Re: [Cfrg] Safecurves draft

Watson Ladd <watsonbladd@gmail.com> Wed, 08 January 2014 19:07 UTC

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Date: Wed, 8 Jan 2014 11:07:24 -0800
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From: Watson Ladd <watsonbladd@gmail.com>
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Subject: Re: [Cfrg] Safecurves draft
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On Wed, Jan 8, 2014 at 10:40 AM, Manuel Pégourié-Gonnard <mpg@elzevir.fr> wrote:
> On 08/01/2014 18:11, Watson Ladd wrote:
>> draft-ladd-safecurves contains the Safecurves with orders
>> 2^255+\epsilon and higher.
>> I forgot to update the TOC, but that shouldn't stop the substantive
>> conversation.
>>
>> Does anyone object to these curves being approved for IETF standard
>> body use/typos/general nastiness?
>
> I'm in favour of these curves being approved for IETF use.
>
> I think the draft itself, however, should be expanded to go into some details
> about the advantages of the curves and the differences with existing curves.
>
> I have one question about the curves themselves: why are there two Montgomery
> curves over GF(2^383-187)? I thought the curves were chosen by a deterministic
> process, and the smallest 'a' coefficient giving the desired properties was
> always used.

It's because one has an Elligator map and the other does not. Some
applications require
it, but not all.

>
> Also, is it on purpose that you didn't include E-521 in your draft?

I simply copied the safecurves.cr.yp.to list starting at Curve25519.
There is no E-521 on that list.

>
> Manuel.
>
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