Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-10.txt

Tony Arcieri <bascule@gmail.com> Wed, 03 June 2015 08:49 UTC

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From: Tony Arcieri <bascule@gmail.com>
Date: Wed, 3 Jun 2015 01:48:56 -0700
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To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
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Cc: Geoffrey Keating <geoffk@geoffk.org>, TLS WG <tls@ietf.org>
Subject: Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-10.txt
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On Wed, Jun 3, 2015 at 1:43 AM, Peter Gutmann <pgut001@cs.auckland.ac.nz>
wrote:

>  You seem to want everyone to change their behaviour in order to
> accommodate
> the fact that you've chosen to use a broken, buggy implementation
>

These aren't clients under my control. I am talking about an entire
language ecosystem here, not just my little corner of the world. But even
if they were my clients, they wouldn't negotiate DHE anyway, because most
configurations would prefer ECDHE.

The "accommodation" you're defending is using finite-field Diffie-Hellman.
Most clients support ECDH(E) and don't need to support finite-field
Diffie-Hellman.

Finite field Diffie-Hellman is a slow, outmoded legacy key exchange
algorithm that in my opinion should completely be abandoned.

I didn't even bring up Java, but it was cited as a reason for FFDHE to
exist. However Java 7 and 8 clients would prefer ECDHE anyway. As they
should, it's faster and uses smaller keys.

This is a case of some legacy gunk left over from the early days of TLS
breaking key exchange for clients that support better algorithms.

We can either double down on the gunk, or shut it off.

*In practice* I have been telling people to shut it off and so far it's
been a successful solution to the problem.

Why should we keep this legacy gunk around? Who is it helping?

-- 
Tony Arcieri