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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am attempting to get optional SRTP to work based on rfc 8643. I have found that I can configure FreeSWITCH to allow for crypto in RTP/AVP, but I don’t seem to get it to work fully.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve used the configuration elements rtp_allow_crypto_in_avp and NDLB-allow-crypto-in-avp. Both give me the same results but neither fully works.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I found in the archives another person who experienced this same issue. It was in October of 2018 and is titled ‘Accepting an “optional” SRTP offer (crypto in RTP/AVP) and establishing SRTP’. In that case, he was using version 1.6.20.
From the responses, it seemed like in 1.8.2 it was possibly supposed to be working. I’m using 1.8.5 and I have tried it in 1.10.3 as well but they both seem to behave the same.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A recap of what is in the SDP offer and the SDP answer are as follows:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The endpoint is signaling optional SRTP according to rfc 8643 by sending a crypto token or a fingerprint in the SDP for a media descriptor that is signaled as RTP/AVP.<o:p></o:p></p>
<p class="MsoNormal"> <i>m=audio 58702 RTP/AVP 0 8 101<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>c=IN IP4 65.37.249.200<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>b=AS:64<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=rtpmap:0 PCMU/8000<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=rtpmap:8 PCMA/8000<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=rtpmap:101 telephone-event/8000<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=ptime:30<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=crypto:1 AES_256_CM_HMAC_SHA1_80 inline:8u1pUNOnFJUWKAa25GEtyFnHebV6AHrdpDgZ47nYBU6AtxlWiECv+RZPOSjW5g==<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=crypto:2 AES_CM_128_HMAC_SHA1_80 inline:q3iDyAquDcVye5MVFF4NR2Krli3PdmSwxMKGFK8D<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=setup:active<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=fingerprint:sha-1 5F:29:44:20:8A:CB:81:1C:DC:9B:B0:C6:4D:EB:01:C1:6B:B8:CE:8E<o:p></o:p></i></p>
<p class="MsoNormal"><i><o:p> </o:p></i></p>
<p class="MsoNormal">I can see in the console log that the initially prepared SDP answer contains an m-line with RTP/SAVP and it also contains the selected crypto attribute for the response.
<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><i>m=audio 25190 RTP/SAVP 0 101<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=rtpmap:0 PCMU/8000<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=rtpmap:101 telephone-event/8000<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=fmtp:101 0-16<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=ptime:30<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=sendrecv<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:.5in"><i>a=crypto:2 AES_CM_128_HMAC_SHA1_80 inline:JfypK+0Vu1y6WXx0B/hhARVcvzYmO0Tt3xRJGx3o</i><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yet before it is sent, it is changed to have the media channels disabled.<o:p></o:p></p>
<p class="MsoNormal"> <i>m=audio 0 RTP/AVP 19 <o:p></o:p></i></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">What else do I need to do to get this to work with optional encryption coming in the SDP-Offer?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Eugene Christensen<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><span style="font-size:8.0pt;font-family:"Arial",sans-serif;color:navy">CONFIDENTIALITY NOTICE.</span></b><span style="font-size:8.0pt;font-family:"Arial",sans-serif;color:navy"> This e-mail transmission, and any documents, files or
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<p class="MsoNormal"><o:p> </o:p></p>
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