Constant-time utilities

Pull constant-time methods out to a separate header, add tests.

Reviewed-by: Bodo Moeller <bodo@openssl.org>
(cherry picked from commit 73729e4cf3961e36b5534d270c11ff7cd811aa43)

Conflicts:
	ssl/Makefile
	test/Makefile

2 files changed, 32 insertions, 67 deletions

diff --git a/ssl/Makefile b/ssl/Makefile
index 90b9b9d44b..b82d38165c 100644
--- a/ssl/Makefile
+++ b/ssl/Makefile
@@ -545,27 +545,28 @@ s3_both.o: ../include/openssl/ssl23.h ../include/openssl/ssl3.h
 s3_both.o: ../include/openssl/stack.h ../include/openssl/symhacks.h
 s3_both.o: ../include/openssl/tls1.h ../include/openssl/x509.h
 s3_both.o: ../include/openssl/x509_vfy.h s3_both.c ssl_locl.h
-s3_cbc.o: ../e_os.h ../include/openssl/asn1.h ../include/openssl/bio.h
-s3_cbc.o: ../include/openssl/bn.h ../include/openssl/buffer.h
-s3_cbc.o: ../include/openssl/comp.h ../include/openssl/crypto.h
-s3_cbc.o: ../include/openssl/dsa.h ../include/openssl/dtls1.h
-s3_cbc.o: ../include/openssl/e_os2.h ../include/openssl/ec.h
-s3_cbc.o: ../include/openssl/ecdh.h ../include/openssl/ecdsa.h
-s3_cbc.o: ../include/openssl/err.h ../include/openssl/evp.h
-s3_cbc.o: ../include/openssl/fips.h ../include/openssl/hmac.h
-s3_cbc.o: ../include/openssl/kssl.h ../include/openssl/lhash.h
-s3_cbc.o: ../include/openssl/md5.h ../include/openssl/obj_mac.h
-s3_cbc.o: ../include/openssl/objects.h ../include/openssl/opensslconf.h
-s3_cbc.o: ../include/openssl/opensslv.h ../include/openssl/ossl_typ.h
-s3_cbc.o: ../include/openssl/pem.h ../include/openssl/pem2.h
-s3_cbc.o: ../include/openssl/pkcs7.h ../include/openssl/pq_compat.h
-s3_cbc.o: ../include/openssl/pqueue.h ../include/openssl/rsa.h
-s3_cbc.o: ../include/openssl/safestack.h ../include/openssl/sha.h
-s3_cbc.o: ../include/openssl/ssl.h ../include/openssl/ssl2.h
-s3_cbc.o: ../include/openssl/ssl23.h ../include/openssl/ssl3.h
-s3_cbc.o: ../include/openssl/stack.h ../include/openssl/symhacks.h
-s3_cbc.o: ../include/openssl/tls1.h ../include/openssl/x509.h
-s3_cbc.o: ../include/openssl/x509_vfy.h s3_cbc.c ssl_locl.h
+s3_cbc.o: ../crypto/constant_time_locl.h ../e_os.h ../include/openssl/asn1.h
+s3_cbc.o: ../include/openssl/bio.h ../include/openssl/bn.h
+s3_cbc.o: ../include/openssl/buffer.h ../include/openssl/comp.h
+s3_cbc.o: ../include/openssl/crypto.h ../include/openssl/dsa.h
+s3_cbc.o: ../include/openssl/dtls1.h ../include/openssl/e_os2.h
+s3_cbc.o: ../include/openssl/ec.h ../include/openssl/ecdh.h
+s3_cbc.o: ../include/openssl/ecdsa.h ../include/openssl/err.h
+s3_cbc.o: ../include/openssl/evp.h ../include/openssl/fips.h
+s3_cbc.o: ../include/openssl/hmac.h ../include/openssl/kssl.h
+s3_cbc.o: ../include/openssl/lhash.h ../include/openssl/md5.h
+s3_cbc.o: ../include/openssl/obj_mac.h ../include/openssl/objects.h
+s3_cbc.o: ../include/openssl/opensslconf.h ../include/openssl/opensslv.h
+s3_cbc.o: ../include/openssl/ossl_typ.h ../include/openssl/pem.h
+s3_cbc.o: ../include/openssl/pem2.h ../include/openssl/pkcs7.h
+s3_cbc.o: ../include/openssl/pq_compat.h ../include/openssl/pqueue.h
+s3_cbc.o: ../include/openssl/rsa.h ../include/openssl/safestack.h
+s3_cbc.o: ../include/openssl/sha.h ../include/openssl/ssl.h
+s3_cbc.o: ../include/openssl/ssl2.h ../include/openssl/ssl23.h
+s3_cbc.o: ../include/openssl/ssl3.h ../include/openssl/stack.h
+s3_cbc.o: ../include/openssl/symhacks.h ../include/openssl/tls1.h
+s3_cbc.o: ../include/openssl/x509.h ../include/openssl/x509_vfy.h s3_cbc.c
+s3_cbc.o: ssl_locl.h
 s3_clnt.o: ../e_os.h ../include/openssl/asn1.h ../include/openssl/bio.h
 s3_clnt.o: ../include/openssl/bn.h ../include/openssl/buffer.h
 s3_clnt.o: ../include/openssl/comp.h ../include/openssl/crypto.h
diff --git a/ssl/s3_cbc.c b/ssl/s3_cbc.c
index 9f57fc9a62..f7eaf94e50 100644
--- a/ssl/s3_cbc.c
+++ b/ssl/s3_cbc.c
@@ -53,6 +53,7 @@
  *
  */
 
+#include "../crypto/constant_time_locl.h"
 #include "ssl_locl.h"
 
 #include <openssl/md5.h>
@@ -67,37 +68,6 @@
  * supported by TLS.) */
 #define MAX_HASH_BLOCK_SIZE 128
 
-/* Some utility functions are needed:
- *
- * These macros return the given value with the MSB copied to all the other
- * bits. They use the fact that arithmetic shift shifts-in the sign bit.
- * However, this is not ensured by the C standard so you may need to replace
- * them with something else on odd CPUs. */
-#define DUPLICATE_MSB_TO_ALL(x) ( (unsigned)( (int)(x) >> (sizeof(int)*8-1) ) )
-#define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned char)(DUPLICATE_MSB_TO_ALL(x)))
-
-/* constant_time_lt returns 0xff if a<b and 0x00 otherwise. */
-static unsigned constant_time_lt(unsigned a, unsigned b)
-	{
-	a -= b;
-	return DUPLICATE_MSB_TO_ALL(a);
-	}
-
-/* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */
-static unsigned constant_time_ge(unsigned a, unsigned b)
-	{
-	a -= b;
-	return DUPLICATE_MSB_TO_ALL(~a);
-	}
-
-/* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
-static unsigned char constant_time_eq_8(unsigned a, unsigned b)
-	{
-	unsigned c = a ^ b;
-	c--;
-	return DUPLICATE_MSB_TO_ALL_8(c);
-	}
-
 /* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
  * record in |rec| by updating |rec->length| in constant time.
  *
@@ -127,7 +97,7 @@ int ssl3_cbc_remove_padding(const SSL* s,
 	rec->length -= padding_length;
 	rec->type |= padding_length<<8;	/* kludge: pass padding length */
 	return (int)((good & 1) | (~good & -1));
-}
+	}
 
 /* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
  * record in |rec| in constant time and returns 1 if the padding is valid and
@@ -201,7 +171,7 @@ int tls1_cbc_remove_padding(const SSL* s,
 
 	for (i = 0; i < to_check; i++)
 		{
-		unsigned char mask = constant_time_ge(padding_length, i);
+		unsigned char mask = constant_time_ge_8(padding_length, i);
 		unsigned char b = rec->data[rec->length-1-i];
 		/* The final |padding_length+1| bytes should all have the value
 		 * |padding_length|. Therefore the XOR should be zero. */
@@ -209,15 +179,9 @@ int tls1_cbc_remove_padding(const SSL* s,
 		}
 
 	/* If any of the final |padding_length+1| bytes had the wrong value,
-	 * one or more of the lower eight bits of |good| will be cleared. We
-	 * AND the bottom 8 bits together and duplicate the result to all the
-	 * bits. */
-	good &= good >> 4;
-	good &= good >> 2;
-	good &= good >> 1;
-	good <<= sizeof(good)*8-1;
-	good = DUPLICATE_MSB_TO_ALL(good);
-
+	 * one or more of the lower eight bits of |good| will be cleared.
+	 */
+	good = constant_time_eq(0xff, good & 0xff);
 	padding_length = good & (padding_length+1);
 	rec->length -= padding_length;
 	rec->type |= padding_length<<8;	/* kludge: pass padding length */
@@ -289,8 +253,8 @@ void ssl3_cbc_copy_mac(unsigned char* out,
 	memset(rotated_mac, 0, md_size);
 	for (i = scan_start, j = 0; i < orig_len; i++)
 		{
-		unsigned char mac_started = constant_time_ge(i, mac_start);
-		unsigned char mac_ended = constant_time_ge(i, mac_end);
+		unsigned char mac_started = constant_time_ge_8(i, mac_start);
+		unsigned char mac_ended = constant_time_ge_8(i, mac_end);
 		unsigned char b = rec->data[i];
 		rotated_mac[j++] |= b & mac_started & ~mac_ended;
 		j &= constant_time_lt(j,md_size);
@@ -676,8 +640,8 @@ void ssl3_cbc_digest_record(
 				b = data[k-header_length];
 			k++;
 
-			is_past_c = is_block_a & constant_time_ge(j, c);
-			is_past_cp1 = is_block_a & constant_time_ge(j, c+1);
+			is_past_c = is_block_a & constant_time_ge_8(j, c);
+			is_past_cp1 = is_block_a & constant_time_ge_8(j, c+1);
 			/* If this is the block containing the end of the
 			 * application data, and we are at the offset for the
 			 * 0x80 value, then overwrite b with 0x80. */