lkml.org 
[lkml]   [2018]   [Nov]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] crypto: ecc - regularize scalar for scalar multiplication
Date
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.

ecc_point_mult is already using a regular algorithm (i.e. having an
operation flow independent of the input scalar) but regularization step
is forgotten.

Regularization step is based on micro-ecc by Kenneth MacKay.

Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
---
crypto/ecc.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 8facafd67802..adcce310f646 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -842,15 +842,23 @@ static void xycz_add_c(u64 *x1, u64 *y1, u64 *x2, u64 *y2, u64 *curve_prime,

static void ecc_point_mult(struct ecc_point *result,
const struct ecc_point *point, const u64 *scalar,
- u64 *initial_z, u64 *curve_prime,
+ u64 *initial_z, const struct ecc_curve *curve,
unsigned int ndigits)
{
/* R0 and R1 */
u64 rx[2][ECC_MAX_DIGITS];
u64 ry[2][ECC_MAX_DIGITS];
u64 z[ECC_MAX_DIGITS];
+ u64 sk[2][ECC_MAX_DIGITS];
+ u64 *curve_prime = curve->p;
int i, nb;
- int num_bits = vli_num_bits(scalar, ndigits);
+ int num_bits;
+ int carry;
+
+ carry = vli_add(sk[0], scalar, curve->n, ndigits);
+ vli_add(sk[1], sk[0], curve->n, ndigits);
+ scalar = sk[!carry];
+ num_bits = sizeof(u64) * ndigits * 8 + 1;

vli_set(rx[1], point->x, ndigits);
vli_set(ry[1], point->y, ndigits);
@@ -1004,7 +1012,7 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
goto out;
}

- ecc_point_mult(pk, &curve->g, priv, NULL, curve->p, ndigits);
+ ecc_point_mult(pk, &curve->g, priv, NULL, curve, ndigits);
if (ecc_point_is_zero(pk)) {
ret = -EAGAIN;
goto err_free_point;
@@ -1090,7 +1098,7 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
goto err_alloc_product;
}

- ecc_point_mult(product, pk, priv, rand_z, curve->p, ndigits);
+ ecc_point_mult(product, pk, priv, rand_z, curve, ndigits);

ecc_swap_digits(product->x, secret, ndigits);

--
2.11.0
\
 
 \ /
  Last update: 2018-11-04 14:35    [W:0.026 / U:2.380 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site