Re: [TLS] Version negotiation, take two

Andrei Popov <Andrei.Popov@microsoft.com> Wed, 14 September 2016 17:40 UTC

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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: Hubert Kario <hkario@redhat.com>, David Benjamin <davidben@chromium.org>
Thread-Topic: [TLS] Version negotiation, take two
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Date: Wed, 14 Sep 2016 17:39:59 +0000
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Subject: Re: [TLS] Version negotiation, take two
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Do you mean a TLS extension code point per TLS version?
One argument against this was that this makes it difficult to express the client's prioritization of TLS versions, but IMHO arguably the server should not care.

Cheers,

Andrei

-----Original Message-----
From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Hubert Kario
Sent: Wednesday, September 14, 2016 9:40 AM
To: David Benjamin <davidben@chromium.org>;
Cc: tls@ietf.org
Subject: Re: [TLS] Version negotiation, take two

On Wednesday, 14 September 2016 16:17:50 CEST David Benjamin wrote:
> Yes, we find list intolerance too---servers which only look at the 
> second byte in a cipher suite, servers which forgot a default in their 
> NamedGroup switch-case, servers which get confused on unknown 
> HashAlgorithms, servers which require the final extension 
> non-empty---but this is dramatically less than version intolerance. 
> It's usually within tolerable levels that we needn't resort to fallbacks.
> 
> The proposal switches from something which we know does not work to 
> something new. Perhaps this new one will break too, but it is very 
> similar to things that have worked before, and I am hopeful that GREASE will help.

Was the option to do "one extension point = specific TLS version supported" 
discussed too? What arguments are there against it?

--
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purky┼łova 99/71, 612 45, Brno, Czech Republic