Re: [TLS] 0-RTT and Anti-Replay

Eric Rescorla <ekr@rtfm.com> Mon, 23 March 2015 13:12 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 23 Mar 2015 08:11:59 -0500
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To: Nico Williams <nico@cryptonector.com>
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Subject: Re: [TLS] 0-RTT and Anti-Replay
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On Mon, Mar 23, 2015 at 3:47 AM, Nico Williams <nico@cryptonector.com>;
wrote:

> On Sun, Mar 22, 2015 at 02:49:28PM -0700, Eric Rescorla wrote:
> > Now consider what happens when the server reboots and loses its
> > state. You don't want to reject every client 0-RTT connection so
> > instead what you do is you ignore the client's initial data sent in
> > the first flight. Since the ServerHello provides a new Random value,
> > any data the client sends in subsequent flights has the usual
> > anti-replay protection.
>
> This is an optimization.
>
> If the server loses its replay state then it must cause every 0-RTT
> connection to become a 1-RTT connection.  There's no question of "want".
>

Maybe I wasn't clear. When I said "reject" I meant "hard-fail" rather than
make it 1-RTT.

-Ekr

Nico
> --
>