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

Peter Gutmann <pgut001@cs.auckland.ac.nz> Mon, 31 October 2016 10:07 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: jonas weber <jonasweber86@yandex.com>, "cfrg@irtf.org" <cfrg@irtf.org>
Thread-Topic: [Cfrg] What groups to use for Diffie Hellman?
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Date: Mon, 31 Oct 2016 10:07:32 +0000
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Subject: Re: [Cfrg] What groups to use for Diffie Hellman?
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jonas weber <jonasweber86@yandex.com>; writes:

>Given the uncertainty over the RFC-5114 groups, I believe it would be helpful
>to have an RFC with a list of primes as you describe. Many of us use shorter
>exponents to save computation and having a list of verifiable primes would be
>useful, particularly if they could be registered for use in IKE and TLS.

I've been having a discussion about this off-list, may as well make it public
if others are interested... the main issue is how to generate the values,
presumably you'd want safe primes (so p = 2q + 1), g = 2 for efficiency, and
some NUMS source for the primes.  One suggestion was PBKDF2( "DH 2048" ),
PBKDF2( "DH 1024" ), etc as the seed value and then some deterministic way to
get from there to the final prime.  And maybe pseudocode so anyone can
replicate it using whatever bignum library they prefer (rather than, say,
"plug the following formula into Mathematica").  How NUMS does it have to get?

Peter.