Re: [Cfrg] Efficient side channel resistance for X25519..

Phillip Hallam-Baker <phill@hallambaker.com> Tue, 12 November 2019 17:38 UTC

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References: <CAMm+LwiB6cpcnb_gpfXueU-A5w=jJ-4U5hhH_xkH5ERx1budoQ@mail.gmail.com> <20191109190705.j4b7chrjfev3lwig@positron.jfet.org> <CAMm+LwhRA3zTMdMM0U-qbC47i80LF8PyN9hX3bzVy_kddHisCw@mail.gmail.com> <810C31990B57ED40B2062BA10D43FBF501E82D65@XMB116CNC.rim.net> <CA+jiKjP1aQ_dYGUdiU==GRKuN392z-z884jfCmDRHoMRFnbLLA@mail.gmail.com>
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From: Phillip Hallam-Baker <phill@hallambaker.com>
Date: Tue, 12 Nov 2019 12:38:33 -0500
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To: Henry de Valence <ietf@hdevalence.ca>
Cc: Dan Brown <danibrown@blackberry.com>, "rsw@jfet.org" <rsw@jfet.org>, "cfrg@irtf.org" <cfrg@irtf.org>
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Subject: Re: [Cfrg] Efficient side channel resistance for X25519..
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Thanks,

It looks to me as if Algorithm 5 should do what I need. Though I will have
to work out the correspondence between Algorithm 4 and RFC 7748.

Probably not happening till I get back from Singapore.



On Mon, Nov 11, 2019 at 5:17 PM Henry de Valence <ietf@hdevalence.ca>; wrote:

> On Sun, Nov 10, 2019 at 6:56 AM Dan Brown <danibrown@blackberry.com>;
> wrote:
> >
> > Recovering y at end of Montgomery ladder is something I heard about from
> Scott Vanstone, so it is likely published.
>
> Section 4.3 of https://arxiv.org/pdf/1703.01863.pdf may be helpful.
>
> Cheers,
> Henry
>