Re: [rtcweb] draft-ietf-rtcweb-rtp-usage-12 Client-to-Mixer Audio Level

Martin Thomson <martin.thomson@gmail.com> Wed, 05 March 2014 16:10 UTC

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Date: Wed, 5 Mar 2014 16:09:57 +0000
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From: Martin Thomson <martin.thomson@gmail.com>
To: Justin Uberti <juberti@google.com>
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Cc: "Cullen Jennings \(fluffy\)" <fluffy@cisco.com>, "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] draft-ietf-rtcweb-rtp-usage-12 Client-to-Mixer Audio Level
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On 5 March 2014 14:40, Justin Uberti <juberti@google.com> wrote:
> Agree with Cullen (and FWIW the SRTP encryption uses keys vended from the
> DTLS master secret, so I think even if you are able to crack the SRTP crypto
> it would not be trivial to go backwards up to the DTLS key material)

Yes.  DTLS-SRTP extracts keys, so working backwards to the master
secret would mean that not only have you cracked SRTP, but that you
can also produce a HMAC preimage at will.