Re: [Sframe] SFrame signatures

Saúl Ibarra Corretgé <saghul@jitsi.org> Wed, 31 March 2021 09:28 UTC

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To: Justin Uberti <juberti=40google.com@dmarc.ietf.org>, Sframe@ietf.org
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Date: Wed, 31 Mar 2021 11:28:37 +0200
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Subject: Re: [Sframe] SFrame signatures
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On 18/03/2021 23:15, Justin Uberti wrote:
> In recent discussions regarding signatures for SFrame we have questioned 
> the usefulness of this feature and considered removing it. Upon looking 
> closer into the details here, we have also determined more work would be 
> required to properly specify it.
> 
> Given this, the authoring team would like to officially propose removing 
> the signature feature from the specification. If you are using SFrame 
> signatures in your application and disagree with this direction, please 
> let us know by the end of next week (Friday, March 26).
> 
> Justin
> 

Sorry for the delay responding.

We do currently use signatures on Jitsi. We started by signing every 
frame and compromising on the overhead.

The next step (currently in PR) was to sign multiple frames. 
Specifically, all keyframes, first frame from a new SSRC, and frame on 
which we needed to racthet are signed.

I'll say I'm not happy with the complexity this introduces, and I agree 
the attack vector is weird (a user in a conference is using the key of 
another user in the conference).

FWIW, Zoom deems this attack vector out of scope:

"""
Second, there are certain classes of attack and threats that we deem out 
of scope, including:In-meeting  impersonation  attacks:A  malicious  but 
  otherwise  authorized  meetingparticipant colluding with a malicious 
server can masquerade as another authorizedmeeting participant.
"""

https://raw.githubusercontent.com/zoom/zoom-e2e-whitepaper/master/zoom_e2e.pdf 
- Section 1.3.

I find myself agreeing here.

I see the authentication section was removed in draft -02 and section 
8.1 was added, nice to see that's explicit now.

We'll most likely be removing signatures for the time being.


Cheers,

-- 
Saúl