Implement fixed-window exponentiation to mitigate hyper-threading

timing attacks.

BN_FLG_EXP_CONSTTIME requests this algorithm, and this done by default for
RSA/DSA/DH private key computations unless
RSA_FLAG_NO_EXP_CONSTTIME/DSA_FLAG_NO_EXP_CONSTTIME/
DH_FLAG_NO_EXP_CONSTTIME is set.

Submitted by: Matthew D Wood
Reviewed by: Bodo Moeller

1 files changed, 118 insertions, 9 deletions

diff --git a/crypto/rsa/rsa_eay.c b/crypto/rsa/rsa_eay.c
index 21755c0..175ab8a 100644
--- a/crypto/rsa/rsa_eay.c
+++ b/crypto/rsa/rsa_eay.c
@@ -55,6 +55,59 @@
  * copied and put under another distribution licence
  * [including the GNU Public Licence.]
  */
+/* ====================================================================
+ * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    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
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. All advertising materials mentioning features or use of this
+ *    software must display the following acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
+ *
+ * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please contact
+ *    openssl-core@openssl.org.
+ *
+ * 5. Products derived from this software may not be called "OpenSSL"
+ *    nor may "OpenSSL" appear in their names without prior written
+ *    permission of the OpenSSL Project.
+ *
+ * 6. Redistributions of any form whatsoever must retain the following
+ *    acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
+ * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This product includes cryptographic software written by Eric Young
+ * (eay@cryptsoft.com).  This product includes software written by Tim
+ * Hudson (tjh@cryptsoft.com).
+ *
+ */
 
 #include <stdio.h>
 #include "cryptlib.h"
@@ -320,11 +373,25 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 		(rsa->dmp1 != NULL) &&
 		(rsa->dmq1 != NULL) &&
 		(rsa->iqmp != NULL)) )
-		{ if (!rsa->meth->rsa_mod_exp(ret,f,rsa,ctx)) goto err; }
+		{ 
+		if (!rsa->meth->rsa_mod_exp(ret, f, rsa, ctx)) goto err;
+		}
 	else
 		{
+		BIGNUM local_d;
+		BIGNUM *d = NULL;
+		
+		if (!(rsa->flags & RSA_FLAG_NO_EXP_CONSTTIME))
+			{
+			d = &local_d;
+			BN_with_flags(d, rsa->d, BN_FLG_EXP_CONSTTIME);
+			}
+		else
+			d = rsa->d;
+
 		MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PUBLIC, goto err);
-		if (!rsa->meth->bn_mod_exp(ret,f,rsa->d,rsa->n,ctx,
+
+		if (!rsa->meth->bn_mod_exp(ret,f,d,rsa->n,ctx,
 				rsa->_method_mod_n)) goto err;
 		}
 
@@ -416,13 +483,26 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
 		(rsa->dmp1 != NULL) &&
 		(rsa->dmq1 != NULL) &&
 		(rsa->iqmp != NULL)) )
-		{ if (!rsa->meth->rsa_mod_exp(ret,f,rsa,ctx)) goto err; }
+		{
+		if (!rsa->meth->rsa_mod_exp(ret, f, rsa, ctx)) goto err;
+		}
 	else
 		{
+		BIGNUM local_d;
+		BIGNUM *d = NULL;
+		
+		if (!(rsa->flags & RSA_FLAG_NO_EXP_CONSTTIME))
+			{
+			d = &local_d;
+			BN_with_flags(d, rsa->d, BN_FLG_EXP_CONSTTIME);
+			}
+		else
+			d = rsa->d;
+
 		MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PUBLIC, goto err);
-		if (!rsa->meth->bn_mod_exp(ret,f,rsa->d,rsa->n,ctx,
+		if (!rsa->meth->bn_mod_exp(ret,f,d,rsa->n,ctx,
 				rsa->_method_mod_n))
-			goto err;
+		  goto err;
 		}
 
 	if (blinding)
@@ -547,6 +627,8 @@ err:
 static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa, BN_CTX *ctx)
 	{
 	BIGNUM *r1,*m1,*vrfy;
+	BIGNUM local_dmp1, local_dmq1;
+	BIGNUM *dmp1, *dmq1;
 	int ret=0;
 
 	BN_CTX_start(ctx);
@@ -559,11 +641,25 @@ static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa, BN_CTX *ctx)
 	MONT_HELPER(rsa, ctx, n, rsa->flags & RSA_FLAG_CACHE_PUBLIC, goto err);
 
 	if (!BN_mod(r1,I,rsa->q,ctx)) goto err;
-	if (!rsa->meth->bn_mod_exp(m1,r1,rsa->dmq1,rsa->q,ctx,
+	if (!(rsa->flags & RSA_FLAG_NO_EXP_CONSTTIME))
+		{
+		dmq1 = &local_dmq1;
+		BN_with_flags(dmq1, rsa->dmq1, BN_FLG_EXP_CONSTTIME);
+		}
+	else
+		dmq1 = rsa->dmq1;
+	if (!rsa->meth->bn_mod_exp(m1,r1,dmq1,rsa->q,ctx,
 		rsa->_method_mod_q)) goto err;
 
 	if (!BN_mod(r1,I,rsa->p,ctx)) goto err;
-	if (!rsa->meth->bn_mod_exp(r0,r1,rsa->dmp1,rsa->p,ctx,
+	if (!(rsa->flags & RSA_FLAG_NO_EXP_CONSTTIME))
+		{
+		dmp1 = &local_dmp1;
+		BN_with_flags(dmp1, rsa->dmp1, BN_FLG_EXP_CONSTTIME);
+		}
+	else
+		dmp1 = rsa->dmp1;
+	if (!rsa->meth->bn_mod_exp(r0,r1,dmp1,rsa->p,ctx,
 		rsa->_method_mod_p)) goto err;
 
 	if (!BN_sub(r0,r0,m1)) goto err;
@@ -598,11 +694,24 @@ static int RSA_eay_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa, BN_CTX *ctx)
 		if (BN_is_negative(vrfy))
 			if (!BN_add(vrfy, vrfy, rsa->n)) goto err;
 		if (!BN_is_zero(vrfy))
+			{
 			/* 'I' and 'vrfy' aren't congruent mod n. Don't leak
 			 * miscalculated CRT output, just do a raw (slower)
 			 * mod_exp and return that instead. */
-			if (!rsa->meth->bn_mod_exp(r0,I,rsa->d,rsa->n,ctx,
-					rsa->_method_mod_n)) goto err;
+
+			BIGNUM local_d;
+			BIGNUM *d = NULL;
+		
+			if (!(rsa->flags & RSA_FLAG_NO_EXP_CONSTTIME))
+				{
+				d = &local_d;
+				BN_with_flags(d, rsa->d, BN_FLG_EXP_CONSTTIME);
+				}
+			else
+				d = rsa->d;
+			if (!rsa->meth->bn_mod_exp(r0,I,d,rsa->n,ctx,
+						   rsa->_method_mod_n)) goto err;
+			}
 		}
 	ret=1;
 err: