Re: [rtcweb] SDP Security Descriptions (RFC 4568) and RTCWeb

[Dan Wing <[e-mail]>]

On Apr 25, 2013, at 9:39 AM, Alan Johnston <[e-mail]> wrote:

> I'm not a fan of SDES. However, I've come to believe that we need it for two reasons. 
> 
> 1. There is a backwards compatibility reason. There are deployed systems of SRTP that use SDES or a key agreement that easily maps to it. Just as we allowed G.711 for these systems, it seems reasonable to allow SDES as well. When combined with ICE Lite in a media gateway, this is a scalable interop approach. 

Interworking at scale can be accomplished without SDES on WEBRTC, as I explained at IETF83 in slides 27-35 of http://www.ietf.org/proceedings/83/slides/slides-83-rtcweb-3.pdf.

> 2. We need it or something like it for API reasons. There are cases where the JavaScript needs to tell the browser what SRTP key to use.

DTLS-SRTP with EKT can also perform that function, and does it without disclosing the SRTP key to all the SIP proxies and all the web servers on the signaling path.

> Since JSEP uses SDP for this API surface, SDES works for this. Obviously it is a bad idea to send this key over unsecured channels, but this is separate from this API issue. 
> 
> And just to be clear, browser to browser should use DTLS-SRTP, and only thus mode should be considered "secure" using whatever user interface a browser chooses. 

But is there a secure mechanism to differentiate browser-to-browser calls from browser-to-non-browser calls, so we don't have to worry over SDES downgrade attacks?  And for the use-cases where JavaScript has to set the key, those will often be browser-to-browser calls, meaning that we will have to support browser-to-browser SDES, contrary to your desire that browser-to-browser use DTLS-SRTP?  DTLS-SRTP with EKT permits the application to set the SRTP key, and more securely than SDES.

-d


> 
> - Alan -
> 
> 
> 
> On Apr 25, 2013, at 11:57 AM, Cullen Jennings <[e-mail]> wrote:
> 
>> 
>> The working groups committed some time ago to have a further discussion on whether SDP Security Descriptions (RFC 4568 aka SDES) would be usable as a keying method for WebRTC.  As we prepare for that discussion, we'd like to have expressions of interest or support for that approach which indicate the general outlines of support proposed.  If you wish to make such an expression of support, please send it to the chairs or the list.
>> 
>> Cullen, Magnus, & Ted <The Chairs>
>> 
>> 
>> _______________________________________________
>> rtcweb mailing list
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/rtcweb
> _______________________________________________
> rtcweb mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/rtcweb