Re: [TLS] Justification

Nicolas Williams <Nicolas.Williams@oracle.com> Mon, 17 May 2010 15:46 UTC

Return-Path: <Nicolas.Williams@oracle.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 8E1803A6D4C for <tls@core3.amsl.com>; Mon, 17 May 2010 08:46:57 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.994
X-Spam-Level:
X-Spam-Status: No, score=-3.994 tagged_above=-999 required=5 tests=[AWL=0.004, BAYES_50=0.001, RCVD_IN_DNSWL_MED=-4, UNPARSEABLE_RELAY=0.001]
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 enHafB2oktKQ for <tls@core3.amsl.com>; Mon, 17 May 2010 08:46:56 -0700 (PDT)
Received: from rcsinet10.oracle.com (rcsinet10.oracle.com [148.87.113.121]) by core3.amsl.com (Postfix) with ESMTP id DE49C3A6D4D for <tls@ietf.org>; Mon, 17 May 2010 08:44:31 -0700 (PDT)
Received: from acsinet15.oracle.com (acsinet15.oracle.com [141.146.126.227]) by rcsinet10.oracle.com (Switch-3.4.2/Switch-3.4.1) with ESMTP id o4HFiLmq027093 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 17 May 2010 15:44:22 GMT
Received: from acsmt353.oracle.com (acsmt353.oracle.com [141.146.40.153]) by acsinet15.oracle.com (Switch-3.4.2/Switch-3.4.1) with ESMTP id o4HEv8ei009425; Mon, 17 May 2010 15:44:17 GMT
Received: from abhmt017.oracle.com by acsmt355.oracle.com with ESMTP id 247215481274111002; Mon, 17 May 2010 08:43:22 -0700
Received: from oracle.com (/129.153.128.104) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 17 May 2010 08:43:19 -0700
Date: Mon, 17 May 2010 10:43:15 -0500
From: Nicolas Williams <Nicolas.Williams@oracle.com>
To: Marsh Ray <marsh@extendedsubset.com>
Message-ID: <20100517154314.GU9429@oracle.com>
References: <004901caf1ea$783e23a0$68ba6ae0$@briansmith.org> <p2xa84d7bc61005120858v2ce68cf7xe6ddf559faf4d4b0@mail.gmail.com> <4BEAE4CF.7070205@pobox.com> <p2ga84d7bc61005121033n169fc0fdyb2bc94b504f3fc2c@mail.gmail.com> <20100512180814.GI9429@oracle.com> <4BEAF1F8.4030004@pobox.com> <20100512182827.GJ9429@oracle.com> <4BEAF52B.9090801@pobox.com> <20100512184257.GL9429@oracle.com> <4BEB0598.9070209@extendedsubset.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4BEB0598.9070209@extendedsubset.com>
User-Agent: Mutt/1.5.20 (2010-03-02)
X-Auth-Type: Internal IP
X-Source-IP: acsinet15.oracle.com [141.146.126.227]
X-CT-RefId: str=0001.0A090207.4BF16457.00A2:SCFMA922111,ss=1,fgs=0
Cc: tls@ietf.org
Subject: Re: [TLS] Justification
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: Mon, 17 May 2010 15:46:57 -0000

On Wed, May 12, 2010 at 02:46:32PM -0500, Marsh Ray wrote:
> On 5/12/2010 1:42 PM, Nicolas Williams wrote:
> > Paul Hoffman proposes an extension to add inputs to the Finished message
> > computation.  There's no objection yet to Paul's proposal on the grounds
> > you state.
> 
> I'm not sure the discussion got that far, so it's not evidence of much.

Fair enough.

> > In any case, one of the problems with the caching extension as proposed
> > result from not binding the cached objects to the Finished message,
> > which at the very least complicates the security analysis of the
> > protocol, and possibly compromises it altogether.  We MUST NOT make the
> > same mistakes we've made before.
> 
> Agreed, but we should be just as careful not to make new ones.

How could binding the cached objects into the handshake be a new mistake
given that we bind them in now?

> Sorry if you explained this earlier, but how would the "use URLs"
> approach be different than an arbitrary server-chosen identifier?

URIs would be useable across many servers, as opposed to server-assigned
IDs.  But this is not important.

I don't care how the objects are named.  I care only that they be bound
into the handshake.

(Earlier I had thought that we could avoid the SHA-1 vs. FNV-1a issue by
having server-assigned object IDs, however, that was incorrect.  It's
not how we name the objects but how we agree that two peers have the
same cached/cacheable objects that matters.  I'm sorry I even mentioned
server-assigned object IDs.  If I'd thought about it longer I'd have
understood the real problem earlier and avoided this little detour.)

Nico
--