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Re: [Cfrg] Point format endian

Derek Atkins <derek@ihtfp.com> Tue, 27 January 2015 15:41 UTC

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From: Derek Atkins <derek@ihtfp.com>
To: Stephen Farrell <stephen.farrell@cs.tcd.ie>
References: <9A043F3CF02CD34C8E74AC1594475C73AAF68325@uxcn10-tdc05.UoA.auckland.ac.nz> <54C76EED.6090205@cs.tcd.ie>
Date: Tue, 27 Jan 2015 10:41:11 -0500
In-Reply-To: <54C76EED.6090205@cs.tcd.ie> (Stephen Farrell's message of "Tue, 27 Jan 2015 10:56:45 +0000")
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Cc: "'cfrg@irtf.org'" <cfrg@irtf.org>, Peter Gutmann <pgut001@cs.auckland.ac.nz>
Subject: Re: [Cfrg] Point format endian
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Stephen Farrell <stephen.farrell@cs.tcd.ie> writes:

> On 27/01/15 10:34, Peter Gutmann wrote:
>> The universal standard for crypto bignums is big-endian
>
> Hmmm.... sez who? :-)

PKIX, OpenPGP, OpenSSH, Kerberos, TLS...  Pretty much every existing
IETF security standard I know of to date encodes numbers in big-endian
format.

> But seriously, if in fact this makes little or no difference,
> which I believe is the case, and which I believe you are also
> arguing, then what is the problem with going with the initial
> coder's choice here?
>
> If there is no problem then just doing that and making sure
> it's properly documented should be just fine I'd have thought.

It would mean a completely separate code path to support 25519 versus
supporting most (all?) existing ECC curves.

> S.

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

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