Re: [Cfrg] Safecurves draft

Manuel Pégourié-Gonnard <mpg@elzevir.fr> Wed, 08 January 2014 19:27 UTC

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Subject: Re: [Cfrg] Safecurves draft
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On 08/01/2014 20:07, Watson Ladd wrote:
> On Wed, Jan 8, 2014 at 10:40 AM, Manuel Pégourié-Gonnard <mpg@elzevir.fr> wrote:
>> 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.
> 
Ok, thanks for the info.

Since their respective 'a' coefficients are of comparable sizes (18 vs 21 bits),
I expect their performances will be very comparable, so I wonder if it's worth
standardizing both of them, rather than just the one with the Elligator map.

> I simply copied the safecurves.cr.yp.to list starting at Curve25519.
> There is no E-521 on that list.
> 
IMHO there should be :) See http://eprint.iacr.org/2013/647

Manuel.