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Re: [TLS] version downgrade protection (was: inappropriate_fallback)

Hubert Kario <hkario@redhat.com> Thu, 09 August 2018 12:34 UTC

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From: Hubert Kario <hkario@redhat.com>
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Date: Thu, 09 Aug 2018 14:34:39 +0200
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Subject: Re: [TLS] version downgrade protection (was: inappropriate_fallback)
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On Thursday, 9 August 2018 13:57:20 CEST Peter Gutmann wrote:
> Benjamin Kaduk <bkaduk@akamai.com> writes:
> >A 1.2-capable implementation that is configured to only offer 1.1 should be
> >able to behave similarly.
> 
> Except that it can't, because as soon as the server indicates use of TLS
> 1.1, the client is required to abort the handshake.  Thus no one can use
> TLS 1.1 or below, because the client is required to abort the handshake if
> the server indicates it's using this.

the signalling bytes must be included only if server has support for higher 
protocol versions enabled; if TLS 1.2 and TLS 1.3 is explicitly disabled on 
the server, it must not include those signalling bytes

-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 115, 612 00  Brno, Czech Republic

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