Reserve option to use BN_mod_exp_mont_consttime in ECDSA.

Submitted by Shay Gueron, Intel Corp.
RT: 3149

Reviewed-by: Rich Salz <rsalz@openssl.org>

1 files changed, 71 insertions, 0 deletions

diff --git a/crypto/ec/ec_lib.c b/crypto/ec/ec_lib.c
index a295a84f2b..0a182d4229 100644
--- a/crypto/ec/ec_lib.c
+++ b/crypto/ec/ec_lib.c
@@ -101,6 +101,7 @@ EC_GROUP *EC_GROUP_new(const EC_METHOD *meth)
 	ret->meth = meth;
 
 	ret->extra_data = NULL;
+	ret->mont_data = NULL;
 
 	ret->generator = NULL;
 	BN_init(&ret->order);
@@ -132,6 +133,9 @@ void EC_GROUP_free(EC_GROUP *group)
 
 	EC_EX_DATA_free_all_data(&group->extra_data);
 
+	if (group->mont_data)
+		BN_MONT_CTX_free(group->mont_data);
+
 	if (group->generator != NULL)
 		EC_POINT_free(group->generator);
 	BN_free(&group->order);
@@ -155,6 +159,9 @@ void EC_GROUP_clear_free(EC_GROUP *group)
 
 	EC_EX_DATA_clear_free_all_data(&group->extra_data);
 
+	if (group->mont_data)
+		BN_MONT_CTX_free(group->mont_data);
+
 	if (group->generator != NULL)
 		EC_POINT_clear_free(group->generator);
 	BN_clear_free(&group->order);
@@ -200,6 +207,25 @@ int EC_GROUP_copy(EC_GROUP *dest, const EC_GROUP *src)
 			return 0;
 		}
 
+	if (src->mont_data != NULL)
+		{
+		if (dest->mont_data == NULL)
+			{
+			dest->mont_data = BN_MONT_CTX_new();
+			if (dest->mont_data == NULL) return 0;
+			}
+		if (!BN_MONT_CTX_copy(dest->mont_data, src->mont_data)) return 0;
+		}
+	else
+		{
+		/* src->generator == NULL */
+		if (dest->mont_data != NULL)
+			{
+			BN_MONT_CTX_free(dest->mont_data);
+			dest->mont_data = NULL;
+			}
+		}
+
 	if (src->generator != NULL)
 		{
 		if (dest->generator == NULL)
@@ -309,6 +335,11 @@ int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, const BIG
 	else
 		BN_zero(&group->cofactor);
 
+	/* We ignore the return value because some groups have an order with
+	 * factors of two, which makes the Montgomery setup fail.
+	 * |group->mont_data| will be NULL in this case. */
+	ec_precompute_mont_data(group);
+
 	return 1;
 	}
 
@@ -318,6 +349,10 @@ const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group)
 	return group->generator;
 	}
 
+BN_MONT_CTX *EC_GROUP_get_mont_data(const EC_GROUP *group)
+	{
+	return group->mont_data;
+	}
 
 int EC_GROUP_get_order(const EC_GROUP *group, BIGNUM *order, BN_CTX *ctx)
 	{
@@ -1097,3 +1132,39 @@ int EC_GROUP_have_precompute_mult(const EC_GROUP *group)
 	else
 		return 0; /* cannot tell whether precomputation has been performed */
 	}
+
+/* ec_precompute_mont_data sets |group->mont_data| from |group->order| and
+ * returns one on success. On error it returns zero. */
+int ec_precompute_mont_data(EC_GROUP *group)
+	{
+	BN_CTX *ctx = BN_CTX_new();
+	int ret = 0;
+
+	if (group->mont_data)
+		{
+		BN_MONT_CTX_free(group->mont_data);
+		group->mont_data = NULL;
+		}
+
+	if (ctx == NULL)
+		goto err;
+
+	group->mont_data = BN_MONT_CTX_new();
+	if (!group->mont_data)
+		goto err;
+
+	if (!BN_MONT_CTX_set(group->mont_data, &group->order, ctx))
+		{
+		BN_MONT_CTX_free(group->mont_data);
+		group->mont_data = NULL;
+		goto err;
+		}
+
+	ret = 1;
+
+err:
+
+	if (ctx)
+		BN_CTX_free(ctx);
+	return ret;
+	}