X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=crypto%2Fec%2Fec2_mult.c;h=06405d0716fff0c4d5c82af2b4f6967f0d87badf;hb=f063e30fe9f316067950bdf0397b51cf87d4b6a6;hp=ab631a50a22cbdcc94dc26610f61f9b57dfd5e08;hpb=ea71ec1b11e585b3cd704af1930c09c0c1606916;p=oweals%2Fopenssl.git

diff --git a/crypto/ec/ec2_mult.c b/crypto/ec/ec2_mult.c
index ab631a50a2..06405d0716 100644
--- a/crypto/ec/ec2_mult.c
+++ b/crypto/ec/ec2_mult.c
@@ -67,10 +67,14 @@
  *
  */
 
+#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.
@@ -206,11 +210,15 @@ static int gf2m_Mxy(const EC_GROUP *group, const BIGNUM *x, const BIGNUM *y, BIG
 	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)
@@ -244,6 +252,11 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r,
 	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 */
@@ -268,16 +281,12 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r,
 		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;
@@ -319,6 +328,7 @@ int ec_GF2m_simple_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
 	int ret = 0;
 	size_t i;
 	EC_POINT *p=NULL;
+	EC_POINT *acc = NULL;
 
 	if (ctx == NULL)
 		{
@@ -338,15 +348,16 @@ int ec_GF2m_simple_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
 		}
 
 	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++)
@@ -354,13 +365,16 @@ int ec_GF2m_simple_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
 		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;
@@ -379,3 +393,5 @@ int ec_GF2m_have_precompute_mult(const EC_GROUP *group)
 	{
 	return ec_wNAF_have_precompute_mult(group);
  	}
+
+#endif