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

Eric Rescorla <ekr@rtfm.com> Fri, 02 June 2017 13:59 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 02 Jun 2017 06:58:59 -0700
Message-ID: <CABcZeBNQHvnysLK-V0N5b=0z4=a55+3XEv1_H9BQafNmqE+Y0Q@mail.gmail.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
Cc: Colm MacCárthaigh <colm@allcosts.net>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Security review of TLS1.3 0-RTT
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It's still there, in 4.6.1.

"The sole extension currently defined for NewSessionTicket is “early_data”,
indicating that the ticket may be used to send 0-RTT data (Section 4.2.9
<https://tlswg.github.io/tls13-spec/#early-data-indication>)). It contains
the following value:"

-Ekr


On Fri, Jun 2, 2017 at 12:57 AM, Ilari Liusvaara <ilariliusvaara@welho.com>
wrote:

> 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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