signalling rollover count for srtp

[Bryan]

For group keying, it would be helpful if there were some way to signal SRTP rollover count to new receivers.  

Is rollover count signalling possible (or planned) in Chrome's implementation of WebRTC ?

from http://tools.ietf.org/html/rfc3711#section-3.3.1

 The index estimate is based on the receiver's locally maintained ROC
   and s_l values.  At the setup of the session, the ROC MUST be set to
   zero.  Receivers joining an on-going session MUST be given the
   current ROC value using out-of-band signaling such as key-management
   signaling.  Furthermore, the receiver SHALL initialize s_l to the RTP
   sequence number (SEQ) of the first observed SRTP packet (unless the
   initial value is provided by out of band signaling such as key
   management).

[Justin Uberti]

This is not currently supported or planned. With AES-NI, the cost of crypto ops is low enough that a middlebox can easily recrypt for each receiver. Also, this is the only way that data channel fanout (using DTLS) can work.

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