X-Git-Url: https://git.openssl.org/gitweb/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fec%2Fec2_mult.c;h=68cc8771d5ebfe1154c077f6316f52965e80b527;hp=a0effa95ad8ba93b95ba3d94afb8a95536bb8576;hb=4d2207f097ebd50d3f23568b013539930bbdf910;hpb=37c660ff9b22d6f0eb19a9881d3b663ca4f63449

diff --git a/crypto/ec/ec2_mult.c b/crypto/ec/ec2_mult.c
index a0effa95ad..68cc8771d5 100644
--- a/crypto/ec/ec2_mult.c
+++ b/crypto/ec/ec2_mult.c
@@ -21,7 +21,7 @@
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer. 
+ *    notice, this list of conditions and the following disclaimer.
  *
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in
@@ -71,309 +71,393 @@
 
 #include "ec_lcl.h"
 
+#ifndef OPENSSL_NO_EC2M
 
-/* Compute the x-coordinate x/z for the point 2*(x/z) in Montgomery projective 
+/*-
+ * Compute the x-coordinate x/z for the point 2*(x/z) in Montgomery projective
  * coordinates.
- * Uses algorithm Mdouble in appendix of 
- *     Lopez, J. and Dahab, R.  "Fast multiplication on elliptic curves over 
- *     GF(2^m) without precomputation".
+ * Uses algorithm Mdouble in appendix of
+ *     Lopez, J. and Dahab, R.  "Fast multiplication on elliptic curves over
+ *     GF(2^m) without precomputation" (CHES '99, LNCS 1717).
  * modified to not require precomputation of c=b^{2^{m-1}}.
  */
-static int gf2m_Mdouble(const EC_GROUP *group, BIGNUM *x, BIGNUM *z, BN_CTX *ctx)
-	{
-	BIGNUM *t1;
-	int ret = 0;
-	
-	/* Since Mdouble is static we can guarantee that ctx != NULL. */
-	BN_CTX_start(ctx);
-	t1 = BN_CTX_get(ctx);
-	if (t1 == NULL) goto err;
-
-	if (!group->meth->field_sqr(group, x, x, ctx)) goto err;
-	if (!group->meth->field_sqr(group, t1, z, ctx)) goto err;
-	if (!group->meth->field_mul(group, z, x, t1, ctx)) goto err;
-	if (!group->meth->field_sqr(group, x, x, ctx)) goto err;
-	if (!group->meth->field_sqr(group, t1, t1, ctx)) goto err;
-	if (!group->meth->field_mul(group, t1, &group->b, t1, ctx)) goto err;
-	if (!BN_GF2m_add(x, x, t1)) goto err;
-
-	ret = 1;
+static int gf2m_Mdouble(const EC_GROUP *group, BIGNUM *x, BIGNUM *z,
+                        BN_CTX *ctx)
+{
+    BIGNUM *t1;
+    int ret = 0;
+
+    /* Since Mdouble is static we can guarantee that ctx != NULL. */
+    BN_CTX_start(ctx);
+    t1 = BN_CTX_get(ctx);
+    if (t1 == NULL)
+        goto err;
+
+    if (!group->meth->field_sqr(group, x, x, ctx))
+        goto err;
+    if (!group->meth->field_sqr(group, t1, z, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, z, x, t1, ctx))
+        goto err;
+    if (!group->meth->field_sqr(group, x, x, ctx))
+        goto err;
+    if (!group->meth->field_sqr(group, t1, t1, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, t1, &group->b, t1, ctx))
+        goto err;
+    if (!BN_GF2m_add(x, x, t1))
+        goto err;
+
+    ret = 1;
 
  err:
-	BN_CTX_end(ctx);
-	return ret;
-	}
+    BN_CTX_end(ctx);
+    return ret;
+}
 
-/* Compute the x-coordinate x1/z1 for the point (x1/z1)+(x2/x2) in Montgomery 
+/*-
+ * Compute the x-coordinate x1/z1 for the point (x1/z1)+(x2/x2) in Montgomery
  * projective coordinates.
- * Uses algorithm Madd in appendix of 
- *     Lopex, J. and Dahab, R.  "Fast multiplication on elliptic curves over 
- *     GF(2^m) without precomputation".
+ * Uses algorithm Madd in appendix of
+ *     Lopez, J. and Dahab, R.  "Fast multiplication on elliptic curves over
+ *     GF(2^m) without precomputation" (CHES '99, LNCS 1717).
  */
-static int gf2m_Madd(const EC_GROUP *group, const BIGNUM *x, BIGNUM *x1, BIGNUM *z1, 
-	const BIGNUM *x2, const BIGNUM *z2, BN_CTX *ctx)
-	{
-	BIGNUM *t1, *t2;
-	int ret = 0;
-	
-	/* Since Madd is static we can guarantee that ctx != NULL. */
-	BN_CTX_start(ctx);
-	t1 = BN_CTX_get(ctx);
-	t2 = BN_CTX_get(ctx);
-	if (t2 == NULL) goto err;
-
-	if (!BN_copy(t1, x)) goto err;
-	if (!group->meth->field_mul(group, x1, x1, z2, ctx)) goto err;
-	if (!group->meth->field_mul(group, z1, z1, x2, ctx)) goto err;
-	if (!group->meth->field_mul(group, t2, x1, z1, ctx)) goto err;
-	if (!BN_GF2m_add(z1, z1, x1)) goto err;
-	if (!group->meth->field_sqr(group, z1, z1, ctx)) goto err;
-	if (!group->meth->field_mul(group, x1, z1, t1, ctx)) goto err;
-	if (!BN_GF2m_add(x1, x1, t2)) goto err;
-
-	ret = 1;
+static int gf2m_Madd(const EC_GROUP *group, const BIGNUM *x, BIGNUM *x1,
+                     BIGNUM *z1, const BIGNUM *x2, const BIGNUM *z2,
+                     BN_CTX *ctx)
+{
+    BIGNUM *t1, *t2;
+    int ret = 0;
+
+    /* Since Madd is static we can guarantee that ctx != NULL. */
+    BN_CTX_start(ctx);
+    t1 = BN_CTX_get(ctx);
+    t2 = BN_CTX_get(ctx);
+    if (t2 == NULL)
+        goto err;
+
+    if (!BN_copy(t1, x))
+        goto err;
+    if (!group->meth->field_mul(group, x1, x1, z2, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, z1, z1, x2, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, t2, x1, z1, ctx))
+        goto err;
+    if (!BN_GF2m_add(z1, z1, x1))
+        goto err;
+    if (!group->meth->field_sqr(group, z1, z1, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, x1, z1, t1, ctx))
+        goto err;
+    if (!BN_GF2m_add(x1, x1, t2))
+        goto err;
+
+    ret = 1;
 
  err:
-	BN_CTX_end(ctx);
-	return ret;
-	}
-
-/* Compute the x, y affine coordinates from the point (x1, z1) (x2, z2) 
- * using Montgomery point multiplication algorithm Mxy() in appendix of 
- *     Lopex, J. and Dahab, R.  "Fast multiplication on elliptic curves over 
- *     GF(2^m) without precomputation".
+    BN_CTX_end(ctx);
+    return ret;
+}
+
+/*-
+ * Compute the x, y affine coordinates from the point (x1, z1) (x2, z2)
+ * using Montgomery point multiplication algorithm Mxy() in appendix of
+ *     Lopez, J. and Dahab, R.  "Fast multiplication on elliptic curves over
+ *     GF(2^m) without precomputation" (CHES '99, LNCS 1717).
  * Returns:
  *     0 on error
  *     1 if return value should be the point at infinity
  *     2 otherwise
  */
-static int gf2m_Mxy(const EC_GROUP *group, const BIGNUM *x, const BIGNUM *y, BIGNUM *x1, 
-	BIGNUM *z1, BIGNUM *x2, BIGNUM *z2, BN_CTX *ctx)
-	{
-	BIGNUM *t3, *t4, *t5;
-	int ret = 0;
-	
-	if (BN_is_zero(z1))
-		{
-		if (!BN_zero(x2)) return 0;
-		if (!BN_zero(z2)) return 0;
-		return 1;
-		}
-	
-	if (BN_is_zero(z2))
-		{
-		if (!BN_copy(x2, x)) return 0;
-		if (!BN_GF2m_add(z2, x, y)) return 0;
-		return 2;
-		}
-		
-	/* Since Mxy is static we can guarantee that ctx != NULL. */
-	BN_CTX_start(ctx);
-	t3 = BN_CTX_get(ctx);
-	t4 = BN_CTX_get(ctx);
-	t5 = BN_CTX_get(ctx);
-	if (t5 == NULL) goto err;
-
-	if (!BN_one(t5)) goto err;
-
-	if (!group->meth->field_mul(group, t3, z1, z2, ctx)) goto err;
-
-	if (!group->meth->field_mul(group, z1, z1, x, ctx)) goto err;
-	if (!BN_GF2m_add(z1, z1, x1)) goto err;
-	if (!group->meth->field_mul(group, z2, z2, x, ctx)) goto err;
-	if (!group->meth->field_mul(group, x1, z2, x1, ctx)) goto err;
-	if (!BN_GF2m_add(z2, z2, x2)) goto err;
-
-	if (!group->meth->field_mul(group, z2, z2, z1, ctx)) goto err;
-	if (!group->meth->field_sqr(group, t4, x, ctx)) goto err;
-	if (!BN_GF2m_add(t4, t4, y)) goto err;
-	if (!group->meth->field_mul(group, t4, t4, t3, ctx)) goto err;
-	if (!BN_GF2m_add(t4, t4, z2)) goto err;
-
-	if (!group->meth->field_mul(group, t3, t3, x, ctx)) goto err;
-	if (!group->meth->field_div(group, t3, t5, t3, ctx)) goto err;
-	if (!group->meth->field_mul(group, t4, t3, t4, ctx)) goto err;
-	if (!group->meth->field_mul(group, x2, x1, t3, ctx)) goto err;
-	if (!BN_GF2m_add(z2, x2, x)) goto err;
-
-	if (!group->meth->field_mul(group, z2, z2, t4, ctx)) goto err;
-	if (!BN_GF2m_add(z2, z2, y)) goto err;
-
-	ret = 2;
+static int gf2m_Mxy(const EC_GROUP *group, const BIGNUM *x, const BIGNUM *y,
+                    BIGNUM *x1, BIGNUM *z1, BIGNUM *x2, BIGNUM *z2,
+                    BN_CTX *ctx)
+{
+    BIGNUM *t3, *t4, *t5;
+    int ret = 0;
+
+    if (BN_is_zero(z1)) {
+        BN_zero(x2);
+        BN_zero(z2);
+        return 1;
+    }
+
+    if (BN_is_zero(z2)) {
+        if (!BN_copy(x2, x))
+            return 0;
+        if (!BN_GF2m_add(z2, x, y))
+            return 0;
+        return 2;
+    }
+
+    /* Since Mxy is static we can guarantee that ctx != NULL. */
+    BN_CTX_start(ctx);
+    t3 = BN_CTX_get(ctx);
+    t4 = BN_CTX_get(ctx);
+    t5 = BN_CTX_get(ctx);
+    if (t5 == NULL)
+        goto err;
+
+    if (!BN_one(t5))
+        goto err;
+
+    if (!group->meth->field_mul(group, t3, z1, z2, ctx))
+        goto err;
+
+    if (!group->meth->field_mul(group, z1, z1, x, ctx))
+        goto err;
+    if (!BN_GF2m_add(z1, z1, x1))
+        goto err;
+    if (!group->meth->field_mul(group, z2, z2, x, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, x1, z2, x1, ctx))
+        goto err;
+    if (!BN_GF2m_add(z2, z2, x2))
+        goto err;
+
+    if (!group->meth->field_mul(group, z2, z2, z1, ctx))
+        goto err;
+    if (!group->meth->field_sqr(group, t4, x, ctx))
+        goto err;
+    if (!BN_GF2m_add(t4, t4, y))
+        goto err;
+    if (!group->meth->field_mul(group, t4, t4, t3, ctx))
+        goto err;
+    if (!BN_GF2m_add(t4, t4, z2))
+        goto err;
+
+    if (!group->meth->field_mul(group, t3, t3, x, ctx))
+        goto err;
+    if (!group->meth->field_div(group, t3, t5, t3, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, t4, t3, t4, ctx))
+        goto err;
+    if (!group->meth->field_mul(group, x2, x1, t3, ctx))
+        goto err;
+    if (!BN_GF2m_add(z2, x2, x))
+        goto err;
+
+    if (!group->meth->field_mul(group, z2, z2, t4, ctx))
+        goto err;
+    if (!BN_GF2m_add(z2, z2, y))
+        goto err;
+
+    ret = 2;
 
  err:
-	BN_CTX_end(ctx);
-	return ret;
-	}
+    BN_CTX_end(ctx);
+    return ret;
+}
 
-/* Computes scalar*point and stores the result in r.
+/*-
+ * Computes scalar*point and stores the result in r.
  * point can not equal r.
- * Uses algorithm 2P of
- *     Lopex, J. and Dahab, R.  "Fast multiplication on elliptic curves over 
- *     GF(2^m) without precomputation".
+ * 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)
-	{
-	BIGNUM *x1, *x2, *z1, *z2;
-	int ret = 0, i, j;
-	BN_ULONG mask;
-
-	if (r == point)
-		{
-		ECerr(EC_F_EC_POINT_MUL, EC_R_INVALID_ARGUMENT);
-		return 0;
-		}
-	
-	/* if result should be point at infinity */
-	if ((scalar == NULL) || BN_is_zero(scalar) || (point == NULL) || 
-		EC_POINT_is_at_infinity(group, point))
-		{
-		return EC_POINT_set_to_infinity(group, r);
-		}
-
-	/* only support affine coordinates */
-	if (!point->Z_is_one) return 0;
-
-	/* Since point_multiply is static we can guarantee that ctx != NULL. */
-	BN_CTX_start(ctx);
-	x1 = BN_CTX_get(ctx);
-	z1 = BN_CTX_get(ctx);
-	if (z1 == NULL) goto err;
-
-	x2 = &r->X;
-	z2 = &r->Y;
-
-	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 */
-	if (!group->meth->field_sqr(group, x2, z2, ctx)) goto err;
-	if (!BN_GF2m_add(x2, x2, &group->b)) goto err; /* x2 = x^4 + b */
-
-	/* find top most bit and go one past it */
-	i = scalar->top - 1; j = BN_BITS2 - 1;
-	mask = BN_TBIT;
-	while (!(scalar->d[i] & mask)) { mask >>= 1; j--; }
-	mask >>= 1; j--;
-	/* if top most bit was at word break, go to next word */
-	if (!mask) 
-		{
-		i--; j = BN_BITS2 - 1;
-		mask = BN_TBIT;
-		}
-
-	for (; i >= 0; i--)
-		{
-		for (; j >= 0; j--)
-			{
-			if (scalar->d[i] & 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;
-				}
-			mask >>= 1;
-			}
-		j = BN_BITS2 - 1;
-		mask = BN_TBIT;
-		}
-
-	/* convert out of "projective" coordinates */
-	i = gf2m_Mxy(group, &point->X, &point->Y, x1, z1, x2, z2, ctx);
-	if (i == 0) goto err;
-	else if (i == 1) 
-		{
-		if (!EC_POINT_set_to_infinity(group, r)) goto err;
-		}
-	else
-		{
-		if (!BN_one(&r->Z)) goto err;
-		r->Z_is_one = 1;
-		}
-
-	/* GF(2^m) field elements should always have BIGNUM::neg = 0 */
-	BN_set_sign(&r->X, 0);
-	BN_set_sign(&r->Y, 0);
-
-	ret = 1;
+static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group,
+                                             EC_POINT *r,
+                                             const BIGNUM *scalar,
+                                             const EC_POINT *point,
+                                             BN_CTX *ctx)
+{
+    BIGNUM *x1, *x2, *z1, *z2;
+    int ret = 0, i;
+    BN_ULONG mask, word;
+
+    if (r == point) {
+        ECerr(EC_F_EC_GF2M_MONTGOMERY_POINT_MULTIPLY, EC_R_INVALID_ARGUMENT);
+        return 0;
+    }
+
+    /* if result should be point at infinity */
+    if ((scalar == NULL) || BN_is_zero(scalar) || (point == NULL) ||
+        EC_POINT_is_at_infinity(group, point)) {
+        return EC_POINT_set_to_infinity(group, r);
+    }
+
+    /* only support affine coordinates */
+    if (!point->Z_is_one)
+        return 0;
+
+    /*
+     * Since point_multiply is static we can guarantee that ctx != NULL.
+     */
+    BN_CTX_start(ctx);
+    x1 = BN_CTX_get(ctx);
+    z1 = BN_CTX_get(ctx);
+    if (z1 == NULL)
+        goto err;
+
+    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 */
+    if (!group->meth->field_sqr(group, x2, z2, ctx))
+        goto err;
+    if (!BN_GF2m_add(x2, x2, &group->b))
+        goto err;               /* x2 = x^4 + b */
+
+    /* find top most bit and go one past it */
+    i = scalar->top - 1;
+    mask = BN_TBIT;
+    word = scalar->d[i];
+    while (!(word & mask))
+        mask >>= 1;
+    mask >>= 1;
+    /* if top most bit was at word break, go to next word */
+    if (!mask) {
+        i--;
+        mask = BN_TBIT;
+    }
+
+    for (; i >= 0; i--) {
+        word = scalar->d[i];
+        while (mask) {
+            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;
+    }
+
+    /* convert out of "projective" coordinates */
+    i = gf2m_Mxy(group, &point->X, &point->Y, x1, z1, x2, z2, ctx);
+    if (i == 0)
+        goto err;
+    else if (i == 1) {
+        if (!EC_POINT_set_to_infinity(group, r))
+            goto err;
+    } else {
+        if (!BN_one(&r->Z))
+            goto err;
+        r->Z_is_one = 1;
+    }
+
+    /* GF(2^m) field elements should always have BIGNUM::neg = 0 */
+    BN_set_negative(&r->X, 0);
+    BN_set_negative(&r->Y, 0);
+
+    ret = 1;
 
  err:
-	BN_CTX_end(ctx);
-	return ret;
-	}
-
+    BN_CTX_end(ctx);
+    return ret;
+}
 
-/* Computes the sum
+/*-
+ * Computes the sum
  *     scalar*group->generator + scalars[0]*points[0] + ... + scalars[num-1]*points[num-1]
  * gracefully ignoring NULL scalar values.
  */
-int ec_GF2m_simple_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
-	size_t num, const EC_POINT *points[], const BIGNUM *scalars[], BN_CTX *ctx)
-	{
-	BN_CTX *new_ctx = NULL;
-	int ret = 0, i;
-	EC_POINT *p=NULL;
-
-	if (ctx == NULL)
-		{
-		ctx = new_ctx = BN_CTX_new();
-		if (ctx == NULL)
-			return 0;
-		}
-
-	/* This implementation is more efficient than the wNAF implementation for 2
-	 * or fewer points.  Use the ec_wNAF_mul implementation for 3 or more points,
-	 * or if we can perform a fast multiplication based on precomputation.
-	 */
-	if ((scalar && (num > 1)) || (num > 2) || (num == 0 && EC_GROUP_have_precompute_mult(group)))
-		{
-		ret = ec_wNAF_mul(group, r, scalar, num, points, scalars, ctx);
-		goto err;
-		}
-
-	if ((p = EC_POINT_new(group)) == NULL) goto err;
-
-	if (!EC_POINT_set_to_infinity(group, r)) goto err;
-
-	if (scalar)
-		{
-		if (!ec_GF2m_montgomery_point_multiply(group, p, scalar, group->generator, ctx)) goto err;
-		if (BN_get_sign(scalar)) 
-			if (!group->meth->invert(group, p, ctx)) goto err;
-		if (!group->meth->add(group, r, r, 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_get_sign(scalars[i]))
-			if (!group->meth->invert(group, p, ctx)) goto err;
-		if (!group->meth->add(group, r, r, p, ctx)) goto err;
-		}
-
-	ret = 1;
-
-  err:
-	if (p) EC_POINT_free(p);
-	if (new_ctx != NULL)
-		BN_CTX_free(new_ctx);
-	return ret;
-	}
-
-
-/* Precomputation for point multiplication: fall back to wNAF methods
- * because ec_GF2m_simple_mul() uses ec_wNAF_mul() if appropriate */
+int ec_GF2m_simple_mul(const EC_GROUP *group, EC_POINT *r,
+                       const BIGNUM *scalar, size_t num,
+                       const EC_POINT *points[], const BIGNUM *scalars[],
+                       BN_CTX *ctx)
+{
+    BN_CTX *new_ctx = NULL;
+    int ret = 0;
+    size_t i;
+    EC_POINT *p = NULL;
+    EC_POINT *acc = NULL;
+
+    if (ctx == NULL) {
+        ctx = new_ctx = BN_CTX_new();
+        if (ctx == NULL)
+            return 0;
+    }
+
+    /*
+     * This implementation is more efficient than the wNAF implementation for
+     * 2 or fewer points.  Use the ec_wNAF_mul implementation for 3 or more
+     * points, or if we can perform a fast multiplication based on
+     * precomputation.
+     */
+    if ((scalar && (num > 1)) || (num > 2)
+        || (num == 0 && EC_GROUP_have_precompute_mult(group))) {
+        ret = ec_wNAF_mul(group, r, scalar, num, points, scalars, ctx);
+        goto err;
+    }
+
+    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, 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 (!group->meth->invert(group, 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, 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;
+}
+
+/*
+ * Precomputation for point multiplication: fall back to wNAF methods because
+ * ec_GF2m_simple_mul() uses ec_wNAF_mul() if appropriate
+ */
 
 int ec_GF2m_precompute_mult(EC_GROUP *group, BN_CTX *ctx)
-	{
-	return ec_wNAF_precompute_mult(group, ctx);
- 	}
+{
+    return ec_wNAF_precompute_mult(group, ctx);
+}
 
 int ec_GF2m_have_precompute_mult(const EC_GROUP *group)
-	{
-	return ec_wNAF_have_precompute_mult(group);
- 	}
+{
+    return ec_wNAF_have_precompute_mult(group);
+}
+
+#endif