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

Dave Garrett <davemgarrett@gmail.com> Wed, 03 June 2015 08:05 UTC

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From: Dave Garrett <davemgarrett@gmail.com>
To: tls@ietf.org, Tony Arcieri <bascule@gmail.com>
Date: Wed, 3 Jun 2015 04:05:47 -0400
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Cc: Geoffrey Keating <geoffk@geoffk.org>
Subject: Re: [TLS] I-D Action: draft-ietf-tls-negotiated-ff-dhe-10.txt
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On Wednesday, June 03, 2015 02:16:50 am Tony Arcieri wrote:
> Unfortunately, exactly as you've pointed out, legacy clients are
> incompatible with these stronger D-H groups. For legacy Java clients, it
> catastrophically completely prevents the TLS handshake from succeeding if
> any such ciphersuite is even present in the ServerHello.
> 
> My experience has been, and correct me if I'm wrong, that the only two ways
> to fix this are for the Java client to disable all DHE ciphersuites, or for
> the server to not offer them. Depend on the Java version, DHE with 2048-bit
> keys can break it, and for newer versions of Java, the problem persists for
> 4096-bit DHE.

On Wednesday, June 03, 2015 03:00:07 am Tony Arcieri wrote:
> I just want DHE to diediedie.
> 
> Perhaps someone can explain how keeping DHE around is actually beneficial
> in any way whatsover? Right now it's just giving me a headache and making
> me angry.

People want a backup to deal with mistrust of ECC curves and general paranoia. Though, with issues this bad, yeah, killing it seems like a sensible option. I don't think the paranoia is unwarranted, however.

> I don't see how adding more complexity fixes the problem.

Well... here's a way it could:
1) Deprecate/prohibit all "DH(E)_*" cipher suites
2) Create a new set of "FFDHE_*" cipher suites to replace them that only allow strong groups (3072+)

I'm not saying this is the best idea, but it is _an_ idea. ;)


Dave