/* ==================================================================== * 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" #include "../fipsmodule/cipher/internal.h" // 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(crypto_word_t *out_padding_ok, size_t *out_len, const uint8_t *in, size_t in_len, size_t block_size, size_t mac_size) { const size_t 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; } size_t padding_length = in[in_len - 1]; crypto_word_t good = constant_time_ge_w(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.) size_t to_check = 256; // maximum amount of padding, inc length byte. if (to_check > in_len) { to_check = in_len; } for (size_t 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_w(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, 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); } // 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) typedef union { SHA_CTX sha1; SHA256_CTX sha256; SHA512_CTX sha512; } HASH_CTX; static void tls1_sha1_transform(HASH_CTX *ctx, const uint8_t *block) { SHA1_Transform(&ctx->sha1, block); } static void tls1_sha256_transform(HASH_CTX *ctx, const uint8_t *block) { SHA256_Transform(&ctx->sha256, block); } static void tls1_sha512_transform(HASH_CTX *ctx, const uint8_t *block) { SHA512_Transform(&ctx->sha512, block); } // 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(HASH_CTX *ctx, uint8_t *md_out) { SHA_CTX *sha1 = &ctx->sha1; 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); } static void tls1_sha256_final_raw(HASH_CTX *ctx, uint8_t *md_out) { SHA256_CTX *sha256 = &ctx->sha256; for (unsigned i = 0; i < 8; i++) { u32toBE(sha256->h[i], md_out); } } static void tls1_sha512_final_raw(HASH_CTX *ctx, uint8_t *md_out) { SHA512_CTX *sha512 = &ctx->sha512; for (unsigned i = 0; i < 8; i++) { u64toBE(sha512->h[i], md_out); } } 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) { 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_block_shift = 6; // 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_block_shift = 7; 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_block_size == (1u << md_block_shift)); 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 |kVarianceBlocks| // blocks can vary based on the padding and on the hash used. This value // must be derived from public information. const size_t kVarianceBlocks = ( 255 + 1 + // maximum padding bytes + padding length md_size + // length of hash's output md_block_size - 1 // ceiling ) / md_block_size + 1; // the 0x80 marker and the encoded message length could or not // require an extra block; since the exact value depends on the // message length; thus, one extra block is always added to run // in constant time. // 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 - 1); // index_a is the hash block number that contains the 0x80 terminating value. size_t index_a = mac_end_offset >> md_block_shift; // 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_shift; 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; }