Re: [TLS] draft-sheffer-tls-bcp: DH recommendations

Alex Elsayed <eternaleye@gmail.com> Tue, 24 September 2013 13:37 UTC

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Subject: Re: [TLS] draft-sheffer-tls-bcp: DH recommendations
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Peter Gutmann wrote:

<snip>
> If you do want to generate your own ECDH parameters (i.e. curves), that's
> another huge mess to deal with.  For DH you just use Lim-Lee and you're
> done (although the fact that TLS doesn't communicate the 'q' value is
> something I'd really like to see corrected), while for ECC you need to get
> an awful lot of special-case checks and conditions just right.

Bernstein and Lange have some interesting stuff regarding that in-progress; 
this presentation[1] points out that those very same special-case checks and 
conditions are made necessary by the types of curves chosen, and that by 
choosing complete, twist-secure Edwards curves those can largely be avoided.

However, neither of the NIST curves nor the Brainpool curves are Edwards 
curves at all due to not having an order 4 point.

> Then, once you've done that, you get to find out how many implementations
> support the arbitrary_explicit_prime_curves format, which I suspect is
> pretty close to zero.

Of course, this remains an issue.


[1] http://cr.yp.to/talks/2013.05.31/slides-dan+tanja-20130531-4x3.pdf