Re: [TLS] supported_versions question

Kurt Roeckx <kurt@roeckx.be> Mon, 31 October 2016 22:21 UTC

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Date: Mon, 31 Oct 2016 23:20:58 +0100
From: Kurt Roeckx <kurt@roeckx.be>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
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References: <CAMoSCWaVJy9f6NFy1Msc1_VSDxRFM2pruhecWb+22N4ct-t0+g@mail.gmail.com> <20161031185724.GA23357@LK-Perkele-V2.elisa-laajakaista.fi> <CAF8qwaCe89epMMzCA0BNfXWss9FWpDze8ScydufdoTNTNqmW1g@mail.gmail.com> <20161031193010.GC23357@LK-Perkele-V2.elisa-laajakaista.fi>
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Cc: David Benjamin <davidben@google.com>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] supported_versions question
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On Mon, Oct 31, 2016 at 09:30:10PM +0200, Ilari Liusvaara wrote:
> On Mon, Oct 31, 2016 at 07:11:10PM +0000, David Benjamin wrote:
> > 
> > We could say the versions extension only applies to 1.2 and up. I.e. don't
> > bother advertising 1.1 and 1.0 as a client and servers ignore 1.1 and 1.0
> > when they see them in the version list. That keeps the protocol deployable
> > on the Internet as it exists, avoids having to evaluate too versioning
> > schemes (if you see the extension, you don't bother reading legacy_version
> > at all), while avoiding the weird behavior where, given this ClientHello:
> > 
> >    legacy_version: TLS 1.2
> >    supported_versions: {TLS 1.1}
> > 
> > TLS 1.3 says to negotiate TLS 1.1 and TLS 1.2 says to negotiate TLS 1.2.
> 
> Yeah, I don't think it ever makes sense to stick TLS 1.0 or 1.1 into
> supported_versions. There are good reasons to stick TLS 1.2 there tho.

Can you give some more details about those good reasons?


Kurt