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

"Muthu Arul Mozhi Perumal (mperumal)" <> Wed, 09 May 2012 07:35 UTC

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Date: Wed, 09 May 2012 13:04:56 +0530
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Thread-Topic: [rtcweb] Consent freshness - revisiting the RTCP option
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From: "Muthu Arul Mozhi Perumal (mperumal)" <>
To: Harald Alvestrand <>, Eric Rescorla <>
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Subject: Re: [rtcweb] Consent freshness - revisiting the RTCP option
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More reasons why RTCP may not be suitable for consent freshness:
1. RTCP (as described in RFC3550) is receiver based, so the browser
can't explicitly request for consent. If consent freshness fails (for
e.g, RTCP packets temporarily lost because of network flapping), the
browser would have to wait for the peer to send RTCP before it can start
transmitting media. Worst, if the peer isn't an active sender it may not
send any RTCP RR until it receives media. It could send a bare minimum
RTCP RR (an RR with RC=0 and SDES with CNAME), but that has zero

2. There are still some endpoints that don't send / pay attention to

For these cases an intermediary like an SBC would have to manufacture
them. Manufacturing them for just consent freshness would be expensive
compared to generating STUN request/response.


|-----Original Message-----
|From: [] On
Behalf Of Harald Alvestrand
|Sent: Wednesday, May 09, 2012 12:26 PM
|To: Eric Rescorla
|Subject: Re: [rtcweb] Consent freshness - revisiting the RTCP option
|On 05/08/2012 11:59 PM, Eric Rescorla wrote:
|> On Tue, May 8, 2012 at 2:54 PM, Harald
Alvestrand<>  wrote:
|>> Just because I realized I didnt understand something, I ask.....
|>> We rejected RTCP RR as a consent freshness mechanism because RR is
|>> to fake.
|>> But - now we have SRTP as mandatory-to-use, which means that all
|>> 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
|> 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.
|rtcweb mailing list