[whatwg] Reusing SRTP (Re: Peer-to-peer communication, video conferencing, and related topics (2))

Harald Alvestrand harald at alvestrand.no
Tue Mar 29 04:41:44 PDT 2011

On 03/29/11 03:00, Ian Hickson wrote:
> On Wed, 23 Mar 2011, Harald Alvestrand wrote:
>> >
>> >  Is there really an advantage to not using SRTP and reusing the RTP
>> >  format for the data messages?
> Could you elaborate on how (S)RTP would be used for this? I'm all in
> favour of defering as much of this to existing protocols as possible, but
> RTP seemed like massive overkill for sending game status packets.
If "data" was defined as an RTP codec ("application/packets?"), SRTP 
could be applied to the packets.
It would impose a 12-byte header in front of the packet and the 
recommended authentication tag at the end, but would ensure that we 
could use exactly the same procedure for key exchange, multiplexing of 
multiple data streams on the same channel using SSRC, and procedures for 
identifying the stream in SDP (if we continue to use SDP) - I believe 
SDP implicitly assumes that all the streams it describes are RTP streams.

I've been told that defining RTP packetization formats for a codec needs 
to be done carefully, so I don't think this is a full specification, but 
it seems that the overhead of doing so is on the same order of magnitude 
as the currently proposed solution, and the security properties then 
become very similar to the properties for media streams.

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