*
*/
+#include "../crypto/constant_time_locl.h"
#include "ssl_locl.h"
#include <openssl/md5.h>
* 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
+/*-
+ * ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
* record in |rec| by updating |rec->length| in constant time.
*
* block_size: the block size of the cipher used to encrypt the record.
* returns:
* 0: (in non-constant time) if the record is publicly invalid.
* 1: if the padding was valid
- * -1: otherwise. */
+ * -1: otherwise.
+ */
int ssl3_cbc_remove_padding(const SSL* s,
SSL3_RECORD *rec,
unsigned block_size,
padding_length = good & (padding_length+1);
rec->length -= padding_length;
rec->type |= padding_length<<8; /* kludge: pass padding length */
- return (int)((good & 1) | (~good & -1));
-}
+ return constant_time_select_int(good, 1, -1);
+ }
-/* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
+/*-
+ * 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
* -1 otherwise. It also removes any explicit IV from the start of the record
* without leaking any timing about whether there was enough space after the
* returns:
* 0: (in non-constant time) if the record is publicly invalid.
* 1: if the padding was valid
- * -1: otherwise. */
+ * -1: otherwise.
+ */
int tls1_cbc_remove_padding(const SSL* s,
SSL3_RECORD *rec,
unsigned block_size,
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. */
}
/* 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 */
- return (int)((good & 1) | (~good & -1));
+ return constant_time_select_int(good, 1, -1);
}
-/* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
+/*-
+ * ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
* constant time (independent of the concrete value of rec->length, which may
* vary within a 256-byte window).
*
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);
}
}
-/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
+/*-
+ * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
* record.
*
* ctx: the EVP_MD_CTX from which we take the hash function.
* On entry: by virtue of having been through one of the remove_padding
* functions, above, we know that data_plus_mac_size is large enough to contain
* a padding byte and MAC. (If the padding was invalid, it might contain the
- * padding too. ) */
+ * padding too. )
+ */
void ssl3_cbc_digest_record(
const EVP_MD_CTX *ctx,
unsigned char* md_out,
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. */
- b = (b&~is_past_c) | (0x80&is_past_c);
+ b = constant_time_select_8(is_past_c, 0x80, b);
/* If this the the block containing the end of the
* application data and we're past the 0x80 value then
* just write zero. */
if (j >= md_block_size - md_length_size)
{
/* If this is index_b, write a length byte. */
- b = (b&~is_block_b) | (is_block_b&length_bytes[j-(md_block_size-md_length_size)]);
+ b = constant_time_select_8(
+ is_block_b, length_bytes[j-(md_block_size-md_length_size)], b);
}
block[j] = b;
}
projects / openssl.git / blobdiff