TLS, SRTP and SRTCP

Asterisk Asterisk Support
1

Hi,

I have an Asterisk 12 installation talking to an Avaya over TLS but I need to secure the audio streams using SRTP.

The SDP in the INVITE from the Avaya contains:
a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:a84nzjof8LyBy0xcGEi1fGkkEv8RCLG5E9IcofL9 UNENCRYPTED_SRTCP

And the Asterisk logging shows:
Found RTP audio format 8
Found RTP audio format 18
Found RTP audio format 127
Found audio description format PCMA for ID 8
Found audio description format G729 for ID 18
Found audio description format telephone-event for ID 127
[Mar 21 17:39:18] WARNING[2236][C-00000035]: sdp_srtp.c:240 ast_sdp_crypto_process: Unsupported crypto parameters: UNENCRYPTED_SRTCP
[Mar 21 17:39:18] WARNING[2236][C-00000035]: chan_sip.c:10620 process_sdp: Rejecting secure audio stream without encryption details: audio 2076 RTP/SAVP 8 18 127

<— Reliably Transmitting (no NAT) to xxx.xxx.xxx.xxx:5060 —>
SIP/2.0 488 Not acceptable here

Now Asterisk is only reporting warnings but the call doesn’t get set up. Is lack of support for UNENCRYPTED_SRTCP the problem or is there something more fundamental wrong?

Thanks in advance,
Regards,
AlanR.

2

Lack of support is the problem. Asterisk is unable to establish an encryption key but has been told it must use one.

Actually, that rather sounds like a statement that the RTP won’t be encrypted!