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Diffstat (limited to 'src/crypto/cipher/tls_cbc.c')
| -rw-r--r-- | src/crypto/cipher/tls_cbc.c | 495 |
1 files changed, 495 insertions, 0 deletions
diff --git a/src/crypto/cipher/tls_cbc.c b/src/crypto/cipher/tls_cbc.c new file mode 100644 index 0000000..8bca2f3 --- /dev/null +++ b/src/crypto/cipher/tls_cbc.c @@ -0,0 +1,495 @@ +/* ==================================================================== + * 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/obj.h> +#include <openssl/sha.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_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; + + return constant_time_select_int(good, 1, -1); +} + +/* If CBC_MAC_ROTATE_IN_PLACE is defined then EVP_tls_cbc_copy_mac is performed + * with variable accesses in a 64-byte-aligned buffer. Assuming that this fits + * into 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 EVP_tls_cbc_copy_mac(uint8_t *out, unsigned md_size, + const uint8_t *in, unsigned in_len, + unsigned orig_len) { +#if defined(CBC_MAC_ROTATE_IN_PLACE) + uint8_t rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; + uint8_t *rotated_mac; +#else + uint8_t rotated_mac[EVP_MAX_MD_SIZE]; +#endif + + /* 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 div_spoiler; + unsigned rotate_offset; + + assert(orig_len >= in_len); + assert(in_len >= md_size); + assert(md_size <= EVP_MAX_MD_SIZE); + +#if defined(CBC_MAC_ROTATE_IN_PLACE) + 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. */ + if (orig_len > md_size + 255 + 1) { + scan_start = orig_len - (md_size + 255 + 1); + } + /* div_spoiler contains a multiple of md_size that is used to cause the + * modulo operation to be constant time. Without this, the time varies + * based on the amount of padding when running on Intel chips at least. + * + * The aim of right-shifting md_size is so that the compiler doesn't + * figure out that it can remove div_spoiler as that would require it + * to prove that md_size is always even, which I hope is beyond it. */ + div_spoiler = md_size >> 1; + div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; + rotate_offset = (div_spoiler + mac_start - scan_start) % 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 */ +#if defined(CBC_MAC_ROTATE_IN_PLACE) + j = 0; + for (i = 0; i < md_size; i++) { + /* in case cache-line is 32 bytes, touch second line */ + ((volatile uint8_t *)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++) { + for (j = 0; j < md_size; j++) { + out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); + } + rotate_offset++; + rotate_offset &= constant_time_lt(rotate_offset, md_size); + } +#endif +} + +/* 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->h0, md_out); + u32toBE(sha1->h1, md_out); + u32toBE(sha1->h2, md_out); + u32toBE(sha1->h3, md_out); + u32toBE(sha1->h4, 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; +} |