Re: [TLS] draft-davidben-tls-grease-01

Hubert Kario <hkario@redhat.com> Mon, 05 September 2016 16:09 UTC

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From: Hubert Kario <hkario@redhat.com>
To: David Benjamin <davidben@chromium.org>
Date: Mon, 05 Sep 2016 18:09:08 +0200
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Subject: Re: [TLS] draft-davidben-tls-grease-01
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On Monday, 5 September 2016 15:55:49 CEST David Benjamin wrote:
> On Mon, Sep 5, 2016 at 10:59 AM Hubert Kario <hkario@redhat.com> wrote:
> > On the other hand, the implementation I work on keeps the sent Client
> > Hello on
> > hand and checks the server response against the exact values it sent.
> > 
> > So for it, server selecting GREASE value would be fine, it would fail at
> > key
> > exchange processing time.
> > 
> > Keeping the Client Hello in case server asks for certificate verification
> > is
> > not entirely unheard of either.
> > 
> > So I think it's best to keep the specification implementation agnostic,
> > without any assumptions about how the code is written, and describe just
> > the
> > externally visible behaviour. But describe it fully.
> 
> The document does that, no? Or are you simply asking that I remove the "no
> special processing sentence. Happy to do that.
> 
> (I'm assuming your implementation then handles the renegotiate_info SCSV
> and FALLBACK_SCSV similarly special? It's the same story with those two.)

yes, it handles them specially, but that's actually by a happy coincidence: 
client needs to verify that the ciphersuite can be negotiated with a TLS 
version selected by server and you can't negotiate those two ciphers with any 
version (in other words, this is a result of self-consistency check on server 
hello, not explicit check against them)

-- 
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