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Re: [Cfrg] Point format endian (was: Adoption of draft-ladd-spake2 as a RG document)

Watson Ladd <watsonbladd@gmail.com> Sat, 24 January 2015 01:10 UTC

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Date: Fri, 23 Jan 2015 17:10:12 -0800
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From: Watson Ladd <watsonbladd@gmail.com>
To: Dan Harkins <dharkins@lounge.org>
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Cc: "cfrg@irtf.org" <cfrg@irtf.org>
Subject: Re: [Cfrg] Point format endian (was: Adoption of draft-ladd-spake2 as a RG document)
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On Jan 23, 2015 2:44 PM, "Dan Harkins" <dharkins@lounge.org> wrote:
>
>
>
> On Mon, January 19, 2015 4:27 am, Alyssa Rowan wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA512
> >
> > On 19 January 2015 11:56:27 GMT+00:00, "Dearlove, Christopher (UK)"
> > <chris.dearlove@baesystems.com> wrote:
> >> […] Is the use of little endian format here a deliberate design
> >> decision?
> >
> > Probably yes, to match every existing implementation of Curve25519
already
> > in the wild (and most commonly-used architectures)?
>
>   So a long-standing tradition of the on-the-wire format is changed
because
> of the way the first curve25519 library was written? That's a weak
> justification.

And this breaks what exactly? Picking big endian means picking a different
name at a minimum to avoid confusion. It means that already deployed SSH
installations either change or confuse everyone. It means that all existing
implementations become unusable, despite extensive review and verification
efforts.

What is actually gained from using big-endian?

Sincerely,
Watson Ladd

>
>   Dan.
>
> > TLS WG give new curves free reign on point format, explicitly not SEC1
> > constrained. They preferred little endian (weakly) for the above
reason, I
> > believe?
> >
> > - --
> > /akr
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> > -----END PGP SIGNATURE-----
> >
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