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Re: [Cfrg] Point format endian

Derek Atkins <derek@ihtfp.com> Tue, 27 January 2015 16:12 UTC

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From: Derek Atkins <derek@ihtfp.com>
To: "Salz, Rich" <rsalz@akamai.com>
References: <9A043F3CF02CD34C8E74AC1594475C73AAF68325@uxcn10-tdc05.UoA.auckland.ac.nz> <54C76EED.6090205@cs.tcd.ie> <sjm386wjko8.fsf@securerf.ihtfp.org> <b2b8d964885246748ebde894064b6a3c@ustx2ex-dag1mb2.msg.corp.akamai.com>
Date: Tue, 27 Jan 2015 11:12:22 -0500
In-Reply-To: <b2b8d964885246748ebde894064b6a3c@ustx2ex-dag1mb2.msg.corp.akamai.com> (Rich Salz's message of "Tue, 27 Jan 2015 15:46:28 +0000")
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Cc: Peter Gutmann <pgut001@cs.auckland.ac.nz>, "'cfrg@irtf.org'" <cfrg@irtf.org>
Subject: Re: [Cfrg] Point format endian
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"Salz, Rich" <rsalz@akamai.com> writes:

>> It would mean a completely separate code path to support 25519 versus
>> supporting most (all?) existing ECC curves.
>
> Don't they have a different code path for the math implementation?

Maybe.  Maybe not.  A modmult is a modmult (to some degree).

> If the parsing/serialization special-code so onerous?  If so,
> shouldn't we have the Y coordinate?

Anything new and different is onerous.  ;-) It means additional work
in terms of implementation, testing, validation, and interop.

My point is that there's years (decades, even) of standards and
implementation that parse network-byte-order numbers, even when the
local system is little-endian.  I don't see a good reason to change
that.  The only real argument I've seen is "well, the initial
implementation didn't do it that way, and other people have therefore
not done it that way."

-derek

-- 
       Derek Atkins                 617-623-3745
       derek@ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant

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