Subject: Re: [rtcweb] Sebastien Cubaud's non-ICE mechanism (Re: Summary of ICE discussion)
From: "Muthu Arul Mozhi Perumal (mperumal)" <[email-masked]>
To: "Harald Alvestrand" <[email-masked]>, <[email-masked]>
Date: Tue, 11 Oct 2011 17:35:07 +0530
List-Id: Real-Time Communication in WEB-browsers working group list <rtcweb.ietf.org>

|> - Assuming B receives these packets, it then sends 
|> via the signalling channel an information from the 
|> media path unknown from S (i.e. not accessible via JS).

A requirement hidden here is that B shouldn't alert the user till the entire consent verification is complete (otherwise B would have to buffer the media coming from the user). If B is a PSTN gateway this isn't going to be trivial to implement.

If we go down this path, I think we would end up reinventing ICE/ICE-Lite in a different form (which doesn't look worth the effort), so we should just make use of ICE.

Muthu

|-----Original Message-----
|From: [email-masked] [mailto:[email-masked]] On Behalf Of Harald Alvestrand
|Sent: Tuesday, October 11, 2011 2:20 AM
|To: [email-masked]
|Subject: [rtcweb] Sebastien Cubaud's non-ICE mechanism (Re: Summary of ICE discussion)
|
|Changing the subject to keep threads separate....
|
|On 10/09/2011 12:00 PM, [email-masked] wrote:
|> Hi there,
|>
|> Re Magnus's call for proposal (If anyone can find a solution that fulfill
|>   the security goals and have improved legacy interoperability people would
|> be interested in that solution. So far RTCP has been discarded as insufficient.)
|> on media consent verification, here is below a suggestion for the group:
|>
|> Basically, the idea, compared to Hadriel's RTCP proposal, relies on the use
|> of the signalling path instead of RTCP as a feedback channel for media
|> consent verification.
|>
|> Here are the steps I foresee before allowing the establishment of a media session:
|>
|> - Let's consider A (a RTC-Web compliant browser) connected to server S and
|> wishing to share real-time media with destination B (potentially a SIP
|> endpoint or a browser)
|> - A&  B learn via the signalling channel the triple @IP, transport proto and
|> associated listening port of the remote media
|> - A sends a few RTP packets to B (3 as in RFC 2833/4733 or more?).- This would
|>   allow the mechanism to resist against packet loss -. The format of such packets
|>   are to be discussed
|> - Assuming B receives these packets, it then sends via the signalling channel
|> an information from the media path unknown from S (i.e. not accessible via JS).
|> I propose to use the min of the sequence number of the RTP packets received
|> (which is random per RFC 3550)
|The sequence number is a 16-bit number, so there are 16 bits of
|randomness to play with here.
|An attack based on just returning a random number will succeed 1 out of
|65.536 times; if any of the 3 packets' sequence numbers are acceptable,
|it will succeed 1 out of 21.845 times.
|
|A browser can reasonably limit the number of attempts per second (either
|overall or per-script); multiple browsers will not be able to coordinate
|on any such limit.
|
|Is this defense strong enough to warrant considering this further?
|
|> - A receives via S this info granting B's consent to receiving media from A
|> - A now can start sending media to B
|>
|> When B uses SIP as its signalling channel, Step 4 would probably require a
|> SDP extension to convey this info, as well as possibly extended H.248/Diameter
|>   informations would be required in a decoupled sig./media architecture.
|> Of course, a solution avoiding extensions would be more than welcome.
|>
|> The benefit of this mechanism largely relies on the assumption that the
|> transmission of information from the media termination of the destination
|> to its associated signalling channel is less costly than implementing ICE connectivity
|> checks. Which is still to be checked.
|>
|> This mechanism provides basic media consent verification and if it turns out
|> that it provides less security properties than ICE or other drawbacks (e.g.
|> increasing media session establishment delay, issues with the few initial RTP
|> packets,..), it could be seen as a fallback media consent verification
|> when ICE is not implemented at each end of media terminations.
|>
|> Looking forward to hearing feedbacks from the group on this.
|>
|> Cheers
|> Sebastien
|>
|> -----Message d'origine-----
|> De : [email-masked] [mailto:[email-masked]] De la part de Magnus Westerlund
|> Envoyé : mardi 4 octobre 2011 16:33
|> À : [email-masked]
|> Objet : [rtcweb] Summary of ICE discussion
|>
|> WG,
|>
|> I have bellow tired to summarize the result of the ICE discussion. This
|> is intended as furthering this discussion and form a basis for going
|> forward in the consensus process. I do expect people that disagree with
|> my summary of the discussion to speak up.
|>
|> Major requirements
|>
|> - Need for data transmission consent for protocols using UDP as the
|> traffic receiver needs to consent to receiving the data
|>
|> - Perform NAT and FW traversal when ever needed
|>
|> - Support IPv4 to IPv6 transition
|>
|> Desired behavior:
|>
|> - Be interoperable with deployed legacy systems as SIP Trunk, PSTN
|> gateways, VoIP phones.
|>
|> WG chairs conclusion of discussion so far:
|>
|> - ICE is so far the only solution that provides the security goals and
|> have any legacy deployment.
|>
|> - ICE usage will require that STUN connectivity MUST have succeeded
|> prior to any data transmission to fulfill security goals.
|>
|>    * The Browser will enforce this requirement to prevent being an attack
|> vector in all cases.
|>
|> - If anyone can find a solution that fulfill the security goals and have
|> improved legacy interoperability people would be interested in that
|> solution. So far RTCP has been discarded as insufficient.
|>
|> - Media Gateway can support a reduced functionality set from Full ICE
|>
|> Cheers
|>
|> Magnus Westerlund
|> as WG chair
|>
|> ----------------------------------------------------------------------
|> Multimedia Technologies, Ericsson Research EAB/TVM
|> ----------------------------------------------------------------------
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|> SE-164 80 Stockholm, Sweden| mailto: [email-masked]
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