Re: [Cfrg] I-D Action: draft-irtf-cfrg-hpke-02.txt

Ilari Liusvaara <ilariliusvaara@welho.com> Sat, 07 December 2019 09:50 UTC

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Date: Sat, 7 Dec 2019 11:50:03 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: "cfrg@irtf.org" <cfrg@irtf.org>
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Subject: Re: [Cfrg] I-D Action: draft-irtf-cfrg-hpke-02.txt
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On Fri, Dec 06, 2019 at 07:11:01PM -0800, Benjamin Kaduk wrote:
> On Wed, Dec 04, 2019 at 11:29:53AM +0000, Michael Scott wrote:
> > 
> > Some feed-back: It would be a good idea to explicitly warn the reader that
> > the X25519/X448 keys are actually in little-endian format, whereas for
> > P256/521 they are big-endian.
> 
> I think the general idea is that X25519 and X448 APIs act on fixed-length
> byte strings and you are not supposed to care about the internal structure
> or encoding.  

Correct, from RFC7748:

"Although the functions work internally with integers, the inputs and
outputs are 32-byte strings (for X25519) or 56-byte strings (for X448)
and this specification defines their encoding."


-Ilari