailhub.math.univ-paris-diderot.fr/<jch@irif.fr>
X-j-chkmail-Score: MSGID : 5BE5B18B.000 on korolev.univ-paris7.fr : j-chkmail score : . : R=. U=. O=. B=0.000 -> S=0.000
X-j-chkmail-Score: MSGID : 5BE5B18D.000 on potemkin.univ-paris7.fr : j-chkmail score : . : R=. U=. O=. B=0.000 -> S=0.000
X-j-chkmail-Status: Ham
X-j-chkmail-Status: Ham
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/AJ7hfcWaf46giBwnBnlMUKLtBxs>
Subject: Re: [TLS] Are we holding TLS wrong?
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.29
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: Fri, 09 Nov 2018 16:11:03 -0000

> I'm somewhat dismayed by the firm recommendation to use the HMAC
> mechanism,

Yeah, this could probably be loosened somewhat.

> which doesn't seem particularly robust.

It's designed to be fairly robust.  Of course, we may have done things
wrong.

> Offhand, it seems like replays are possible if you allow the possibility
> of the node crashing and dumping state.

Unless I've missed something -- they are not, assuming you have
a sufficiently strong random number generator.  The challenge mechanism
rebuilds the shared state in a secure manner, and the index mechanism
ensures that an (index, seqno) pair is never reused.

> The same applies during a rollover of the 32-bit counter.

You generate a new index when the counter overflows, and send a new
challenge.  First point of Section 4.2 of the HMAC draft.

-- Juliusz