pigweed / third_party / boringssl / boringssl / 17cf2cb1d226b0ba2401304242df7ddd3b6f1ff2 / . / crypto / cipher / tls_cbc.c

/* ==================================================================== | |

* 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 | |

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* 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 | |

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* 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 | |

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* ==================================================================== | |

* | |

* 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; | |

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. */ | |

unsigned 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); | |

} | |

unsigned rotate_offset = 0; | |

uint8_t mac_started = 0; | |

OPENSSL_memset(rotated_mac, 0, md_size); | |

for (unsigned i = scan_start, j = 0; i < orig_len; i++, j++) { | |

if (j >= md_size) { | |

j -= md_size; | |

} | |

unsigned is_mac_start = constant_time_eq(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 (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 (unsigned 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) | |

/* 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; | |

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 (i = 0; i < md_block_size; i++) { | |

hmac_pad[i] ^= 0x36; | |

} | |

md_transform(md_state.c, hmac_pad); | |

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. */ | |

OPENSSL_memcpy(first_block, header, 13); | |

OPENSSL_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); | |

} | |

} | |

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 (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; | |

} |