4.1 Peer Clients Require Encryption

Alice sends Bob an INVITE request for an audio call requesting encryption by including the a=encryption:required attribute and the SDP field k= with a suitable key.

Bob accepts the call with a 200 OK with the a=encryption:required attribute and the k= field.

Alice sends an ACK.

Alice and Bob start sending media encrypted with the keys negotiated using the k= field.

Audio call requesting encryption

Figure 1: Audio call requesting encryption

The following is an example of SDP signaling in an SIP INVITE request that is sent across the wire.

 v=0
 o=- 0 0 IN IP4 11.22.33.44
 s=session
 c=IN IP4 11.22.33.44
 b=CT:1000
 t=0 0
 m=audio 5050 RTP/AVP 97 111 112 6 0 8 4 5 3 101
 k=base64: Y6UN8SAFnqNTI61uN+1II3dqRk0spxbtqfuv5EYSYSM
 a=rtpmap:97 red/8000
 a=rtpmap:111 SIREN/16000
 a=fmtp:111 bitrate=16000
 a=rtpmap:112 G7221/16000
 a=fmtp:112 bitrate=24000
 a=rtpmap:6 DVI4/16000
 a=rtpmap:0 PCMU/8000
 a=rtpmap:8 PCMA/8000
 a=rtpmap:4 G723/8000
 a=rtpmap:5 DVI4/8000
 a=rtpmap:3 GSM/8000
 a=rtpmap:101 telephone-event/8000
 a=fmtp:101 0-16
 a=encryption:required
 m=video 5036 RTP/AVP 34 31
 k=base64: Y6UN8SAFnqNTI61uN+1II3dqRk0spxbtqfuv5EYSYSM
 a=rtpmap:34 H263/90000
 a=rtpmap:31 H261/90000
 a=encryption:required
  
  

The following is an example of SDP signaling in the 200 OK response that is received across the wire in response to the INVITE.

  
  
 v=0
 o=- 0 0 IN IP4 11.22.33.55
 s=session
 c=IN IP4 11.22.33.55
 b=CT:1000
 t=0 0
 m=audio 5050 RTP/AVP 97 111 112 6 0 8 4 5 3 101
 k=base64: h6KmqIeIFj3rz4iiMAsYQju5EEitwAiveVu7RuHhev8
 a=rtpmap:97 red/8000
 a=rtpmap:111 SIREN/16000
 a=fmtp:111 bitrate=16000
 a=rtpmap:112 G7221/16000
 a=fmtp:112 bitrate=24000
 a=rtpmap:6 DVI4/16000
 a=rtpmap:0 PCMU/8000
 a=rtpmap:8 PCMA/8000
 a=rtpmap:4 G723/8000
 a=rtpmap:5 DVI4/8000
 a=rtpmap:3 GSM/8000
 a=rtpmap:101 telephone-event/8000
 a=fmtp:101 0-16
 a=encryption:required
 m=video 5036 RTP/AVP 34 31
 k=base64: h6KmqIeIFj3rz4iiMAsYQju5EEitwAiveVu7RuHhev8
 a=rtpmap:34 H263/90000
 a=rtpmap:31 H261/90000
 a=encryption:required