/* * Copyright 2012-2018 The OpenSSL Project Authors. All Rights Reserved. * * Licensed under the OpenSSL license (the "License"). You may not use * this file except in compliance with the License. You can obtain a copy * in the file LICENSE in the source distribution or at * https://www.openssl.org/source/license.html */ #include "internal/constant_time.h" #include "ssl_local.h" #include "internal/cryptlib.h" #include #include /* * 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 /* * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in * little-endian order. The value of p is advanced by four. */ #define u32toLE(n, p) \ (*((p)++)=(unsigned char)(n), \ *((p)++)=(unsigned char)(n>>8), \ *((p)++)=(unsigned char)(n>>16), \ *((p)++)=(unsigned char)(n>>24)) /* * 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_md5_final_raw(void *ctx, unsigned char *md_out) { MD5_CTX *md5 = ctx; u32toLE(md5->A, md_out); u32toLE(md5->B, md_out); u32toLE(md5->C, md_out); u32toLE(md5->D, md_out); } static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out) { SHA_CTX *sha1 = ctx; l2n(sha1->h0, md_out); l2n(sha1->h1, md_out); l2n(sha1->h2, md_out); l2n(sha1->h3, md_out); l2n(sha1->h4, md_out); } static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out) { SHA256_CTX *sha256 = ctx; unsigned i; for (i = 0; i < 8; i++) { l2n(sha256->h[i], md_out); } } static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out) { SHA512_CTX *sha512 = ctx; unsigned i; for (i = 0; i < 8; i++) { l2n8(sha512->h[i], md_out); } } #undef LARGEST_DIGEST_CTX #define LARGEST_DIGEST_CTX SHA512_CTX /* * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function * which ssl3_cbc_digest_record supports. */ char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) { switch (EVP_MD_CTX_type(ctx)) { case NID_md5: case NID_sha1: case NID_sha224: case NID_sha256: case NID_sha384: case NID_sha512: return 1; default: return 0; } } /*- * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS * record. * * ctx: the EVP_MD_CTX from which we take the hash function. * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. * md_out_size: if non-NULL, the number of output bytes is written here. * header: the 13-byte, TLS record header. * data: the record data itself, less any preceding explicit IV. * data_plus_mac_size: the secret, reported length of the data and MAC * once the padding has been removed. * data_plus_mac_plus_padding_size: the public length of the whole * record, including padding. * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. * * On entry: by virtue of having been through one of the remove_padding * functions, above, we know that data_plus_mac_size is large enough to contain * a padding byte and MAC. (If the padding was invalid, it might contain the * padding too. ) * Returns 1 on success or 0 on error */ int ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, unsigned char *md_out, size_t *md_out_size, const unsigned char header[13], const unsigned char *data, size_t data_plus_mac_size, size_t data_plus_mac_plus_padding_size, const unsigned char *mac_secret, size_t mac_secret_length, char is_sslv3) { union { double align; unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state; void (*md_final_raw) (void *ctx, unsigned char *md_out); void (*md_transform) (void *ctx, const unsigned char *block); size_t md_size, md_block_size = 64; size_t sslv3_pad_length = 40, header_length, variance_blocks, len, max_mac_bytes, num_blocks, num_starting_blocks, k, mac_end_offset, c, index_a, index_b; size_t bits; /* at most 18 bits */ unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; /* hmac_pad is the masked HMAC key. */ unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; unsigned char first_block[MAX_HASH_BLOCK_SIZE]; unsigned char mac_out[EVP_MAX_MD_SIZE]; size_t i, j; unsigned md_out_size_u; EVP_MD_CTX *md_ctx = NULL; /* * mdLengthSize is the number of bytes in the length field that * terminates * the hash. */ size_t md_length_size = 8; char length_is_big_endian = 1; int ret; /* * This is a, hopefully redundant, check that allows us to forget about * many possible overflows later in this function. */ if (!ossl_assert(data_plus_mac_plus_padding_size < 1024 * 1024)) return 0; switch (EVP_MD_CTX_type(ctx)) { case NID_md5: if (MD5_Init((MD5_CTX *)md_state.c) <= 0) return 0; md_final_raw = tls1_md5_final_raw; md_transform = (void (*)(void *ctx, const unsigned char *block))MD5_Transform; md_size = 16; sslv3_pad_length = 48; length_is_big_endian = 0; break; case NID_sha1: if (SHA1_Init((SHA_CTX *)md_state.c) <= 0) return 0; md_final_raw = tls1_sha1_final_raw; md_transform = (void (*)(void *ctx, const unsigned char *block))SHA1_Transform; md_size = 20; break; case NID_sha224: if (SHA224_Init((SHA256_CTX *)md_state.c) <= 0) return 0; md_final_raw = tls1_sha256_final_raw; md_transform = (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; md_size = 224 / 8; break; case NID_sha256: if (SHA256_Init((SHA256_CTX *)md_state.c) <= 0) return 0; md_final_raw = tls1_sha256_final_raw; md_transform = (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; md_size = 32; break; case NID_sha384: if (SHA384_Init((SHA512_CTX *)md_state.c) <= 0) return 0; md_final_raw = tls1_sha512_final_raw; md_transform = (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; md_size = 384 / 8; md_block_size = 128; md_length_size = 16; break; case NID_sha512: if (SHA512_Init((SHA512_CTX *)md_state.c) <= 0) return 0; md_final_raw = tls1_sha512_final_raw; md_transform = (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; md_size = 64; md_block_size = 128; md_length_size = 16; break; default: /* * ssl3_cbc_record_digest_supported should have been called first to * check that the hash function is supported. */ if (md_out_size != NULL) *md_out_size = 0; return ossl_assert(0); } if (!ossl_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES) || !ossl_assert(md_block_size <= MAX_HASH_BLOCK_SIZE) || !ossl_assert(md_size <= EVP_MAX_MD_SIZE)) return 0; header_length = 13; if (is_sslv3) { header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence * number */ + 1 /* record type */ + 2 /* record length */ ; } /* * variance_blocks 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. In SSLv3, the padding must be minimal so the end of * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes * of hash termination (0x80 + 64-bit length) don't fit in the final * block, we say that the final two blocks can vary based on the padding. * 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 |variance_blocks| * blocks can * vary based on the padding. Later in the function, if the message is * short and there obviously cannot be this many blocks then * variance_blocks can be reduced. */ variance_blocks = is_sslv3 ? 2 : ( ((255 + 1 + md_size + md_block_size - 1) / md_block_size) + 1); /* * From now on we're dealing with the MAC, which conceptually has 13 * bytes of `header' before the start of the data (TLS) or 71/75 bytes * (SSLv3) */ len = data_plus_mac_plus_padding_size + header_length; /* * 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 |variance_blocks| 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 + header_length - 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, or whole of |header| in the case of SSLv3. */ /* * For SSLv3, if we're going to have any starting blocks then we need at * least two because the header is larger than a single block. */ if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) { num_starting_blocks = num_blocks - variance_blocks; k = md_block_size * num_starting_blocks; } bits = 8 * mac_end_offset; if (!is_sslv3) { /* * Compute the initial HMAC block. For SSLv3, the padding and secret * bytes are included in |header| because they take more than a * single block. */ bits += 8 * md_block_size; memset(hmac_pad, 0, md_block_size); if (!ossl_assert(mac_secret_length <= sizeof(hmac_pad))) return 0; 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); } if (length_is_big_endian) { memset(length_bytes, 0, md_length_size - 4); length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); length_bytes[md_length_size - 1] = (unsigned char)bits; } else { memset(length_bytes, 0, md_length_size); length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); length_bytes[md_length_size - 8] = (unsigned char)bits; } if (k > 0) { if (is_sslv3) { size_t overhang; /* * The SSLv3 header is larger than a single block. overhang is * the number of bytes beyond a single block that the header * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no * ciphersuites in SSLv3 that are not SHA1 or MD5 based and * therefore we can be confident that the header_length will be * greater than |md_block_size|. However we add a sanity check just * in case */ if (header_length <= md_block_size) { /* Should never happen */ return 0; } overhang = header_length - md_block_size; md_transform(md_state.c, header); memcpy(first_block, header + md_block_size, overhang); memcpy(first_block + overhang, data, md_block_size - overhang); md_transform(md_state.c, first_block); for (i = 1; i < k / md_block_size - 1; i++) md_transform(md_state.c, data + md_block_size * i - overhang); } else { /* 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 + variance_blocks; i++) { unsigned char block[MAX_HASH_BLOCK_SIZE]; unsigned char is_block_a = constant_time_eq_8_s(i, index_a); unsigned char is_block_b = constant_time_eq_8_s(i, index_b); for (j = 0; j < md_block_size; j++) { unsigned char b = 0, is_past_c, is_past_cp1; if (k < header_length) b = header[k]; else if (k < data_plus_mac_plus_padding_size + header_length) b = data[k - header_length]; k++; is_past_c = is_block_a & constant_time_ge_8_s(j, c); is_past_cp1 = is_block_a & constant_time_ge_8_s(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 block contains 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; } md_ctx = EVP_MD_CTX_new(); if (md_ctx == NULL) goto err; if (EVP_DigestInit_ex(md_ctx, EVP_MD_CTX_md(ctx), NULL /* engine */ ) <= 0) goto err; if (is_sslv3) { /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ memset(hmac_pad, 0x5c, sslv3_pad_length); if (EVP_DigestUpdate(md_ctx, mac_secret, mac_secret_length) <= 0 || EVP_DigestUpdate(md_ctx, hmac_pad, sslv3_pad_length) <= 0 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0) goto err; } else { /* Complete the HMAC in the standard manner. */ for (i = 0; i < md_block_size; i++) hmac_pad[i] ^= 0x6a; if (EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size) <= 0 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0) goto err; } /* TODO(size_t): Convert me */ ret = EVP_DigestFinal(md_ctx, md_out, &md_out_size_u); if (ret && md_out_size) *md_out_size = md_out_size_u; EVP_MD_CTX_free(md_ctx); return 1; err: EVP_MD_CTX_free(md_ctx); return 0; }