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 <redacted>
Cc: kernel-hardening@lists.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 [off-list ref]
Home Page: http://gondor.apana.org.au/~herbert/
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