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Re: [dispatch] Fwd: I-D Action: draft-johnston-dispatch-osrtp-00.txt

Richard Barnes <rlb@ipv.sx> Wed, 08 July 2015 20:25 UTC

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Date: Wed, 08 Jul 2015 16:25:11 -0400
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From: Richard Barnes <rlb@ipv.sx>
To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [dispatch] Fwd: I-D Action: draft-johnston-dispatch-osrtp-00.txt
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On Wed, Jul 8, 2015 at 3:50 PM, Martin Thomson <martin.thomson@gmail.com> wrote:
> On 8 July 2015 at 11:42, Alan Johnston <alan.b.johnston@gmail.com> wrote:
>> I was on the fence about this one.  Agree that it shouldn't happen for
>> DTLS-SRTP or ZRTP, but I could imagine it happening for certain MIKEY modes.
>> Should that really fail the whole session?
>
> At the point that you have established that both peers support a
> common baseline, accepting downgrade from that baseline removes any of
> the benefit that an opportunistic upgrade provided.  An attacker that
> can't attack your signaling now has a chance to downgrade you.

+1

The idea is "opportunistic" in the sense of "if both peers can
negotiate in signaling", not in the sense of "keep going if the
security fails".


> I've no good information on what MIKEY mode might fail and how, but
> that seems like a problem you could address specifically without
> weakening other options.
>
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