Fix the ECDSA timing attack mentioned in the paper at:

http://eprint.iacr.org/2011/232.pdf

Thanks to the original authors Billy Bob Brumley and Nicola Tuveri for
bringing this to our attention.

CHANGES

@@ -4,6 +4,13 @@
 
  Changes between 1.0.1 and 1.1.0  [xx XXX xxxx]
 
+  *) Add protection against ECDSA timing attacks as mentioned in the paper
+     by Billy Bob Brumley and Nicola Tuveri, see:
+
+	http://eprint.iacr.org/2011/232.pdf
+
+     [Billy Bob Brumley and Nicola Tuveri]
+
   *) Add TLS v1.2 server support for client authentication. 
      [Steve Henson]
 

crypto/ecdsa/ecs_ossl.c

@@ -151,6 +151,16 @@ static int ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp,
 			}
 		while (BN_is_zero(k));
 
+#ifdef ECDSA_POINT_MUL_NO_CONSTTIME
+		/* We do not want timing information to leak the length of k,
+		 * so we compute G*k using an equivalent scalar of fixed
+		 * bit-length. */
+
+		if (!BN_add(k, k, order)) goto err;
+		if (BN_num_bits(k) <= BN_num_bits(order))
+			if (!BN_add(k, k, order)) goto err;
+#endif /* def(ECDSA_POINT_MUL_NO_CONSTTIME) */
+
 		/* compute r the x-coordinate of generator * k */
 		if (!EC_POINT_mul(group, tmp_point, k, NULL, NULL, ctx))
 		{