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Re: [rtcweb] SDP Security Descriptions (RFC 4568) and RTCWeb

Dan Wing <dwing@cisco.com> Fri, 26 April 2013 13:57 UTC

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From: Dan Wing <dwing@cisco.com>
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Date: Fri, 26 Apr 2013 06:56:57 -0700
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To: Harald Alvestrand <harald@alvestrand.no>
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Subject: Re: [rtcweb] SDP Security Descriptions (RFC 4568) and RTCWeb
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On Apr 26, 2013, at 6:33 AM, Harald Alvestrand <harald@alvestrand.no> wrote:

> On 04/26/2013 03:16 PM, Tim Panton wrote:
>> 
>> On 26 Apr 2013, at 12:37, Iñaki Baz Castillo wrote:
>> 
>>> Such a solution requires a very expensive gateway. Good for vendors but bad for all the rest.
>>> 
>> 
>> I don't understand why the DTLS gateway would be so expensive. It is _exactly_ the same
>> (conceptually) as the ICE processing - you filter off a few UDP packets from the stream, do some
>> stuff, send replies then once you are happy you punt some dynamic settings back up to the (s)rtp
>> layer.
> 
> So you're saying that the gateway doesn't have to decrypt and re-encrypt the packets?

Correct - the gateway does not have to decrypt and re-encrypt the SRTP packets.  The gateway only has to interwork the signaling between SDES and DTLS-SRTP-EKT.  Such signaling interworking is necessary when the call is initially set up and when the SRTP key is changed (e.g., a new person joins a call using their own key, or the SRTP key is exhausted [pretty unlikely, even with video]).  This was summarized in http://www.ietf.org/proceedings/83/slides/slides-83-rtcweb-3.pdf


> 
> I think EKT may be a problem, as Inaki pointed out, but I have less qualms about supporting DTLS and making it optional to use EKT on some calls than I have about mandating support for SDES.

-d


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