static int test_select_8(unsigned char a, unsigned char b)
{
unsigned char selected = constant_time_select_8(CONSTTIME_TRUE_8, a, b);
if (selected != a) {
fprintf(stderr, "Test failed for constant_time_select(%u, %u,"
"%u): expected %u(first value), got %u\n",
CONSTTIME_TRUE, a, b, a, selected);
return 1;
}
selected = constant_time_select_8(CONSTTIME_FALSE_8, a, b);
if (selected != b) {
fprintf(stderr, "Test failed for constant_time_select(%u, %u,"
"%u): expected %u(second value), got %u\n",
CONSTTIME_FALSE, a, b, b, selected);
return 1;
}
return 0;
}
void EVP_tls_cbc_copy_mac(uint8_t *out, size_t md_size, const uint8_t *in,
size_t in_len, size_t orig_len) {
uint8_t rotated_mac1[EVP_MAX_MD_SIZE], rotated_mac2[EVP_MAX_MD_SIZE];
uint8_t *rotated_mac = rotated_mac1;
uint8_t *rotated_mac_tmp = rotated_mac2;
/* mac_end is the index of |in| just after the end of the MAC. */
size_t mac_end = in_len;
size_t mac_start = mac_end - md_size;
assert(orig_len >= in_len);
assert(in_len >= md_size);
assert(md_size <= EVP_MAX_MD_SIZE);
/* scan_start contains the number of bytes that we can ignore because
* the MAC's position can only vary by 255 bytes. */
size_t scan_start = 0;
/* This information is public so it's safe to branch based on it. */
if (orig_len > md_size + 255 + 1) {
scan_start = orig_len - (md_size + 255 + 1);
}
size_t rotate_offset = 0;
uint8_t mac_started = 0;
OPENSSL_memset(rotated_mac, 0, md_size);
for (size_t i = scan_start, j = 0; i < orig_len; i++, j++) {
if (j >= md_size) {
j -= md_size;
}
crypto_word_t is_mac_start = constant_time_eq_w(i, mac_start);
mac_started |= is_mac_start;
uint8_t mac_ended = constant_time_ge_8(i, mac_end);
rotated_mac[j] |= in[i] & mac_started & ~mac_ended;
/* Save the offset that |mac_start| is mapped to. */
rotate_offset |= j & is_mac_start;
}
/* Now rotate the MAC. We rotate in log(md_size) steps, one for each bit
* position. */
for (size_t offset = 1; offset < md_size; offset <<= 1, rotate_offset >>= 1) {
/* Rotate by |offset| iff the corresponding bit is set in
* |rotate_offset|, placing the result in |rotated_mac_tmp|. */
const uint8_t skip_rotate = (rotate_offset & 1) - 1;
for (size_t i = 0, j = offset; i < md_size; i++, j++) {
if (j >= md_size) {
j -= md_size;
}
rotated_mac_tmp[i] =
constant_time_select_8(skip_rotate, rotated_mac[i], rotated_mac[j]);
}
/* Swap pointers so |rotated_mac| contains the (possibly) rotated value.
* Note the number of iterations and thus the identity of these pointers is
* public information. */
uint8_t *tmp = rotated_mac;
rotated_mac = rotated_mac_tmp;
rotated_mac_tmp = tmp;
}
OPENSSL_memcpy(out, rotated_mac, md_size);
}
int EVP_tls_cbc_digest_record(const EVP_MD *md, uint8_t *md_out,
size_t *md_out_size, const uint8_t header[13],
const uint8_t *data, size_t data_plus_mac_size,
size_t data_plus_mac_plus_padding_size,
const uint8_t *mac_secret,
unsigned mac_secret_length) {
HASH_CTX md_state;
void (*md_final_raw)(HASH_CTX *ctx, uint8_t *md_out);
void (*md_transform)(HASH_CTX *ctx, const uint8_t *block);
unsigned md_size, md_block_size = 64;
/* md_length_size is the number of bytes in the length field that terminates
* the hash. */
unsigned md_length_size = 8;
/* Bound the acceptable input so we can forget about many possible overflows
* later in this function. This is redundant with the record size limits in
* TLS. */
if (data_plus_mac_plus_padding_size >= 1024 * 1024) {
assert(0);
return 0;
}
switch (EVP_MD_type(md)) {
case NID_sha1:
SHA1_Init(&md_state.sha1);
md_final_raw = tls1_sha1_final_raw;
md_transform = tls1_sha1_transform;
md_size = SHA_DIGEST_LENGTH;
break;
case NID_sha256:
SHA256_Init(&md_state.sha256);
md_final_raw = tls1_sha256_final_raw;
md_transform = tls1_sha256_transform;
md_size = SHA256_DIGEST_LENGTH;
break;
case NID_sha384:
SHA384_Init(&md_state.sha512);
md_final_raw = tls1_sha512_final_raw;
md_transform = tls1_sha512_transform;
md_size = SHA384_DIGEST_LENGTH;
md_block_size = 128;
md_length_size = 16;
break;
default:
/* EVP_tls_cbc_record_digest_supported should have been called first to
* check that the hash function is supported. */
assert(0);
*md_out_size = 0;
return 0;
}
assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
assert(md_size <= EVP_MAX_MD_SIZE);
static const size_t kHeaderLength = 13;
/* kVarianceBlocks is the number of blocks of the hash that we have to
* calculate in constant time because they could be altered by the
* padding value.
*
* TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
* required to be minimal. Therefore we say that the final six blocks
* can vary based on the padding. */
static const size_t kVarianceBlocks = 6;
/* From now on we're dealing with the MAC, which conceptually has 13
* bytes of `header' before the start of the data. */
size_t len = data_plus_mac_plus_padding_size + kHeaderLength;
/* max_mac_bytes contains the maximum bytes of bytes in the MAC, including
* |header|, assuming that there's no padding. */
size_t max_mac_bytes = len - md_size - 1;
/* num_blocks is the maximum number of hash blocks. */
size_t num_blocks =
(max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size;
/* In order to calculate the MAC in constant time we have to handle
* the final blocks specially because the padding value could cause the
* end to appear somewhere in the final |kVarianceBlocks| blocks and we
* can't leak where. However, |num_starting_blocks| worth of data can
* be hashed right away because no padding value can affect whether
* they are plaintext. */
size_t num_starting_blocks = 0;
/* k is the starting byte offset into the conceptual header||data where
* we start processing. */
size_t k = 0;
/* mac_end_offset is the index just past the end of the data to be
* MACed. */
size_t mac_end_offset = data_plus_mac_size + kHeaderLength - md_size;
/* c is the index of the 0x80 byte in the final hash block that
* contains application data. */
size_t c = mac_end_offset % md_block_size;
/* index_a is the hash block number that contains the 0x80 terminating
* value. */
size_t index_a = mac_end_offset / md_block_size;
/* index_b is the hash block number that contains the 64-bit hash
* length, in bits. */
size_t index_b = (mac_end_offset + md_length_size) / md_block_size;
if (num_blocks > kVarianceBlocks) {
num_starting_blocks = num_blocks - kVarianceBlocks;
k = md_block_size * num_starting_blocks;
}
/* bits is the hash-length in bits. It includes the additional hash
* block for the masked HMAC key. */
size_t bits = 8 * mac_end_offset; /* at most 18 bits to represent */
/* Compute the initial HMAC block. */
bits += 8 * md_block_size;
/* hmac_pad is the masked HMAC key. */
uint8_t hmac_pad[MAX_HASH_BLOCK_SIZE];
OPENSSL_memset(hmac_pad, 0, md_block_size);
assert(mac_secret_length <= sizeof(hmac_pad));
OPENSSL_memcpy(hmac_pad, mac_secret, mac_secret_length);
for (size_t i = 0; i < md_block_size; i++) {
hmac_pad[i] ^= 0x36;
}
md_transform(&md_state, hmac_pad);
/* The length check means |bits| fits in four bytes. */
uint8_t length_bytes[MAX_HASH_BIT_COUNT_BYTES];
OPENSSL_memset(length_bytes, 0, md_length_size - 4);
length_bytes[md_length_size - 4] = (uint8_t)(bits >> 24);
length_bytes[md_length_size - 3] = (uint8_t)(bits >> 16);
length_bytes[md_length_size - 2] = (uint8_t)(bits >> 8);
length_bytes[md_length_size - 1] = (uint8_t)bits;
if (k > 0) {
/* k is a multiple of md_block_size. */
uint8_t first_block[MAX_HASH_BLOCK_SIZE];
OPENSSL_memcpy(first_block, header, 13);
OPENSSL_memcpy(first_block + 13, data, md_block_size - 13);
md_transform(&md_state, first_block);
for (size_t i = 1; i < k / md_block_size; i++) {
md_transform(&md_state, data + md_block_size * i - 13);
}
}
uint8_t mac_out[EVP_MAX_MD_SIZE];
OPENSSL_memset(mac_out, 0, sizeof(mac_out));
/* We now process the final hash blocks. For each block, we construct
* it in constant time. If the |i==index_a| then we'll include the 0x80
* bytes and zero pad etc. For each block we selectively copy it, in
* constant time, to |mac_out|. */
for (size_t i = num_starting_blocks;
i <= num_starting_blocks + kVarianceBlocks; i++) {
uint8_t block[MAX_HASH_BLOCK_SIZE];
uint8_t is_block_a = constant_time_eq_8(i, index_a);
uint8_t is_block_b = constant_time_eq_8(i, index_b);
for (size_t j = 0; j < md_block_size; j++) {
uint8_t b = 0;
if (k < kHeaderLength) {
b = header[k];
} else if (k < data_plus_mac_plus_padding_size + kHeaderLength) {
b = data[k - kHeaderLength];
}
k++;
uint8_t is_past_c = is_block_a & constant_time_ge_8(j, c);
uint8_t 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 = 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. */
b = b & ~is_past_cp1;
/* If this is index_b (the final block), but not
* index_a (the end of the data), then the 64-bit
* length didn't fit into index_a and we're having to
* add an extra block of zeros. */
b &= ~is_block_b | is_block_a;
/* The final bytes of one of the blocks contains the
* length. */
if (j >= md_block_size - md_length_size) {
/* If this is index_b, write a length byte. */
b = constant_time_select_8(
is_block_b, length_bytes[j - (md_block_size - md_length_size)], b);
}
block[j] = b;
}
md_transform(&md_state, block);
md_final_raw(&md_state, block);
/* If this is index_b, copy the hash value to |mac_out|. */
for (size_t j = 0; j < md_size; j++) {
mac_out[j] |= block[j] & is_block_b;
}
}
EVP_MD_CTX md_ctx;
EVP_MD_CTX_init(&md_ctx);
if (!EVP_DigestInit_ex(&md_ctx, md, NULL /* engine */)) {
EVP_MD_CTX_cleanup(&md_ctx);
return 0;
}
/* Complete the HMAC in the standard manner. */
for (size_t i = 0; i < md_block_size; i++) {
hmac_pad[i] ^= 0x6a;
}
EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
EVP_DigestUpdate(&md_ctx, mac_out, md_size);
unsigned md_out_size_u;
EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
*md_out_size = md_out_size_u;
EVP_MD_CTX_cleanup(&md_ctx);
return 1;
}
int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
const unsigned char *from, int flen,
int num)
{
int i;
/* |em| is the encoded message, zero-padded to exactly |num| bytes */
unsigned char *em = NULL;
unsigned int good, found_zero_byte, mask;
int zero_index = 0, msg_index, mlen = -1;
if (tlen < 0 || flen < 0)
return -1;
/*
* PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
* section 7.2.2.
*/
if (flen > num || num < 11) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
RSA_R_PKCS_DECODING_ERROR);
return -1;
}
em = OPENSSL_malloc(num);
if (em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
return -1;
}
/*
* Caller is encouraged to pass zero-padded message created with
* BN_bn2binpad. Trouble is that since we can't read out of |from|'s
* bounds, it's impossible to have an invariant memory access pattern
* in case |from| was not zero-padded in advance.
*/
for (from += flen, em += num, i = 0; i < num; i++) {
mask = ~constant_time_is_zero(flen);
flen -= 1 & mask;
from -= 1 & mask;
*--em = *from & mask;
}
from = em;
good = constant_time_is_zero(from[0]);
good &= constant_time_eq(from[1], 2);
/* scan over padding data */
found_zero_byte = 0;
for (i = 2; i < num; i++) {
unsigned int equals0 = constant_time_is_zero(from[i]);
zero_index = constant_time_select_int(~found_zero_byte & equals0,
i, zero_index);
found_zero_byte |= equals0;
}
/*
* PS must be at least 8 bytes long, and it starts two bytes into |from|.
* If we never found a 0-byte, then |zero_index| is 0 and the check
* also fails.
*/
good &= constant_time_ge(zero_index, 2 + 8);
/*
* Skip the zero byte. This is incorrect if we never found a zero-byte
* but in this case we also do not copy the message out.
*/
msg_index = zero_index + 1;
mlen = num - msg_index;
/*
* For good measure, do this check in constant time as well.
*/
good &= constant_time_ge(tlen, mlen);
/*
* Even though we can't fake result's length, we can pretend copying
* |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
* bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
* where |mlen'| is "saturated" |mlen| value. Deducing information
* about failure or |mlen| would take attacker's ability to observe
* memory access pattern with byte granularity *as it occurs*. It
* should be noted that failure is indistinguishable from normal
* operation if |tlen| is fixed by protocol.
*/
tlen = constant_time_select_int(constant_time_lt(num, tlen), num, tlen);
msg_index = constant_time_select_int(good, msg_index, num - tlen);
mlen = num - msg_index;
for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
unsigned int equals = constant_time_eq(i, mlen);
from -= tlen & equals; /* if (i == mlen) rewind */
mask &= mask ^ equals; /* if (i == mlen) mask = 0 */
to[i] = constant_time_select_8(mask, from[i], to[i]);
}
OPENSSL_cleanse(em, num);
OPENSSL_free(em);
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
err_clear_last_constant_time(1 & good);
return constant_time_select_int(good, mlen, -1);
}
