| /* ==================================================================== |
| * 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; |
| /* 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; |
| unsigned i, j; |
| unsigned rotate_offset; |
| |
| assert(orig_len >= in_len); |
| assert(in_len >= md_size); |
| assert(md_size <= EVP_MAX_MD_SIZE); |
| |
| /* 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); |
| } |
| |
| /* Ideally the next statement would be: |
| * |
| * rotate_offset = (mac_start - scan_start) % md_size; |
| * |
| * However, division is not a constant-time operation (at least on Intel |
| * chips). Thus we enumerate the possible values of md_size and handle each |
| * separately. The value of |md_size| is public information (it's determined |
| * by the cipher suite in the ServerHello) so our timing can vary based on |
| * its value. */ |
| |
| rotate_offset = mac_start - scan_start; |
| /* rotate_offset can be, at most, 255 (bytes of padding) + 1 (padding length) |
| * + md_size = 256 + 48 (since SHA-384 is the largest hash) = 304. */ |
| assert(rotate_offset <= 304); |
| |
| /* Below is an SMT-LIB2 verification that the Barrett reductions below are |
| * correct within this range: |
| * |
| * (define-fun barrett ( |
| * (x (_ BitVec 32)) |
| * (mul (_ BitVec 32)) |
| * (shift (_ BitVec 32)) |
| * (divisor (_ BitVec 32)) ) (_ BitVec 32) |
| * (let ((q (bvsub x (bvmul divisor (bvlshr (bvmul x mul) shift))) )) |
| * (ite (bvuge q divisor) |
| * (bvsub q divisor) |
| * q))) |
| * |
| * (declare-fun x () (_ BitVec 32)) |
| * |
| * (assert (or |
| * (let ( |
| * (divisor (_ bv20 32)) |
| * (mul (_ bv25 32)) |
| * (shift (_ bv9 32)) |
| * (limit (_ bv853 32))) |
| * |
| * (and (bvule x limit) (not (= (bvurem x divisor) |
| * (barrett x mul shift divisor))))) |
| * |
| * (let ( |
| * (divisor (_ bv48 32)) |
| * (mul (_ bv10 32)) |
| * (shift (_ bv9 32)) |
| * (limit (_ bv768 32))) |
| * |
| * (and (bvule x limit) (not (= (bvurem x divisor) |
| * (barrett x mul shift divisor))))) |
| * )) |
| * |
| * (check-sat) |
| * (get-model) |
| */ |
| |
| if (md_size == 16) { |
| rotate_offset &= 15; |
| } else if (md_size == 20) { |
| /* 1/20 is approximated as 25/512 and then Barrett reduction is used. |
| * Analytically, this is correct for 0 <= rotate_offset <= 853. */ |
| unsigned q = (rotate_offset * 25) >> 9; |
| rotate_offset -= q * 20; |
| rotate_offset -= |
| constant_time_select(constant_time_ge(rotate_offset, 20), 20, 0); |
| } else if (md_size == 32) { |
| rotate_offset &= 31; |
| } else if (md_size == 48) { |
| /* 1/48 is approximated as 10/512 and then Barrett reduction is used. |
| * Analytically, this is correct for 0 <= rotate_offset <= 768. */ |
| unsigned q = (rotate_offset * 10) >> 9; |
| rotate_offset -= q * 48; |
| rotate_offset -= |
| constant_time_select(constant_time_ge(rotate_offset, 48), 48, 0); |
| } else { |
| /* This should be impossible therefore this path doesn't run in constant |
| * time. */ |
| assert(0); |
| rotate_offset = rotate_offset % md_size; |
| } |
| |
| memset(rotated_mac, 0, md_size); |
| for (i = scan_start, j = 0; i < orig_len; i++) { |
| uint8_t mac_started = constant_time_ge_8(i, mac_start); |
| uint8_t mac_ended = constant_time_ge_8(i, mac_end); |
| uint8_t b = in[i]; |
| rotated_mac[j++] |= b & mac_started & ~mac_ended; |
| j &= constant_time_lt(j, md_size); |
| } |
| |
| /* 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 (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; |
| } |
| |
| 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) \ |
| (*((p)++)=(uint8_t)(n>>24), \ |
| *((p)++)=(uint8_t)(n>>16), \ |
| *((p)++)=(uint8_t)(n>>8), \ |
| *((p)++)=(uint8_t)(n)) |
| |
| /* 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) \ |
| (*((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)) |
| |
| /* 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; |
| memset(hmac_pad, 0, md_block_size); |
| assert(mac_secret_length <= sizeof(hmac_pad)); |
| 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); |
| |
| 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. */ |
| memcpy(first_block, header, 13); |
| 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); |
| } |
| } |
| |
| 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; |
| } |