[SR-Users] Regarding rtpengine dtls handling and fetching crypto keys

Richard Fuchs rfuchs at sipwise.com
Wed Jan 13 15:20:31 CET 2016

On 01/13/2016 02:37 AM, riko nir wrote:
> Hi, Thanks for the answer.
> Do you have any options for sending this keys to opensips somehow, by
> modifying the code in rtpengine and in opesips script file?

I don't know much about Opensips and so can't provide guidance about how 
to pass these values back to it.

> Also, I have another query. The SRTP keys that we are getting after the
> DTLS handshake is common for both audio and video streams for both RTP
> and RTCP?

Not necessarily. Multiple media streams normally use different ports and 
this will result in multiple DTLS sessions and thus different SRTP keys. 
The only exception is when BUNDLE is in use, but rtpengine will always 
break out of BUNDLE. As for RTCP, if RTP and RTCP use the same port on 
both sides (full rtcp-mux) then the keys will be the same. In all other 
cases, two DTLS sessions will be established and this will result in two 
sets of SRTP keys.


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