#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)
{
}
/* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
-static unsigned char constant_time_eq_8(unsigned char a, unsigned char b)
+static unsigned char constant_time_eq_8(unsigned a, unsigned b)
{
unsigned c = a ^ b;
c--;
unsigned padding_length, good, to_check, i;
const unsigned overhead = 1 /* padding length byte */ + mac_size;
/* Check if version requires explicit IV */
- if (s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION)
+ if (SSL_USE_EXPLICIT_IV(s))
{
/* These lengths are all public so we can test them in
* non-constant time.
return (int)((good & 1) | (~good & -1));
}
-#if defined(_M_AMD64) || defined(__x86_64__)
-#define CBC_MAC_ROTATE_IN_PLACE
-#endif
-
/* 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).
*
* If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
* variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
- * a single cache-line, then the variable memory accesses don't actually affect
- * the timing. This has been tested to be true on Intel amd64 chips.
+ * a single or pair of cache-lines, then the variable memory accesses don't
+ * actually affect the timing. CPUs with smaller cache-lines [if any] are
+ * not multi-core and are not considered vulnerable to cache-timing attacks.
*/
+#define CBC_MAC_ROTATE_IN_PLACE
+
void ssl3_cbc_copy_mac(unsigned char* out,
const SSL3_RECORD *rec,
unsigned md_size)
{
#if defined(CBC_MAC_ROTATE_IN_PLACE)
- unsigned char rotated_mac_buf[EVP_MAX_MD_SIZE*2];
+ unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE];
unsigned char *rotated_mac;
#else
unsigned char rotated_mac[EVP_MAX_MD_SIZE];
OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
#if defined(CBC_MAC_ROTATE_IN_PLACE)
- rotated_mac = (unsigned char*) (((intptr_t)(rotated_mac_buf + 64)) & ~63);
+ rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63);
#endif
/* This information is public so it's safe to branch based on it. */
rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
memset(rotated_mac, 0, md_size);
- for (i = scan_start; i < rec->orig_len;)
+ for (i = scan_start, j = 0; i < rec->orig_len; i++)
{
- for (j = 0; j < md_size && i < rec->orig_len; i++, j++)
- {
- unsigned char mac_started = constant_time_ge(i, mac_start);
- unsigned char mac_ended = constant_time_ge(i, mac_end);
- unsigned char b = 0;
- b = rec->data[i];
- rotated_mac[j] |= b & mac_started & ~mac_ended;
- }
+ unsigned char mac_started = constant_time_ge(i, mac_start);
+ unsigned char mac_ended = constant_time_ge(i, mac_end);
+ unsigned char b = rec->data[i];
+ rotated_mac[j++] |= b & mac_started & ~mac_ended;
+ j &= constant_time_lt(j,md_size);
}
/* Now rotate the MAC */
j = 0;
for (i = 0; i < md_size; i++)
{
- unsigned char offset = (div_spoiler + rotate_offset + i) % md_size;
- out[j++] = rotated_mac[offset];
+ /* in case cache-line is 32 bytes, touch second line */
+ ((volatile unsigned char *)rotated_mac)[rotate_offset^32];
+ out[j++] = rotated_mac[rotate_offset++];
+ rotate_offset &= constant_time_lt(rotate_offset,md_size);
}
#else
memset(out, 0, md_size);
+ rotate_offset = md_size - rotate_offset;
+ rotate_offset &= constant_time_lt(rotate_offset,md_size);
for (i = 0; i < md_size; i++)
{
- unsigned char offset = (div_spoiler + md_size - rotate_offset + i) % md_size;
for (j = 0; j < md_size; j++)
- out[j] |= rotated_mac[i] & constant_time_eq_8(j, offset);
+ out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);
+ rotate_offset++;
+ rotate_offset &= constant_time_lt(rotate_offset,md_size);
}
#endif
}
* md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
* md_out_size: if non-NULL, the number of output bytes is written here.
* header: the 13-byte, TLS record header.
- * data: the record data itself, less any preceeding explicit IV.
+ * data: the record data itself, less any preceding explicit IV.
* data_plus_mac_size: the secret, reported length of the data and MAC
* once the padding has been removed.
* data_plus_mac_plus_padding_size: the public length of the whole
* the hash. */
unsigned md_length_size = 8;
char length_is_big_endian = 1;
+ int ret;
/* This is a, hopefully redundant, check that allows us to forget about
* many possible overflows later in this function. */
EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
EVP_DigestUpdate(&md_ctx, mac_out, md_size);
}
- EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
- if (md_out_size)
+ ret = EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
+ if (ret && md_out_size)
*md_out_size = md_out_size_u;
EVP_MD_CTX_cleanup(&md_ctx);
}
projects / openssl.git / blobdiff