Re: [TLS] Limiting replay time frame of 0-RTT data

Eric Rescorla <ekr@rtfm.com> Tue, 15 March 2016 03:00 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 14 Mar 2016 19:59:50 -0700
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To: Martin Thomson <martin.thomson@gmail.com>
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Cc: Karthikeyan Bhargavan <karthik.bhargavan@gmail.com>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Limiting replay time frame of 0-RTT data
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On Mon, Mar 14, 2016 at 7:25 PM, Martin Thomson <martin.thomson@gmail.com>;
wrote:

> On 15 March 2016 at 13:22, Bill Cox <waywardgeek@google.com>; wrote:
> > In TLS 1.3, tickets are sent after the full handshake completes, after
> > encryption is enabled for the connection.  Now, if an attacker has the
> > ticket encryption key, it is not possible to decrypt old connections.  Is
> > that right?  It looks to me like tickets have real PFS in TLS 1.3.
>
>
> It's the properties of the session that matter here, not the tickets.
>
> The tickets are sent in the clear in the resumed handshake.
>

Right. As far as I can tell, that's required. TLS 1.3 PFS *is* much better
with
respect to tickets because the ticket established in connection N cannot
be used to decrypt that connection. In addition, because you can do
PSK-ECDHE,
you can confine the PFS risk to the 0-RTT data.

-Ekr