Re: [Cfrg] Adoption of draft-ladd-spake2 as a RG document

Adam Langley <agl@imperialviolet.org> Thu, 22 January 2015 19:35 UTC

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From: Adam Langley <agl@imperialviolet.org>
To: "Dearlove, Christopher (UK)" <chris.dearlove@baesystems.com>
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Subject: Re: [Cfrg] Adoption of draft-ladd-spake2 as a RG document
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On Mon, Jan 19, 2015 at 3:56 AM, Dearlove, Christopher (UK)
<chris.dearlove@baesystems.com>; wrote:
> A minor point compared to choice of curve. Commenting on draft draft-agl-cfrgcurve-00, it indicates, in section 8 the use of little-endian order. RFC 5480 (obvious prior art in IETF) does not appear to specify big/little endianness, but delegates that to its reference SEC1. That document (http://www.secg.org/sec1-v2.pdf) in section 2.3.7 reverses the order of its x and M coefficients to produce a big-endian representation of an integer. Big endian format is also used by, for example, OpenSSL. Is the use of little endian format here a deliberate design decision?

(This appears to be a comment on draft-agl-cfrgcurve-00, but this
thread is otherwise about draft-ladd-spake2 which is why I didn't
notice it.)

Yes, the use of little-endian is a deliberate decision. It reflects
unanimous practice with the recommended curve. Also, I think there's a
general movement towards having crypto primitives specified as
functions on bytes strings rather than on more abstract concepts like
points (which I support).


Cheers

AGL

-- 
Adam Langley agl@imperialviolet.org https://www.imperialviolet.org