Re: [rtcweb] AVPF [was: Encryption mandate (and offer/answer)]

Dzonatas Sol <dzonatas@gmail.com> Fri, 09 September 2011 19:01 UTC

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Date: Fri, 09 Sep 2011 12:05:06 -0700
From: Dzonatas Sol <dzonatas@gmail.com>
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Subject: Re: [rtcweb] AVPF [was: Encryption mandate (and offer/answer)]
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On 09/09/2011 11:53 AM, Justin Uberti wrote:
>
>
> On Fri, Sep 9, 2011 at 2:35 PM, Eric Rescorla <ekr@rtfm.com 
> <mailto:ekr@rtfm.com>> wrote:
>
>     On Fri, Sep 9, 2011 at 11:11 AM, Matthew Kaufman
>     <matthew.kaufman@skype.net <mailto:matthew.kaufman@skype.net>> wrote:
>     > On 9/9/11 10:47 AM, Alan Johnston wrote:
>     >>
>     >>   The default will be SRTP - this can be
>     >> expressed in SDP without CapNeg.  Should the RTCWEB clients
>     choose to
>     >> instead negotiate RTP, then this could be done with a second SDP
>     >> Offer/Answer exchange.
>     >
>     > I believe you've just designed a downgrade vulnerability.
>
>     Unless I'm missing something, if you (a) support an insecure mode
>     and (b) allow
>     negotiation of insecure vs. secure, there's not really any way to
>     avoid a downgrade
>     issue; the attacker can always pretend not to support security and
>     how do you
>     know better? Obviously, it helps if you can negotiate the use or
>     non-use of
>     media security over a secure-ish signaling channel, but that
>     doesn't reduce
>     the threat from the signaling service.
>
>
> We can of course expose the encryption state to the application so 
> that it can decide if it wants to proceed with/warn about the 
> downgrade to plain old RTP.
>

That would be federalization then, not downgrade.


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