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Re: Bug#766395: emacs/gnus: Uses s_client to for SSL.

From: Lars Magne Ingebrigtsen
Subject: Re: Bug#766395: emacs/gnus: Uses s_client to for SSL.
Date: Sat, 25 Oct 2014 17:53:52 +0200
User-agent: Gnus/5.130012 (Ma Gnus v0.12) Emacs/25.0.50 (gnu/linux)

Ted Zlatanov <address@hidden> writes:

> I really need to know if GnuTLS can interact with Emacs Lisp during the
> negotiation phases through C callbacks, because if it can, we'll be able
> to catch and remedy these situations.  We discussed that earlier when
> Toke submitted the TOFU patch and I'd appreciate some help.

The proposed security manager would store certificate fingerprints, so
detecting when a known server drops from TLS 1.2 to SSL 3.0 would
presumably also be something we could warn about, just like we would
warn when we drop from STARTTLS to unencrypted.

"You are talking to imap:dea.gov via SSL 3.0 now, while last time you
did this via TLS 1.2.  This might mean that you're suffering from a
Man-In-The-Middle attack.  Still connect?"

I'm not actually sure we need a callback to handle this stuff.  I've
just looked very briefly at the libgnutls interface, and it kinda seems
to me like we could just do the connection, and then decide whether
we're satisfied with its properties (SSL 3.0, changed certificate,
privately signed certificate, etc) on the Emacs side.

But I'm quite likely misunderstanding something about how libgnutls
negotiates the connection.

(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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