Re: [TLS] draft-dkg-tls-reject-static-dh

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 07 December 2018 06:31 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>, Stephen Farrell <stephen.farrell@cs.tcd.ie>
CC: "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] draft-dkg-tls-reject-static-dh
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Date: Fri, 7 Dec 2018 06:31:21 +0000
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Subject: Re: [TLS] draft-dkg-tls-reject-static-dh
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Daniel Kahn Gillmor <dkg@fifthhorseman.net> writes:

>the way i was going to write it that guidance was pretty dumb (i was thinking
>of just a hashtable combined with a fixed-size ring buffer to be constant-
>space and roughly constant-time, and hadn't even considered bloom filters),
>so i welcome suggested text.

Aren't you going to get into an adversarial machine learning problem where
your recogniser has to be smarter than the other side's DH-reuse code?  In
other words if the server just reuses the same DHE public value again and
again you can detect it, but if they generate slightly different values from a
fixed seed or start point you're not going to be able to detect it unless you
know what they're doing.

Not to mention a NOBUS DHE public value if they really want to be crafty.  In
other words if someone wants to middlebox TLS, they're going to do it no
matter how much people may dislike it.

Peter.