Re: [TLS] Collisions (Re: Nico's suggestions - Re: Consensus Call:

Marsh Ray <marsh@extendedsubset.com> Wed, 12 May 2010 14:48 UTC

Return-Path: <marsh@extendedsubset.com>
X-Original-To: tls@core3.amsl.com
Delivered-To: tls@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id DF15B28C240 for <tls@core3.amsl.com>; Wed, 12 May 2010 07:48:44 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.751
X-Spam-Level:
X-Spam-Status: No, score=-1.751 tagged_above=-999 required=5 tests=[AWL=0.848, BAYES_00=-2.599]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NXWFtBMHn8ri for <tls@core3.amsl.com>; Wed, 12 May 2010 07:48:44 -0700 (PDT)
Received: from mho-02-ewr.mailhop.org (mho-02-ewr.mailhop.org [204.13.248.72]) by core3.amsl.com (Postfix) with ESMTP id BA35C28C370 for <tls@ietf.org>; Wed, 12 May 2010 07:33:32 -0700 (PDT)
Received: from xs01.extendedsubset.com ([69.164.193.58]) by mho-02-ewr.mailhop.org with esmtpa (Exim 4.68) (envelope-from <marsh@extendedsubset.com>) id 1OCCzu-000Hvl-Uu; Wed, 12 May 2010 14:33:19 +0000
Received: from [127.0.0.1] (localhost [127.0.0.1]) by xs01.extendedsubset.com (Postfix) with ESMTP id A3A88631D; Wed, 12 May 2010 14:33:14 +0000 (UTC)
X-Mail-Handler: MailHop Outbound by DynDNS
X-Originating-IP: 69.164.193.58
X-Report-Abuse-To: abuse@dyndns.com (see http://www.dyndns.com/services/mailhop/outbound_abuse.html for abuse reporting information)
X-MHO-User: U2FsdGVkX1+S5fwZHyZoDNxnJDqyRk9h/M4suEA03ek=
Message-ID: <4BEABC2C.6090507@extendedsubset.com>
Date: Wed, 12 May 2010 09:33:16 -0500
From: Marsh Ray <marsh@extendedsubset.com>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1.8) Gecko/20100216 Thunderbird/3.0.2
MIME-Version: 1.0
To: Simon Josefsson <simon@josefsson.org>
References: <20100510221531.GC9429@oracle.com> <201005111339.o4BDdoYQ009725@fs4113.wdf.sap.corp> <20100511152153.GF9429@oracle.com> <201005111803.o4BI3fhO006065@stingray.missi.ncsc.mil> <20100511190958.GR9429@oracle.com> <4BE9B0BC.2000101@extendedsubset.com> <20100511194620.GU9429@oracle.com> <4BE9B856.40000@extendedsubset.com> <20100511200728.GW9429@oracle.com> <4BE9CC88.6040103@extendedsubset.com> <87aas5sbzy.fsf@mocca.josefsson.org>
In-Reply-To: <87aas5sbzy.fsf@mocca.josefsson.org>
X-Enigmail-Version: 1.0.1
OpenPGP: id=1E36DBF2
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: "Kemp, David P." <DPKemp@missi.ncsc.mil>, tls@ietf.org
Subject: Re: [TLS] Collisions (Re: Nico's suggestions - Re: Consensus Call:
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.9
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/listinfo/tls>, <mailto:tls-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/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, 12 May 2010 14:48:45 -0000

On 5/12/2010 4:30 AM, Simon Josefsson wrote:
> Marsh Ray <marsh@extendedsubset.com> writes:
> 
>> Alternatively, if we determine that indeed the non-collision-resistance
>> of the hash function is the root of all remaining concerns that would be
>> very positive. We could solve them all in one stroke with
>> s/FNV-1a/SHA-256/g.
> 
> If collision-resistance is a required property (I'm not convinced yet),
> I believe we need hash agility for the possibility that SHA-256 is weak.

But perhaps that agility already exists in the form of the protocol
version negotiation.

TLS 1.2 appears to effectively depend on SHA-256 (at least in HMAC form)
for the PRF. If that gets broken, we can probably not trust anything
else negotiated in the handshake and a rev of the base protocol will be
required to fix it anyway.

If bare SHA-256 is a concern, the hash could be defined as something
like hmac_sha256("Cached Info", object_bytes).

Just a thought.

- Marsh