/* ==================================================================== * 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 #include #include #include #include #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_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 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); } /* 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); 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 */ #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->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; }