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/*
* Copyright 2012-2018 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (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_locl.h"
#include "ssl_locl.h"
#include "internal/cryptlib.h"
#include <openssl/md5.h>
#include <openssl/sha.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
/*
* 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;
}