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Re: [Cfrg] What groups to use for Diffie Hellman?

Peter Gutmann <pgut001@cs.auckland.ac.nz> Tue, 01 November 2016 00:57 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Phillip Hallam-Baker <phill@hallambaker.com>
Thread-Topic: [Cfrg] What groups to use for Diffie Hellman?
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Date: Tue, 01 Nov 2016 00:57:24 +0000
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Cc: jonas weber <jonasweber86@yandex.com>, "cfrg@irtf.org" <cfrg@irtf.org>
Subject: Re: [Cfrg] What groups to use for Diffie Hellman?
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Phillip Hallam-Baker <phill@hallambaker.com> writes:


>The way I got suckered into RFC5441 is that it is the only RFC that appears
>to be consistent with RFC2631 on how to do DH:
>
>https://www.ietf.org/rfc/rfc2631.txt

Hmm, so going back one step in the chain, how did you get suckered into using
RFC 2631?  That's a spec that's used by, approximately, nothing...

(I'd have to check what IPsec does, but it's not used by TLS, SSH, S/MIME,
PGP, or any other protocol I'm familiar with.  If you need some sort of spec
for DH then I guess it's some sort of spec, but I think a better choice would
have been the TLS form, which means you get support in crypto libs, PKCS #11,
hardware, ...).

>I see the following ways forward:

Given that 5114 is unsafe and 2631 isn't used by anything that I'm aware of, I
think a better option would be:

4) Do a draft with values created in a generally-approved NUMS manner, g = 2
   for efficiency, safe primes, etc, whose generation is verified by two or
   more generally-trusted crypto people.

Peter.

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