*
*/
+#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_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 char a, unsigned char 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.
*
/* SSLv3 requires that the padding is minimal. */
good &= constant_time_ge(block_size, padding_length+1);
rec->length -= good & (padding_length+1);
- 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
* record in |rec| in constant time and returns 1 if the padding is valid and
unsigned mac_size)
{
unsigned padding_length, good, to_check, i;
- const char has_explicit_iv =
- s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION;
- const unsigned overhead = 1 /* padding length byte */ +
- mac_size +
- (has_explicit_iv ? block_size : 0);
-
- /* These lengths are all public so we can test them in non-constant
- * time. */
- if (overhead > rec->length)
+ const unsigned overhead = 1 /* padding length byte */ + mac_size;
+ /* Check if version requires explicit IV */
+ if (SSL_USE_EXPLICIT_IV(s))
+ {
+ /* These lengths are all public so we can test them in
+ * non-constant time.
+ */
+ if (overhead + block_size > rec->length)
+ return 0;
+ /* We can now safely skip explicit IV */
+ rec->data += block_size;
+ rec->input += block_size;
+ rec->length -= block_size;
+ rec->orig_len -= block_size;
+ }
+ else if (overhead > rec->length)
return 0;
padding_length = rec->data[rec->length-1];
}
}
+ if (EVP_CIPHER_flags(s->enc_read_ctx->cipher)&EVP_CIPH_FLAG_AEAD_CIPHER)
+ {
+ /* padding is already verified */
+ rec->length -= padding_length + 1;
+ return 1;
+ }
+
good = constant_time_ge(rec->length, overhead+padding_length);
/* The padding consists of a length byte at the end of the record and
* then that many bytes of padding, all with the same value as the
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);
rec->length -= good & (padding_length+1);
- /* We can always safely skip the explicit IV. We check at the beginning
- * of this function that the record has at least enough space for the
- * IV, MAC and padding length byte. (These can be checked in
- * non-constant time because it's all public information.) So, if the
- * padding was invalid, then we didn't change |rec->length| and this is
- * safe. If the padding was valid then we know that we have at least
- * overhead+padding_length bytes of space and so this is still safe
- * because overhead accounts for the explicit IV. */
- if (has_explicit_iv)
- {
- rec->data += block_size;
- rec->input += block_size;
- rec->length -= block_size;
- rec->orig_len -= block_size;
- }
-
- return (int)((good & 1) | (~good & -1));
+ return constant_time_select_int(good, 1, -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_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);
}
/* 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
}
+/* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
+ * little-endian order. The value of p is advanced by four. */
+#define u32toLE(n, p) \
+ (*((p)++)=(unsigned char)(n), \
+ *((p)++)=(unsigned char)(n>>8), \
+ *((p)++)=(unsigned char)(n>>16), \
+ *((p)++)=(unsigned char)(n>>24))
+
/* These functions serialize the state of a hash and thus perform the standard
* "final" operation without adding the padding and length that such a function
* typically does. */
static void tls1_md5_final_raw(void* ctx, unsigned char *md_out)
{
MD5_CTX *md5 = ctx;
- l2n(md5->A, md_out);
- l2n(md5->B, md_out);
- l2n(md5->C, md_out);
- l2n(md5->D, md_out);
+ u32toLE(md5->A, md_out);
+ u32toLE(md5->B, md_out);
+ u32toLE(md5->C, md_out);
+ u32toLE(md5->D, md_out);
}
static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out)
* 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
/* mdLengthSize is the number of bytes in the length field that terminates
* 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. */
md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform;
md_size = 16;
sslv3_pad_length = 48;
+ length_is_big_endian = 0;
break;
case NID_sha1:
SHA1_Init((SHA_CTX*)md_state.c);
md_transform(md_state.c, hmac_pad);
}
- memset(length_bytes,0,md_length_size-4);
- length_bytes[md_length_size-4] = (unsigned char)(bits>>24);
- length_bytes[md_length_size-3] = (unsigned char)(bits>>16);
- length_bytes[md_length_size-2] = (unsigned char)(bits>>8);
- length_bytes[md_length_size-1] = (unsigned char)bits;
+ if (length_is_big_endian)
+ {
+ memset(length_bytes,0,md_length_size-4);
+ length_bytes[md_length_size-4] = (unsigned char)(bits>>24);
+ length_bytes[md_length_size-3] = (unsigned char)(bits>>16);
+ length_bytes[md_length_size-2] = (unsigned char)(bits>>8);
+ length_bytes[md_length_size-1] = (unsigned char)bits;
+ }
+ else
+ {
+ memset(length_bytes,0,md_length_size);
+ length_bytes[md_length_size-5] = (unsigned char)(bits>>24);
+ length_bytes[md_length_size-6] = (unsigned char)(bits>>16);
+ length_bytes[md_length_size-7] = (unsigned char)(bits>>8);
+ length_bytes[md_length_size-8] = (unsigned char)bits;
+ }
if (k > 0)
{
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;
}
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