diff options
| author | Vitaly Chikunov <vt@altlinux.org> | 2018-11-11 20:40:02 +0300 |
|---|---|---|
| committer | Herbert Xu <herbert@gondor.apana.org.au> | 2018-11-16 14:11:04 +0800 |
| commit | 3da2c1dfdb802b184eea0653d1e589515b52d74b (patch) | |
| tree | 2f5689d4508f993fc477ce5dbdb35c6e76d6ff8b /crypto/ecc.c | |
| parent | 8a5a79d5556b822143b4403fc46068d4eef2e4e2 (diff) | |
crypto: ecc - regularize scalar for scalar multiplication
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@altlinux.org>
Cc: kernel-hardening@lists.openwall.com
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto/ecc.c')
| -rw-r--r-- | crypto/ecc.c | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/crypto/ecc.c b/crypto/ecc.c index 9d24e6522730..ed1237115066 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); @@ -1014,7 +1022,7 @@ 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; @@ -1100,7 +1108,7 @@ 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); |