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

Justin Uberti <juberti@google.com> Fri, 09 September 2011 21:27 UTC

Return-Path: <juberti@google.com>
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 D03C721F88B7 for <rtcweb@ietfa.amsl.com>; Fri, 9 Sep 2011 14:27:52 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -104.849
X-Spam-Level:
X-Spam-Status: No, score=-104.849 tagged_above=-999 required=5 tests=[AWL=-0.539, BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_MED=-4, SARE_HTML_USL_OBFU=1.666, USER_IN_WHITELIST=-100]
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 mMCBesaFMHj9 for <rtcweb@ietfa.amsl.com>; Fri, 9 Sep 2011 14:27:52 -0700 (PDT)
Received: from smtp-out.google.com (smtp-out.google.com [216.239.44.51]) by ietfa.amsl.com (Postfix) with ESMTP id E6BAD21F8715 for <rtcweb@ietf.org>; Fri, 9 Sep 2011 14:27:51 -0700 (PDT)
Received: from wpaz33.hot.corp.google.com (wpaz33.hot.corp.google.com [172.24.198.97]) by smtp-out.google.com with ESMTP id p89LTh76019217 for <rtcweb@ietf.org>; Fri, 9 Sep 2011 14:29:43 -0700
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=google.com; s=beta; t=1315603783; bh=amXv2hUe/7IGFVqK1otEf6hSCbQ=; h=MIME-Version:In-Reply-To:References:From:Date:Message-ID:Subject: To:Cc:Content-Type; b=Q/UZN4WI5V3ZOIbwfhtVXZC/00jSt39Y85Pm1W4QLpHBOjjFZF0C3WDyaE5frfBG9 9rQny13bBGXeltJnB9e6g==
DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=dkim-signature:mime-version:in-reply-to:references:from:date: message-id:subject:to:cc:content-type:x-system-of-record; b=sJOVTSiHd+v8DVba/tQu9zHHptXekhSt4Gn4BPBkdNdwGd2KjdXGYRn6shWsBq3uL yeEaTlPU7z51eJs5tcMfw==
Received: from gya6 (gya6.prod.google.com [10.243.49.6]) by wpaz33.hot.corp.google.com with ESMTP id p89LTeKB020716 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for <rtcweb@ietf.org>; Fri, 9 Sep 2011 14:29:42 -0700
Received: by gya6 with SMTP id 6so1535727gya.0 for <rtcweb@ietf.org>; Fri, 09 Sep 2011 14:29:42 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; bh=AbEss+Bd7EiinDX6ByvXjnIOro1YE+2LwNikSDTxbxA=; b=frXkjkvPkAG6FqzKqO0o6TKCIyNLqF5hn3/4Exqj1UJlMAraP2KCsxFs4rMxLOz1o4 SFOOZwC8v7Qc7AfyWmdQ==
Received: by 10.231.41.69 with SMTP id n5mr2954586ibe.92.1315603782336; Fri, 09 Sep 2011 14:29:42 -0700 (PDT)
Received: by 10.231.41.69 with SMTP id n5mr2954578ibe.92.1315603782187; Fri, 09 Sep 2011 14:29:42 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.231.36.10 with HTTP; Fri, 9 Sep 2011 14:29:22 -0700 (PDT)
In-Reply-To: <4E6A81EC.3080002@jesup.org>
References: <A444A0F8084434499206E78C106220CA0B00FDB08B@MCHP058A.global-ad.net> <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> <CAKhHsXFdU1ZaKQF8hbsOxwTS-_RfmFqQhgzGe=K4mRp+wz+_nQ@mail.gmail.com> <4E6A81EC.3080002@jesup.org>
From: Justin Uberti <juberti@google.com>
Date: Fri, 09 Sep 2011 17:29:22 -0400
Message-ID: <CAOJ7v-369529AyNsuavbBN7VgLgZXu8LjUYH-DC8-7zdo+yhoA@mail.gmail.com>
To: Randell Jesup <randell-ietf@jesup.org>
Content-Type: multipart/alternative; boundary="0015177407d41a3b4e04ac88e052"
X-System-Of-Record: true
Cc: 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: Fri, 09 Sep 2011 21:27:52 -0000

On Fri, Sep 9, 2011 at 5:15 PM, Randell Jesup <randell-ietf@jesup.org>wrote:

> On 9/9/2011 3:23 PM, Alan Johnston wrote:
>
>> Ekr is correct.  If we allow RTP, which I think is a mistake, then
>> there is always a downgrade attack.
>>
>
> Yes, that's true.  The same issue was involved in the best-effort-srtp
> draft, which unfortunately
> was dropped because CapNeg would "solve" it.  (For historical note, it's
> still not "solved"
> because CapNeg support is >>>> more complex than best-effort-srtp and not
> generally deployed,
> and I doubt ever will be ala SDPng (though I'm not close to status on
> CapNeg.)
>
> Hmmm.  A real downgrade attack requires that the signalling be compromised.
>  I wonder if there
> are characteristics of a webrtc transaction that could help avoid this sort
> of attack (for example,
> a secondary way out-of-scope here for the app to know ahead of time if the
> target will need to
> be downgraded).  Or some way for the service to vouch for the downgrade
> (i.e. wasn't a MITM).
> You have to trust the service, but in this case you're doing so to this
> degree anyways.
>
>
>  My point was that if we must support insecure media, we could avoid
>> the complexity of CapNeg by not requiring a single pass non-secure
>> media negotiation.
>>
>
> There is another option.  I talked about services that wanted to support
> PSTN  could decide if they
> were willing to support a downgrade.  The application could know it's
> calling a PSTN gateway and
> if it does know that, avoid a media gateway by not offering encrypted
> media.
>
> I see a significant use-case for some services will be calling PSTN numbers
> and services, much
> as it is now for VoIP.
> Yes, a bunch of new non-legacy services wouldn't use/want it.  But the app
> for a PSTN-using service
> could specifically allow it.
>
> So the question comes down to what's the advantage to using unencrypted
> RTP?
> 1) No media gateway needed.  This is the big one.  Saves on $$$, saves on
> delay (sometimes a lot),
>    may save on complexity in a PBX type of situation.
>    But is there an issue due to ICE requirements?  If those can't be turned
> off safely too, that kills this
>    whole discussion I think.
> 2) Debug/etc tools work better with RTP.  Not important.
> 3) May simplify/improve some E911 cases.  Might be important; likely not.


In Quebec City, the mic discussion also noted a use case for enterprises
that want to log communications.

Regarding #1, the ability to avoid media gateways for "contemporary devices"
has been a design requirement from the start. I think we need to have a
clear understanding that this requirement creates serious, unavoidable
problems before jettisoning it.




> So, effectively it comes down to "is advantage 1 worth the
> complexity/risk?"  Anyone want to defend that
> case?
>
>  - Alan -
>>
>> On Fri, Sep 9, 2011 at 1:35 PM, Eric Rescorla<ekr@rtfm.com>  wrote:
>>
>>> 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.
>>>
>>> Best,
>>> -Ekr
>>>
>>>
> --
> Randell Jesup
> randell-ietf@jesup.org
>
>
> ______________________________**_________________
> rtcweb mailing list
> rtcweb@ietf.org
> https://www.ietf.org/mailman/**listinfo/rtcweb<https://www.ietf.org/mailman/listinfo/rtcweb>
>