Re: [Sip] Using TLS in the first hop - Bug in RFC 5630

Iñaki Baz Castillo <ibc@aliax.net> Thu, 15 September 2011 14:28 UTC

Return-Path: <ibc@aliax.net>
X-Original-To: sip@ietfa.amsl.com
Delivered-To: sip@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A502021F8B4B for <sip@ietfa.amsl.com>; Thu, 15 Sep 2011 07:28:43 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.648
X-Spam-Level:
X-Spam-Status: No, score=-2.648 tagged_above=-999 required=5 tests=[AWL=0.029, BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, MIME_8BIT_HEADER=0.3, RCVD_IN_DNSWL_LOW=-1]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id MJsh0BNLpyJN for <sip@ietfa.amsl.com>; Thu, 15 Sep 2011 07:28:43 -0700 (PDT)
Received: from mail-qy0-f172.google.com (mail-qy0-f172.google.com [209.85.216.172]) by ietfa.amsl.com (Postfix) with ESMTP id 1668021F8B28 for <sip@ietf.org>; Thu, 15 Sep 2011 07:28:43 -0700 (PDT)
Received: by qyk32 with SMTP id 32so5096944qyk.10 for <sip@ietf.org>; Thu, 15 Sep 2011 07:30:52 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.229.67.105 with SMTP id q41mr932833qci.216.1316097052508; Thu, 15 Sep 2011 07:30:52 -0700 (PDT)
Received: by 10.229.79.207 with HTTP; Thu, 15 Sep 2011 07:30:52 -0700 (PDT)
In-Reply-To: <CALiegfkqnVMHSZuim33XNy8rPdBRmJsB6VRxF3mR1dEXvEdK-Q@mail.gmail.com>
References: <CALiegfkNfJ7McZAA=a5ajYVzYtmAjC_KQdK1P_ez2L1dia5v2g@mail.gmail.com> <CFFC2869-C704-423E-974D-3F4B93145BBB@edvina.net> <CALiegfnh2C3GNddnneepcVsGgtOd1pSDBVC3uH72S1KaVT_jHg@mail.gmail.com> <7889A6C3D41A49439DAECC7B4C998F011C07F2E6EF@MCHP058A.global-ad.net> <CALiegfkqnVMHSZuim33XNy8rPdBRmJsB6VRxF3mR1dEXvEdK-Q@mail.gmail.com>
Date: Thu, 15 Sep 2011 16:30:52 +0200
Message-ID: <CALiegf=jX6pkdw+xYueuEjgAoo_9XVhYqOgc0Uwx2yt7gqto1Q@mail.gmail.com>
From: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <ibc@aliax.net>
To: "Horvath, Ernst" <ernst.horvath@siemens-enterprise.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Cc: "sip@ietf.org" <sip@ietf.org>
Subject: Re: [Sip] Using TLS in the first hop - Bug in RFC 5630
X-BeenThere: sip@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Session Initiation Protocol <sip.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/sip>, <mailto:sip-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/sip>
List-Post: <mailto:sip@ietf.org>
List-Help: <mailto:sip-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/sip>, <mailto:sip-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 15 Sep 2011 14:28:43 -0000

2011/9/15 Iñaki Baz Castillo <ibc@aliax.net>et>:
>> It may work for the 1st request. But in a subsequent mid-dialog request in the reverse direction the contact URI becomes the Request-URI, which is now SIPS, and therefore the Contact in this request must also become SIPS, and you end up in an all-SIPS case.

This is not true. The in-dialog request will have, indeed, a RURI with
SIPS schema, but it will also contain a top Route with SIP schema, so
it takes preference and there is no need at all to set a SIPS Contact
URI.

RFC 5630:

5.1.2.  UAS Behavior

   When presented with a SIPS URI, a UAS MUST NOT change it to a SIP
   URI.

   As mandated by [RFC3261], Section 12.1.1:

      If the request that initiated the dialog contained a SIPS URI in
      the Request-URI or in the top Record-Route header field value, if
      there was any, or the Contact header field if there was no Record-
      Route header field, the Contact header field in the response MUST
      be a SIPS URI.

In our case *there is* a Record-Route in the INVITE arriving to the
UAS and it does contain a SIP URI, so the Contact in the response from
the UAS does not need to be a SIPS URI.


Anyhow I insist: SIPS and TLS usage is a pain. Nobody understands it
(it's clear given any mail thread about this topic) and everybody does
wrong assumptions. I think SIP authors should worry about this reality
and react.


Regards.


-- 
Iñaki Baz Castillo
<ibc@aliax.net>