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Failing to get SRTP to work

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Ben Rush
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Failing to get SRTP to work

Ben Rush
I've looked at the following: 

https://lists.freedesktop.org/archives/gstreamer-bugs/2017-August/204646.html 
https://stackoverflow.com/questions/7669240/webcam-streaming-using-gstreamer-over-udp 

...but for whatever reason, I still cannot get SRTP to work at the command line (Windows).  What I mean by that is running both a "server" and a "client" and having them communicate with each other over SRTP. The most insightful comment was: 

 "You have to connect to the "request-key" signal and return appropriate
caps there, or make sure to set complete caps on the stream via udpsrc. Your caps are missing the "roc" field at least."

...in the last link above. But, I'm doing what's suggested there (I believe, anyway). Here are my commands: 

 Server == gst-launch-1.0 videotestsrc ! videoconvert ! openh264enc ! rtph264pay ! application/x-rtp, payload=(int)96 ! srtpenc key=987654321001234567890123456789012345678901234567890123456789 rtp-cipher=aes-128-icm rtp-auth=hmac-sha1-80 rtcp-cipher=aes-128-icm rtcp-auth=hmac-sha1-80 ! udpsink host=127.0.0.1 port=5000

Client == gst-launch-1.0 udpsrc port=5000 caps="application/x-srtp, payload=(int)96, srtp-key=(buffer)987654321001234567890123456789012345678901234567890123456789, srtp-cipher=(string)aes-128-icm, srtp-auth=(string)hmac-sha1-80, srtcp-cipher=(string)aes-128-icm, srtcp-auth=(string)hmac-sha1-80, roc=(uint)0" ! srtpdec ! rtph264depay ! h264parse ! openh264dec ! videoconvert ! autovideosink

To test, I fire up the "server" first and it spins up and waits. That part appears to be correct. However, when running the "client", I get a spew of: 

0:00:02.197235000 23116 000001FF981D7040 WARN                 srtpdec gstsrtpdec.c:992:request_key_with_signal:<srtpdec0> Could not get caps for stream with SSRC 1451949075

Ok. So, to do some digging. The code is here:   https://github.com/agx/gst-plugins-bad/blob/master/ext/srtp/gstsrtpdec.c. The comment here: https://github.com/agx/gst-plugins-bad/blob/74bcc835aa7d74e83e69eafe83869c1be72195a5/ext/srtp/gstsrtpdec.c#L286 seems to indicate maybe the plugin is unable to determine the keys and cipher information it needs. This seems to jive with the comment I mentioned earlier (that I need to then put them as caps on the udpsrc, therefore) ... but I'm doing that. Do you spot anything wrong with my caps? I assume the mechanism is srtpdec is signaling to the pipeline to give to it the parameters it needs, but it's not getting a response or getting something invalid. 

Thanks in advance. 

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Ben Rush
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Re: Failing to get SRTP to work

Ben Rush
I seemed to solve it myself, I had to add the ssrc key/value pair. Here are the commands that do work for me now: 

Server: gst-launch-1.0 videotestsrc ! videoconvert ! openh264enc ! rtph264pay ! application/x-rtp, payload=(int)96, ssrc=(uint)1356955624 ! srtpenc key=987654321001234567890123456789012345678901234567890123456789 rtp-cipher=aes-128-icm rtp-auth=hmac-sha1-80 rtcp-cipher=aes-128-icm rtcp-auth=hmac-sha1-80 ! udpsink host=127.0.0.1 port=5000

Client: gst-launch-1.0 udpsrc port=5000 caps="application/x-srtp, encoding-name=H264, payload=(int)96, ssrc=(uint)1356955624, srtp-key=(buffer)987654321001234567890123456789012345678901234567890123456789, srtp-cipher=(string)aes-128-icm, srtp-auth=(string)hmac-sha1-80, srtcp-cipher=(string)aes-128-icm, srtcp-auth=(string)hmac-sha1-80, roc=(uint)0" ! srtpdec ! rtph264depay ! h264parse ! openh264dec ! videoconvert ! autovideosink

I'm not sure why setting the synchronization source ID needs to be explicit and not something negotiated (probably me not understanding some internal very well), but that did it for me. 

Sorry for the spamming. 

On Wed, Sep 25, 2019 at 3:00 PM Ben Rush <[hidden email]> wrote:
I've looked at the following: 

https://lists.freedesktop.org/archives/gstreamer-bugs/2017-August/204646.html 
https://stackoverflow.com/questions/7669240/webcam-streaming-using-gstreamer-over-udp 

...but for whatever reason, I still cannot get SRTP to work at the command line (Windows).  What I mean by that is running both a "server" and a "client" and having them communicate with each other over SRTP. The most insightful comment was: 

 "You have to connect to the "request-key" signal and return appropriate
caps there, or make sure to set complete caps on the stream via udpsrc. Your caps are missing the "roc" field at least."

...in the last link above. But, I'm doing what's suggested there (I believe, anyway). Here are my commands: 

 Server == gst-launch-1.0 videotestsrc ! videoconvert ! openh264enc ! rtph264pay ! application/x-rtp, payload=(int)96 ! srtpenc key=987654321001234567890123456789012345678901234567890123456789 rtp-cipher=aes-128-icm rtp-auth=hmac-sha1-80 rtcp-cipher=aes-128-icm rtcp-auth=hmac-sha1-80 ! udpsink host=127.0.0.1 port=5000

Client == gst-launch-1.0 udpsrc port=5000 caps="application/x-srtp, payload=(int)96, srtp-key=(buffer)987654321001234567890123456789012345678901234567890123456789, srtp-cipher=(string)aes-128-icm, srtp-auth=(string)hmac-sha1-80, srtcp-cipher=(string)aes-128-icm, srtcp-auth=(string)hmac-sha1-80, roc=(uint)0" ! srtpdec ! rtph264depay ! h264parse ! openh264dec ! videoconvert ! autovideosink

To test, I fire up the "server" first and it spins up and waits. That part appears to be correct. However, when running the "client", I get a spew of: 

0:00:02.197235000 23116 000001FF981D7040 WARN                 srtpdec gstsrtpdec.c:992:request_key_with_signal:<srtpdec0> Could not get caps for stream with SSRC 1451949075

Ok. So, to do some digging. The code is here:   https://github.com/agx/gst-plugins-bad/blob/master/ext/srtp/gstsrtpdec.c. The comment here: https://github.com/agx/gst-plugins-bad/blob/74bcc835aa7d74e83e69eafe83869c1be72195a5/ext/srtp/gstsrtpdec.c#L286 seems to indicate maybe the plugin is unable to determine the keys and cipher information it needs. This seems to jive with the comment I mentioned earlier (that I need to then put them as caps on the udpsrc, therefore) ... but I'm doing that. Do you spot anything wrong with my caps? I assume the mechanism is srtpdec is signaling to the pipeline to give to it the parameters it needs, but it's not getting a response or getting something invalid. 

Thanks in advance. 

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