Re: [secdir] [xmpp] SecDir review of draft-ietf-xmpp-3920bis-17

Matthew Wild <mwild1@gmail.com> Wed, 03 November 2010 18:10 UTC

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From: Matthew Wild <mwild1@gmail.com>
Date: Wed, 3 Nov 2010 18:10:25 +0000
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To: Peter Saint-Andre <stpeter@stpeter.im>
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Cc: Security Area Directorate <secdir@ietf.org>, "draft-ietf-xmpp-3920bis.all@tools.ietf.org" <draft-ietf-xmpp-3920bis.all@tools.ietf.org>, Kurt Zeilenga <Kurt.Zeilenga@isode.com>, XMPP Working Group <xmpp@ietf.org>, The IESG <iesg@ietf.org>
Subject: Re: [secdir] [xmpp] SecDir review of draft-ietf-xmpp-3920bis-17
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On 3 November 2010 17:31, Peter Saint-Andre <stpeter@stpeter.im>; wrote:
>

>      as described under Section 13.7.2.1 (however, the lack of channel
>      binding in the PLAIN mechanism implies that even authenticated TLS
>      cannot fully protect the SASL negotiation and subsequent
>      communications when PLAIN is used).
>

I'm no expert on this, but is this text technically true? I thought
channel binding would only be beneficial where there is not full TLS
authentication.

I'm not going to weigh in on the to-MTI/to-not-MTI issue... it's not
going to affect anything either way. There are deployment scenarios
where PLAIN is necessary, and as far as I'm aware it is quite safe
with full TLS verification/authentication. I think Kurt is mainly
arguing that in practice TLS is rarely fully verified. However this is
a deployment issue, and has no bearing on the protocol - though were
we to MTI for interop reasons we should of course strongly stress the
importance of TLS being fully verified when using PLAIN.

Regards,
Matthew