Re: [TLS] [PSA] 0-RTT tolerance is mandatory

Ilari Liusvaara <ilariliusvaara@welho.com> Wed, 04 July 2018 13:08 UTC

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Date: Wed, 4 Jul 2018 16:06:27 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Hubert Kario <hkario@redhat.com>
Cc: tls@ietf.org
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Subject: Re: [TLS] [PSA] 0-RTT tolerance is mandatory
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On Wed, Jul 04, 2018 at 02:42:51PM +0200, Hubert Kario wrote:
> All the implementations I deal with in my day-to-day work fail to handle the 
> 0-RTT client hello correctly when the 0-RTT support is not enabled on the 
> server.
> 
> I.e. they ignore the MUST clause from
> https://tools.ietf.org/html/draft-ietf-tls-tls13-28#page-58 stating that the 
> server can handle an early_data extension (and following encrypted data) in 
> only one of three ways, neither which allows for unconditional connection 
> abort.
> 
> This also runs afoul the recommendation from https://tools.ietf.org/html/
> draft-ietf-tls-tls13-28#section-D.3 on 0-RTT backwards compatibility.

OTOH, such servers probably do not send out tickets allowing 0-RTT, so
any client attempting 0-RTT with such server is very broken.


-Ilari