Timing vulnerability in ECDSA signature generation (CVE-2018-0735)
authorPauli <paul.dale@oracle.com>
Fri, 26 Oct 2018 00:54:58 +0000 (10:54 +1000)
committerPauli <paul.dale@oracle.com>
Sun, 28 Oct 2018 22:05:06 +0000 (08:05 +1000)
Preallocate an extra limb for some of the big numbers to avoid a reallocation
that can potentially provide a side channel.

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/7486)

(cherry picked from commit 99540ec79491f59ed8b46b4edf130e17dc907f52)

crypto/ec/ec_mult.c

index 22bb30f..ff882cc 100644 (file)
@@ -177,8 +177,8 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r,
      */
     cardinality_bits = BN_num_bits(cardinality);
     group_top = bn_get_top(cardinality);
-    if ((bn_wexpand(k, group_top + 1) == NULL)
-        || (bn_wexpand(lambda, group_top + 1) == NULL))
+    if ((bn_wexpand(k, group_top + 2) == NULL)
+        || (bn_wexpand(lambda, group_top + 2) == NULL)) {
         goto err;
 
     if (!BN_copy(k, scalar))
@@ -205,7 +205,7 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r,
      * k := scalar + 2*cardinality
      */
     kbit = BN_is_bit_set(lambda, cardinality_bits);
-    BN_consttime_swap(kbit, k, lambda, group_top + 1);
+    BN_consttime_swap(kbit, k, lambda, group_top + 2);
 
     group_top = bn_get_top(group->field);
     if ((bn_wexpand(s->X, group_top) == NULL)