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Message-ID: <20181116061958.yary7zcu5m3pnolb@gondor.apana.org.au>
Date: Fri, 16 Nov 2018 14:19:58 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Vitaly Chikunov <vt@...linux.org>
Cc: "David S. Miller" <davem@...emloft.net>, linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2] crypto: ecc - regularize scalar for scalar
multiplication
On Sun, Nov 11, 2018 at 08:40:02PM +0300, Vitaly Chikunov wrote:
> ecc_point_mult is supposed to be used with a regularized scalar,
> otherwise, it's possible to deduce the position of the top bit of the
> scalar with timing attack. This is important when the scalar is a
> private key.
>
> ecc_point_mult is already using a regular algorithm (i.e. having an
> operation flow independent of the input scalar) but regularization step
> is not implemented.
>
> Arrange scalar to always have fixed top bit by adding a multiple of the
> curve order (n).
>
> References:
> The constant time regularization step is based on micro-ecc by Kenneth
> MacKay and also referenced in the literature (Bernstein, D. J., & Lange,
> T. (2017). Montgomery curves and the Montgomery ladder. (Cryptology
> ePrint Archive; Vol. 2017/293). s.l.: IACR. Chapter 4.6.2.)
>
> Signed-off-by: Vitaly Chikunov <vt@...linux.org>
> Cc: kernel-hardening@...ts.openwall.com
> ---
>
> Changes from v1:
> - No code changes, only description updates to be more informative.
>
> crypto/ecc.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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