Re: [rtcweb] AVPF [was: Encryption mandate (and offer/answer)]

"Olle E. Johansson" <oej@edvina.net> Sat, 10 September 2011 07:50 UTC

Return-Path: <oej@edvina.net>
X-Original-To: rtcweb@ietfa.amsl.com
Delivered-To: rtcweb@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A3ADF21F8772 for <rtcweb@ietfa.amsl.com>; Sat, 10 Sep 2011 00:50:05 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.211
X-Spam-Level:
X-Spam-Status: No, score=-2.211 tagged_above=-999 required=5 tests=[AWL=0.038, BAYES_00=-2.599, HELO_EQ_SE=0.35]
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 JD4uE1t5lKVe for <rtcweb@ietfa.amsl.com>; Sat, 10 Sep 2011 00:50:05 -0700 (PDT)
Received: from smtp7.webway.se (smtp7.webway.se [212.3.14.205]) by ietfa.amsl.com (Postfix) with ESMTP id 536DD21F8715 for <rtcweb@ietf.org>; Sat, 10 Sep 2011 00:50:02 -0700 (PDT)
Received: from [192.168.40.24] (ns.webway.se [87.96.134.125]) by smtp7.webway.se (Postfix) with ESMTPA id 835E5754BCE4; Sat, 10 Sep 2011 07:51:55 +0000 (UTC)
Mime-Version: 1.0 (Apple Message framework v1244.3)
Content-Type: text/plain; charset=iso-8859-1
From: "Olle E. Johansson" <oej@edvina.net>
In-Reply-To: <CABcZeBOdP6cAqBoiSV-Vdv1_EK3DfgnMamT3t3ccjDOMfELfBw@mail.gmail.com>
Date: Sat, 10 Sep 2011 09:52:01 +0200
Content-Transfer-Encoding: quoted-printable
Message-Id: <16BE1F12-0AB7-45D5-BA4A-3E0A59BE1E62@edvina.net>
References: <A444A0F8084434499206E78C106220CA0B00FDB08B@MCHP058A.global-ad.net> <101C6067BEC68246B0C3F6843BCCC1E31018BF6BE2@MCHP058A.global-ad.net> <4E540FE2.7020605@alcatel-lucent.com> <2E239D6FCD033C4BAF15F386A979BF5106423F@sonusinmail02.sonusnet.com> <4E6595E7.7060503@skype.net> <4E661C83.5000103@alcatel-lucent.com> <2E239D6FCD033C4BAF15F386A979BF510F086B@sonusinmail02.sonusnet.com> <4E666926.8050705@skype.net> <43A0D702-1D1F-4B4E-B8E6-C9F1A06E3F8A@edvina.net> <033458F56EC2A64E8D2D7B759FA3E7E7020E64DC@sonusmail04.sonusnet.com> <E4EC1B17-0CC4-4F79-96DD-84E589FCC4F0@edvina.net> <4E67C3F7.7020304@jesup.org> <BE60FA11-8FFF-48E5-9F83-4D84A7FBE2BE@vidyo.com> <4E67F003.6000108@jesup.org> <7F2072F1E0DE894DA4B517B93C6A05852233E8554C@ESESSCMS0356.eemea.ericsson.se> <C3759687E4991243A1A0BD44EAC8230339CA68F054@BE235.mail.lan> <CAOJ7v-2u0UuNXh7bzmZFwiSucbsh=Ps=C3ZM5M3cJrXRmZgODA@mail.gmail.com> <CAKhHsXHXCkNdjtpxCSCk+ABbtxY15GEgouE6X6-sn-LqhnidQw@mail.gmail.com> <4E6A56D4.2030602@skype .net> <CABcZeBOdP6cAqBoiSV-Vdv1_EK3DfgnMamT3t3ccjDOMfELfBw@mail.gmail.com>
To: Eric Rescorla <ekr@rtfm.com>
X-Mailer: Apple Mail (2.1244.3)
Cc: Randell Jesup <randell-ietf@jesup.org>, Jonathan Lennox <jonathan@vidyo.com>, "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] AVPF [was: Encryption mandate (and offer/answer)]
X-BeenThere: rtcweb@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Real-Time Communication in WEB-browsers working group list <rtcweb.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/rtcweb>, <mailto:rtcweb-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/rtcweb>
List-Post: <mailto:rtcweb@ietf.org>
List-Help: <mailto:rtcweb-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/rtcweb>, <mailto:rtcweb-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sat, 10 Sep 2011 07:50:05 -0000

9 sep 2011 kl. 20:35 skrev Eric Rescorla:

> On Fri, Sep 9, 2011 at 11:11 AM, Matthew Kaufman
> <matthew.kaufman@skype.net>; wrote:
>> On 9/9/11 10:47 AM, Alan Johnston wrote:
>>> 
>>>   The default will be SRTP - this can be
>>> expressed in SDP without CapNeg.  Should the RTCWEB clients choose to
>>> instead negotiate RTP, then this could be done with a second SDP
>>> Offer/Answer exchange.
>> 
>> I believe you've just designed a downgrade vulnerability.
> 
> Unless I'm missing something, if you (a) support an insecure mode and (b) allow
> negotiation of insecure vs. secure, there's not really any way to
> avoid a downgrade
> issue; the attacker can always pretend not to support security and how do you
> know better? Obviously, it helps if you can negotiate the use or non-use of
> media security over a secure-ish signaling channel, but that doesn't reduce
> the threat from the signaling service.
> 
Have we solved the issues with a "secure-ish signaling channel" anywhere? I don't think we can assume that they exist in the architecture and build solutions based on that assumption. 

SIP/TLS end2end is still very hard to handle. Single hop is definitely protected assuming that we have a CA trust path that we trust, but mutli-hop is still very hard to assure as being "secure-ish" after all these years with SIP.

HTTPS is not an answer here either, especially not with the deployment of enterprise SSL proxys that fake a site certificate in order to be able to listen-in to the traffic.

/O