*
*/
+#define OPENSSL_FIPSAPI
+
#include <openssl/err.h>
#include "ec_lcl.h"
+#ifndef OPENSSL_NO_EC2M
+
/* Compute the x-coordinate x/z for the point 2*(x/z) in Montgomery projective
* coordinates.
return ret;
}
+
/* Computes scalar*point and stores the result in r.
* point can not equal r.
- * Uses algorithm 2P of
+ * Uses a modified algorithm 2P of
* Lopez, J. and Dahab, R. "Fast multiplication on elliptic curves over
* GF(2^m) without precomputation" (CHES '99, LNCS 1717).
+ *
+ * To protect against side-channel attack the function uses constant time swap,
+ * avoiding conditional branches.
*/
static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
const EC_POINT *point, BN_CTX *ctx)
x2 = &r->X;
z2 = &r->Y;
+ bn_wexpand(x1, group->field.top);
+ bn_wexpand(z1, group->field.top);
+ bn_wexpand(x2, group->field.top);
+ bn_wexpand(z2, group->field.top);
+
if (!BN_GF2m_mod_arr(x1, &point->X, group->poly)) goto err; /* x1 = x */
if (!BN_one(z1)) goto err; /* z1 = 1 */
if (!group->meth->field_sqr(group, z2, x1, ctx)) goto err; /* z2 = x1^2 = x^2 */
word = scalar->d[i];
while (mask)
{
- if (word & mask)
- {
- if (!gf2m_Madd(group, &point->X, x1, z1, x2, z2, ctx)) goto err;
- if (!gf2m_Mdouble(group, x2, z2, ctx)) goto err;
- }
- else
- {
- if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;
- if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;
- }
+ BN_consttime_swap(word & mask, x1, x2, group->field.top);
+ BN_consttime_swap(word & mask, z1, z2, group->field.top);
+ if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;
+ if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;
+ BN_consttime_swap(word & mask, x1, x2, group->field.top);
+ BN_consttime_swap(word & mask, z1, z2, group->field.top);
mask >>= 1;
}
mask = BN_TBIT;
int ret = 0;
size_t i;
EC_POINT *p=NULL;
+ EC_POINT *acc = NULL;
if (ctx == NULL)
{
}
if ((p = EC_POINT_new(group)) == NULL) goto err;
+ if ((acc = EC_POINT_new(group)) == NULL) goto err;
- if (!EC_POINT_set_to_infinity(group, r)) goto err;
+ if (!EC_POINT_set_to_infinity(group, acc)) goto err;
if (scalar)
{
if (!ec_GF2m_montgomery_point_multiply(group, p, scalar, group->generator, ctx)) goto err;
- if (BN_is_negative(scalar))
+ if (BN_is_negative(scalar))
if (!group->meth->invert(group, p, ctx)) goto err;
- if (!group->meth->add(group, r, r, p, ctx)) goto err;
+ if (!group->meth->add(group, acc, acc, p, ctx)) goto err;
}
for (i = 0; i < num; i++)
if (!ec_GF2m_montgomery_point_multiply(group, p, scalars[i], points[i], ctx)) goto err;
if (BN_is_negative(scalars[i]))
if (!group->meth->invert(group, p, ctx)) goto err;
- if (!group->meth->add(group, r, r, p, ctx)) goto err;
+ if (!group->meth->add(group, acc, acc, p, ctx)) goto err;
}
+ if (!EC_POINT_copy(r, acc)) goto err;
+
ret = 1;
err:
if (p) EC_POINT_free(p);
+ if (acc) EC_POINT_free(acc);
if (new_ctx != NULL)
BN_CTX_free(new_ctx);
return ret;
{
return ec_wNAF_have_precompute_mult(group);
}
+
+#endif