Re: [Cfrg] A draft merging rpgecc and thecurve25519function.

Adam Langley <> Fri, 02 January 2015 01:16 UTC

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From: Adam Langley <>
To: Watson Ladd <>
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Subject: Re: [Cfrg] A draft merging rpgecc and thecurve25519function.
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On Thu, Jan 1, 2015 at 4:51 PM, Adam Langley <> wrote:
> However, I don't agree that the algorithm is simply ignored. It's
> clearly important to some that the generation algorithm be explicit
> and transparent. Yes, it's odd that at the end we have to do an
> arbitrary isogeny but I think the motivation for that is clear and
> it's a "safe" step (i.e. we can't have hidden anything dodgy in there
> to my knowledge.)
> The algorithm could be written to reflect how curve25519 was
> developed: i.e. that it output a Montgomery curve and then the twisted
> Edwards is the obvious isomorphism from there (if needed). That might
> well be clearer if we don't recommend any other curves.
> But dealing with Edwards curves and having the algorithm generate them
> makes it easier if we recommend another, or in the optimistic scenario
> that we also end up specifying a signature scheme.

I think I've fallen into the "details" trap in that reply.

However the generation is structured to make it most clear, and
whether or not we mention (twisted) Edwards curves, I think that the
important point is this:

Unless the chairs believe, and state within weeks, that we can move
forward with something shaped like this draft (whether it's based on
it or not) then I don't think that this RG will be able to recommend
any specific curves. I don't think anything will be more generally

If we can't recommend curves then the best that we might be able to do
is to put out a document that states the requirements for safe
elliptic curves and mentions that curve25519, curve25519-isogeny,
41417, Goldilocks, E-521, etc are all fine, cryptographically. Then
other WGs will have to do the picking.



Adam Langley