You'll have to get the key from the dtls stream, the srtp key is exchanged over the DTLS and applied to the session. You can see it in the rtp stack code.
On Tue, Sep 24, 2013 at 6:22 PM, Sam Russell <sam.h.russell@gmail.com> wrote:Your last email helped me disable DTLS from the client end, and I have the FreeSwitch DTLS key so I can decrypt the DTLS stream - it's just that wireshark now doesn't know what to do with the decrypted payload. Each decrypted DTLS packet starts with 0x80 and then often 0x00 like the RTP packets that come through in plaintext, but I can't make the RTP dissector work on the decrypted payload - should I just be turning off DTLS altogether so I can focus on the payload?On Wed, Sep 25, 2013 at 11:18 AM, Anthony Minessale <anthony.minessale@gmail.com> wrote:
I already told you about the constraints bit in the last email. =DOn Tue, Sep 24, 2013 at 6:05 PM, Sam Russell <sam.h.russell@gmail.com> wrote:
Thanks Anthony.For future reference, Chrome has DTLS disabled by default, so in JsSIP (check their source for how to clone your own full copy and hack on it) you just need to override this bit in js/gui.jsRTCConstraints: {"optional": [{'DtlsSrtpKeyAgreement': 'true'}]} // change true to falseAfter this, it only uses FreeSwitch's key, and you can then decrypt the handshake correctly in Wireshark - but it looks like Wireshark won't let you decode SRTP (it doesn't seem to handle the 0x80->RTCP muxing in the DTLS packets, and it won't let you choose SRTP as the inner protocol) - screenshot shows the output I get from wireshark 1.10.2 - http://i.imgur.com/NyVHAdy.pngAm I being a bit silly here, or does wireshark not yet have the capability to decode SRTP in DTLS?CheersSamOn Wed, Sep 25, 2013 at 3:07 AM, Anthony Minessale <anthony.minessale@gmail.com> wrote:They generate them iirc.There is a constraints field in the javascript that tells if you want to use dtls or not.Have you tried it with jssip?On Tue, Sep 24, 2013 at 5:00 AM, Sam Russell <sam.h.russell@gmail.com> wrote:
_________________________________________________________________________Hi,I've spent a few hours digging through captures and RFCs and I think I found where I'm getting caught - having the server key isn't enough - you need the client key (i.e. from your browser). I've got a couple of issues I'm tracking down with WebRTC support for FreeSwitch, does anybody know how to export private keys from Chrome/Firefox that they use for WebRTC? If I can get the browser private key AND the key from Freeswitch (dtls-srtp.key by the looks) then I can decrypt a DTLS stream and figure out what's going on.CheersSam
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AIM: anthm
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_________________________________________________________________________
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consulting@freeswitch.org
http://www.freeswitchsolutions.com
FreeSWITCH-powered IP PBX: The CudaTel Communication Server
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Official FreeSWITCH Sites
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http://wiki.freeswitch.org
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