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Re: [TLS] Security review of TLS1.3 0-RTT

Ilari Liusvaara <ilariliusvaara@welho.com> Fri, 02 June 2017 07:57 UTC

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Date: Fri, 02 Jun 2017 10:57:18 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Colm MacCárthaigh <colm@allcosts.net>
Cc: Eric Rescorla <ekr@rtfm.com>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Security review of TLS1.3 0-RTT
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On Thu, Jun 01, 2017 at 11:20:56PM -0700, Colm MacCárthaigh wrote:
> 
> Maybe a lot of this dilemma could be avoided if the the PSKs that can be
> used for regular resumption and for 0-RTT encryption were separate, with
> the latter being scoped smaller and with use-at-most-once semantics.

The problem here is that the scoping rules can be impossible for the
client to understand (there is possibly anycast involved!)


And also, more serious problem: I thought that server could send
tickets that can't be used for 0-RTT. And this was true a few drafts
back, but now it seems to have gotten lost (at least I can't find
the appropriate requirements). This is a problem, because it forces
any server that implements tickets to deal with at least ignoring
0-RTT (trial decryptions!). Which is complexity that I rather not
have in servers that don't truly implement 0-RTT.



-Ilari

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