Re: [TLS] chairs - please shutdown wiretapping discussion...

Ilari Liusvaara <ilariliusvaara@welho.com> Wed, 12 July 2017 15:08 UTC

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Date: Wed, 12 Jul 2017 18:08:31 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Christian Huitema <huitema@huitema.net>
Cc: Stephen Farrell <stephen.farrell@cs.tcd.ie>, Ted Lemon <mellon@fugue.com>, tls@ietf.org
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Subject: Re: [TLS] chairs - please shutdown wiretapping discussion...
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On Tue, Jul 11, 2017 at 01:54:40PM -0700, Christian Huitema wrote:
> On 7/11/2017 1:31 PM, Stephen Farrell wrote:
> 
> > PS: There are also genuine performance reasons why the same
> > DH public might be re-used in some cases, so there would be
> > false positives in a survey to consider as well.
> 
> Well, yes. The classic argument is performance. Saving the cost of
> exponentiation, computing G^X once for many session instead of once per
> session. But you reap most of the benefits of that optimization with a
> fairly small number of repetitions. Performance alone is not a good
> reason to use the key over extended period, not to share the exact same
> key between all servers in a farm. The fact is that wide reuse of the
> same (EC)DH private key does compromise the security of TLS -- including
> an obvious issue with forward secrecy.

Yes, the cost saturates very rapidly as the number of reuses increases.
Even 100 reuses gets one within ~1% of asymptotic limit (half load).

> In any case, I just submitted PR #1049
> (https://github.com/tlswg/tls13-spec/pull/1049).

I didn't see this document the attack on integerity (full MITM attack)
of the connection if attacker has aquired the DH share before the
connection.


-Ilari