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Re: [TLS] On Curve25519 and other possibilities (e.g. ietf256p, ietf384p, ietf521p,

Watson Ladd <watsonbladd@gmail.com> Fri, 04 July 2014 15:15 UTC

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Date: Fri, 04 Jul 2014 08:15:32 -0700
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From: Watson Ladd <watsonbladd@gmail.com>
To: Johannes Merkle <johannes.merkle@secunet.com>
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Subject: Re: [TLS] On Curve25519 and other possibilities (e.g. ietf256p, ietf384p, ietf521p,
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On Fri, Jul 4, 2014 at 7:59 AM, Johannes Merkle
<johannes.merkle@secunet.com> wrote:
> Alyssa Rowan wrote on 27.06.2014 08:46:
>> Brainpool has already generated a set of 'random' primes, but random primes are extremely slow to implement - and
>> in the case of Brainpool, the 256-bit curve has extremely unfortunate lack of twist security, so any implementation
>> that tries to skip validation is in really big trouble.
>
> Why should anyone try to skip validation? In order to improve performance by less than 1%?

Implementations frequently expose an API where validation is separate
from group operations, and people
just forget to make the call sometimes.

Furthermore, with anything other than a compressed format it's not
just twist security, but any security that failure of point validation
harms.
I send point on a curve with smooth order, and extract the key. I send
point on curve with small order, and dictate the key, etc.

Twist security matters for Joyce-Briers ladders only, as far as I know
on Weierstrass curves. Other formulas use the y coordinates.

Sincerely,
Watson Ladd
>
>
> --
> Johannes
>
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