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

Martin Thomson <martin.thomson@gmail.com> Wed, 08 July 2015 19:50 UTC

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Date: Wed, 08 Jul 2015 12:50:20 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: Alan Johnston <alan.b.johnston@gmail.com>
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Cc: DISPATCH <dispatch@ietf.org>
Subject: Re: [dispatch] Fwd: I-D Action: draft-johnston-dispatch-osrtp-00.txt
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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.

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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