Re: [TLS] analysis of wider impact of TLS1.3 replayabe data

Ilari Liusvaara <ilariliusvaara@welho.com> Mon, 14 March 2016 06:23 UTC

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Date: Mon, 14 Mar 2016 08:23:08 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Harlan Lieberman-Berg <hlieberman@setec.io>
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Cc: Scott Schmit <i.grok@comcast.net>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] analysis of wider impact of TLS1.3 replayabe data
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On Sun, Mar 13, 2016 at 09:26:14PM -0400, Harlan Lieberman-Berg wrote:
> 
> I agree with a slight tweak in wording here, Bill.  I think that we
> /should/ drop the parts of 0-RTT where we are not confident that an
> admin who blindly enables functionality in TLS 1.3 will not end up
> harming themselves.
> 
> More generally, I strongly believe that TLS 1.3 should not
> provide options which we think should be restricted to "admins who know
> what they're doing".  These end up hurting us down the line (cf EXPORT
> cipher suites.)
> 
> I think we should ship the parts of 0-RTT that we believe are
> intrinsically safe for (the vast majority) of the internet to enable and
> use on day 1.

Here are what I think would be reasonable restrictions on 0-RTT:
- Require labeling the application protocol 0RTT data is for.
  * To prevent cross-protocol attacks.
- Require application protocol to profile the semantics of 0RTT data.
  * To at least get some idea of protocol-level security properties.
  * Some applications might need to handle 0RTT specially for
    security reasons (HTTP/2?)
- Require application to specifically request 0RTT data.
  * To prevent unaware applications from thinking it has the same
    properties as main data.
- Require 0RTT data to be kept separate from main application data.
  * To make more difficult for applications to mix it up.
- Ensure that no 0RTT mode invokes screwy cryptographic behaviour.
  * Famous last words: "Not believed to be exploitable".


And none of these should be subject to "admin configuration"
(disabling entiere 0-RTT is).


-Ilari