Re: [Cfrg] draft-irtf-cfrg-eddsa - Implementation failure for 448

Ilari Liusvaara <ilariliusvaara@welho.com> Wed, 20 July 2016 12:49 UTC

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Date: Wed, 20 Jul 2016 15:49:04 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Jim Schaad <ietf@augustcellars.com>
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Subject: Re: [Cfrg] draft-irtf-cfrg-eddsa - Implementation failure for 448
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On Wed, Jul 20, 2016 at 02:18:52PM +0200, Jim Schaad wrote:
> There is a difference between the document and the code for point addition
> of 448.  Which is the correct one?
> 
> Text in section 5.2.4
> 
>     X3 = A*G*(H-C-D)
>     Y3 = A*G*(D-C)
> 
> Python Code
>         tmp.x=zcp*F*((self.x+self.y)*(y.x+y.y)-xcp-ycp)
>         tmp.y,tmp.z=zcp*G*(ycp-xcp),F*G
> 
> Note that the first uses A*G the section uses A*F in computing the new x
> value.

Good catch: It should be A*F (as in code). Fixed in Editor's Copy.


-Ilari