From: Dr. Stephen Henson <steve@openssl.org>
Date: Wed, 25 May 2011 14:43:47 +0000 (+0000)
Subject: Fix the ECDSA timing attack mentioned in the paper at:
X-Git-Tag: OpenSSL_0_9_8s~54
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=1e368ab08fccdb824cb91bd7765880de0dbf2ea8;p=oweals%2Fopenssl.git

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.
---

diff --git a/CHANGES b/CHANGES
index 43299af8ec..a3ee3b0bc6 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,7 +4,12 @@
 
  Changes between 0.9.8r and 0.9.8s [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]
 
  Changes between 0.9.8q and 0.9.8r [8 Feb 2011]
 
diff --git a/crypto/ecdsa/ecs_ossl.c b/crypto/ecdsa/ecs_ossl.c
index 551cf5068f..bbb5588cbe 100644
--- a/crypto/ecdsa/ecs_ossl.c
+++ b/crypto/ecdsa/ecs_ossl.c
@@ -144,6 +144,16 @@ 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))
 		{