Re: [rtcweb] Consent freshness - revisiting the RTCP option

Harald Alvestrand <harald@alvestrand.no> Wed, 09 May 2012 06:56 UTC

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Date: Wed, 09 May 2012 08:56:12 +0200
From: Harald Alvestrand <harald@alvestrand.no>
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To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [rtcweb] Consent freshness - revisiting the RTCP option
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On 05/08/2012 11:59 PM, Eric Rescorla wrote:
> On Tue, May 8, 2012 at 2:54 PM, Harald Alvestrand<harald@alvestrand.no>  wrote:
>> Just because I realized I didnt understand something, I ask.....
>>
>> We rejected RTCP RR as a consent freshness mechanism because RR is trivial
>> to fake.
>> But - now we have SRTP as mandatory-to-use, which means that all RTCP RRs
>> are integrity protected, origin authenticated and replay protected (do I
>> have that right?).
>>
>> What is the reason why this is not sufficient protection to use RTCP RR as a
>> consent freshness mechanism?
> This isn't a complete analysis, but if you are using SDES for key management,
> then the site knows the SRTCP keys, so I don't *think* SRTCP is buying you
> much. I haven't thought through this completely though, so maybe there is
> still some additional value.
Ah - had forgotten that the attacker is assumed to observe the 
signalling path. Thanks.