/* ====================================================================
* Copyright (c) 2012 The OpenSSL Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. All advertising materials mentioning features or use of this
* software must display the following acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
*
* 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
* endorse or promote products derived from this software without
* prior written permission. For written permission, please contact
* openssl-core@openssl.org.
*
* 5. Products derived from this software may not be called "OpenSSL"
* nor may "OpenSSL" appear in their names without prior written
* permission of the OpenSSL Project.
*
* 6. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit (http://www.openssl.org/)"
*
* THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
* EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
* ====================================================================
*
* This product includes cryptographic software written by Eric Young
* (eay@cryptsoft.com). This product includes software written by Tim
* Hudson (tjh@cryptsoft.com). */
#include <assert.h>
#include <string.h>
#include <openssl/digest.h>
#include <openssl/nid.h>
#include <openssl/sha.h>
#include "../internal.h"
#include "internal.h"
/* TODO(davidben): unsigned should be size_t. The various constant_time
* functions need to be switched to size_t. */
/* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length
* field. (SHA-384/512 have 128-bit length.) */
#define MAX_HASH_BIT_COUNT_BYTES 16
/* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
* Currently SHA-384/512 has a 128-byte block size and that's the largest
* supported by TLS.) */
#define MAX_HASH_BLOCK_SIZE 128
int EVP_tls_cbc_remove_padding(unsigned *out_padding_ok, unsigned *out_len,
const uint8_t *in, unsigned in_len,
unsigned block_size, unsigned mac_size) {
unsigned padding_length, good, to_check, i;
const unsigned overhead = 1 /* padding length byte */ + mac_size;
/* These lengths are all public so we can test them in non-constant time. */
if (overhead > in_len) {
return 0;
}
padding_length = in[in_len - 1];
good = constant_time_ge(in_len, 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
* length byte. Thus, with the length byte included, there are i+1
* bytes of padding.
*
* We can't check just |padding_length+1| bytes because that leaks
* decrypted information. Therefore we always have to check the maximum
* amount of padding possible. (Again, the length of the record is
* public information so we can use it.) */
to_check = 256; /* maximum amount of padding, inc length byte. */
if (to_check > in_len) {
to_check = in_len;
}
for (i = 0; i < to_check; i++) {
uint8_t mask = constant_time_ge_8(padding_length, i);
uint8_t b = in[in_len - 1 - i];
/* The final |padding_length+1| bytes should all have the value
* |padding_length|. Therefore the XOR should be zero. */
good &= ~(mask & (padding_length ^ b));
}
/* 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. */
good = constant_time_eq(0xff, good & 0xff);
/* Always treat |padding_length| as zero on error. If, assuming block size of
* 16, a padding of [<15 arbitrary bytes> 15] treated |padding_length| as 16
* and returned -1, distinguishing good MAC and bad padding from bad MAC and
* bad padding would give POODLE's padding oracle. */
padding_length = good & (padding_length + 1);
*out_len = in_len - padding_length;
*out_padding_ok = good;
return 1;
}
void EVP_tls_cbc_copy_mac(uint8_t *out, unsigned md_size,
const uint8_t *in, unsigned in_len,
unsigned 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. */
unsigned mac_end = in_len;
unsigned 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. */
unsigned 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);
}
unsigned rotate_offset = 0;
uint8_t mac_started = 0;
OPENSSL_memset(rotated_mac, 0, md_size);
for (unsigned i = scan_start, j = 0; i < orig_len; i++, j++) {
if (j >= md_size) {
j -= md_size;
}
unsigned is_mac_start = constant_time_eq(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 (unsigned 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 (unsigned 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);
}
/* u32toBE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
* big-endian order. The value of p is advanced by four. */
#define u32toBE(n, p) \
do { \
*((p)++) = (uint8_t)((n) >> 24); \
*((p)++) = (uint8_t)((n) >> 16); \
*((p)++) = (uint8_t)((n) >> 8); \
*((p)++) = (uint8_t)((n)); \
} while (0)
/* u64toBE serialises an unsigned, 64-bit number (n) as eight bytes at (p) in
* big-endian order. The value of p is advanced by eight. */
#define u64toBE(n, p) \
do { \
*((p)++) = (uint8_t)((n) >> 56); \
*((p)++) = (uint8_t)((n) >> 48); \
*((p)++) = (uint8_t)((n) >> 40); \
*((p)++) = (uint8_t)((n) >> 32); \
*((p)++) = (uint8_t)((n) >> 24); \
*((p)++) = (uint8_t)((n) >> 16); \
*((p)++) = (uint8_t)((n) >> 8); \
*((p)++) = (uint8_t)((n)); \
} while (0)
/* 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_sha1_final_raw(void *ctx, uint8_t *md_out) {
SHA_CTX *sha1 = ctx;
u32toBE(sha1->h[0], md_out);
u32toBE(sha1->h[1], md_out);
u32toBE(sha1->h[2], md_out);
u32toBE(sha1->h[3], md_out);
u32toBE(sha1->h[4], md_out);
}
#define LARGEST_DIGEST_CTX SHA_CTX
static void tls1_sha256_final_raw(void *ctx, uint8_t *md_out) {
SHA256_CTX *sha256 = ctx;
unsigned i;
for (i = 0; i < 8; i++) {
u32toBE(sha256->h[i], md_out);
}
}
#undef LARGEST_DIGEST_CTX
#define LARGEST_DIGEST_CTX SHA256_CTX
static void tls1_sha512_final_raw(void *ctx, uint8_t *md_out) {
SHA512_CTX *sha512 = ctx;
unsigned i;
for (i = 0; i < 8; i++) {
u64toBE(sha512->h[i], md_out);
}
}
#undef LARGEST_DIGEST_CTX
#define LARGEST_DIGEST_CTX SHA512_CTX
int EVP_tls_cbc_record_digest_supported(const EVP_MD *md) {
switch (EVP_MD_type(md)) {
case NID_sha1:
case NID_sha256:
case NID_sha384:
return 1;
default:
return 0;
}
}
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) {
union {
double align;
uint8_t c[sizeof(LARGEST_DIGEST_CTX)];
} md_state;
void (*md_final_raw)(void *ctx, uint8_t *md_out);
void (*md_transform)(void *ctx, const uint8_t *block);
unsigned md_size, md_block_size = 64;
unsigned len, max_mac_bytes, num_blocks, num_starting_blocks, k,
mac_end_offset, c, index_a, index_b;
unsigned int bits; /* at most 18 bits */
uint8_t length_bytes[MAX_HASH_BIT_COUNT_BYTES];
/* hmac_pad is the masked HMAC key. */
uint8_t hmac_pad[MAX_HASH_BLOCK_SIZE];
uint8_t first_block[MAX_HASH_BLOCK_SIZE];
uint8_t mac_out[EVP_MAX_MD_SIZE];
unsigned i, j, md_out_size_u;
EVP_MD_CTX md_ctx;
/* mdLengthSize is the number of bytes in the length field that terminates
* the hash. */
unsigned md_length_size = 8;
/* This is a, hopefully redundant, check that allows us to forget about
* many possible overflows later in this function. */
assert(data_plus_mac_plus_padding_size < 1024 * 1024);
switch (EVP_MD_type(md)) {
case NID_sha1:
SHA1_Init((SHA_CTX *)md_state.c);
md_final_raw = tls1_sha1_final_raw;
md_transform =
(void (*)(void *ctx, const uint8_t *block))SHA1_Transform;
md_size = 20;
break;
case NID_sha256:
SHA256_Init((SHA256_CTX *)md_state.c);
md_final_raw = tls1_sha256_final_raw;
md_transform =
(void (*)(void *ctx, const uint8_t *block))SHA256_Transform;
md_size = 32;
break;
case NID_sha384:
SHA384_Init((SHA512_CTX *)md_state.c);
md_final_raw = tls1_sha512_final_raw;
md_transform =
(void (*)(void *ctx, const uint8_t *block))SHA512_Transform;
md_size = 384 / 8;
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 unsigned 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 unsigned kVarianceBlocks = 6;
/* From now on we're dealing with the MAC, which conceptually has 13
* bytes of `header' before the start of the data. */
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. */
max_mac_bytes = len - md_size - 1;
/* num_blocks is the maximum number of hash blocks. */
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. */
num_starting_blocks = 0;
/* k is the starting byte offset into the conceptual header||data where
* we start processing. */
k = 0;
/* mac_end_offset is the index just past the end of the data to be
* MACed. */
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. */
c = mac_end_offset % md_block_size;
/* index_a is the hash block number that contains the 0x80 terminating
* value. */
index_a = mac_end_offset / md_block_size;
/* index_b is the hash block number that contains the 64-bit hash
* length, in bits. */
index_b = (mac_end_offset + md_length_size) / md_block_size;
/* bits is the hash-length in bits. It includes the additional hash
* block for the masked HMAC key. */
if (num_blocks > kVarianceBlocks) {
num_starting_blocks = num_blocks - kVarianceBlocks;
k = md_block_size * num_starting_blocks;
}
bits = 8 * mac_end_offset;
/* Compute the initial HMAC block. */
bits += 8 * md_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 (i = 0; i < md_block_size; i++) {
hmac_pad[i] ^= 0x36;
}
md_transform(md_state.c, hmac_pad);
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. */
OPENSSL_memcpy(first_block, header, 13);
OPENSSL_memcpy(first_block + 13, data, md_block_size - 13);
md_transform(md_state.c, first_block);
for (i = 1; i < k / md_block_size; i++) {
md_transform(md_state.c, data + md_block_size * i - 13);
}
}
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 (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 (j = 0; j < md_block_size; j++) {
uint8_t b = 0, is_past_c, is_past_cp1;
if (k < kHeaderLength) {
b = header[k];
} else if (k < data_plus_mac_plus_padding_size + kHeaderLength) {
b = data[k - kHeaderLength];
}
k++;
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 = 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.c, block);
md_final_raw(md_state.c, block);
/* If this is index_b, copy the hash value to |mac_out|. */
for (j = 0; j < md_size; j++) {
mac_out[j] |= block[j] & is_block_b;
}
}
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 (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);
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;
}