Chrome is including "use_srtp" extension for SCTP/DTLS data channels

[Raju]

Hi,

I noticed that Chrome is sending exact same DTLS Client Hello message for the following 3 cases:

1.DTLS-SRTP audio/video

2.DTLS-SRTP based data channels

3.SCTP-DTLS based data channels

For cases 1 and 2 it is understood that "use_srtp" is needed.

For case 3, I am not exactly sure why "use_srtp" extension is included? While as the application clearly wants SCTP/DTLS

based data channels only and no audio/video data channels are requested to be bundled along with same data channels.

Is this done in preparation of supporting bundling of audio, video and data channels on to a single DTLS association?

Is there a way to disable this? Especially when audio, video is not bundled along with data channels.

OR Chrome expects the peer to ignore the extension (per TLS/DTLS extension rules) and respond with Server Hello without the extension? 

I am using latest Chrome 34.

Thanks

Raju

 

[Justin Uberti]

The peer ought to ignore extensions it doesn't understand.

use_srtp is included even if no audio/video is currently bundled, because it might be added in the future, and we don't want to have to renegotiate at that time.

[Raju]

I agree with that approach. Thanks.