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openssl/ssl/s3_cbc.c
Emilia Kasper 05627d57e5 Use CRYPTO_memcmp in s3_cbc.c 
Reviewed-by: Rich Salz <rsalz@openssl.org>
2015-06-08 15:04:28 +02:00

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/* ssl/s3_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
* 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 "../crypto/constant_time_locl.h"
#include "ssl_locl.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
/*-
* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
* record in |rec| by updating |rec->length| in constant time.
*
* block_size: the block size of the cipher used to encrypt the record.
* returns:
* 0: (in non-constant time) if the record is publicly invalid.
* 1: if the padding was valid
* -1: otherwise.
*/
int ssl3_cbc_remove_padding(const SSL *s,
SSL3_RECORD *rec,
unsigned block_size, unsigned mac_size)
{
unsigned padding_length, good;
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 > rec->length)
return 0;
padding_length = rec->data[rec->length - 1];
good = constant_time_ge(rec->length, padding_length + overhead);
/* SSLv3 requires that the padding is minimal. */
good &= constant_time_ge(block_size, padding_length + 1);
padding_length = good & (padding_length + 1);
rec->length -= padding_length;
rec->type |= padding_length << 8; /* kludge: pass padding length */
return constant_time_select_int(good, 1, -1);
}
/*-
* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
* record in |rec| in constant time and returns 1 if the padding is valid and
* -1 otherwise. It also removes any explicit IV from the start of the record
* without leaking any timing about whether there was enough space after the
* padding was removed.
*
* block_size: the block size of the cipher used to encrypt the record.
* returns:
* 0: (in non-constant time) if the record is publicly invalid.
* 1: if the padding was valid
* -1: otherwise.
*/
int tls1_cbc_remove_padding(const SSL *s,
SSL3_RECORD *rec,
unsigned block_size, unsigned mac_size)
{
unsigned padding_length, good, to_check, i;
const unsigned overhead = 1 /* padding length byte */ + mac_size;
/* Check if version requires explicit IV */
if (SSL_USE_EXPLICIT_IV(s)) {
/*
* These lengths are all public so we can test them in non-constant
* time.
*/
if (overhead + block_size > rec->length)
return 0;
/* We can now safely skip explicit IV */
rec->data += block_size;
rec->input += block_size;
rec->length -= block_size;
} else if (overhead > rec->length)
return 0;
padding_length = rec->data[rec->length - 1];
/*
* NB: if compression is in operation the first packet may not be of even
* length so the padding bug check cannot be performed. This bug
* workaround has been around since SSLeay so hopefully it is either
* fixed now or no buggy implementation supports compression [steve]
*/
if ((s->options & SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand) {
/* First packet is even in size, so check */
if ((CRYPTO_memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0", 8) == 0) &&
!(padding_length & 1)) {
s->s3->flags |= TLS1_FLAGS_TLS_PADDING_BUG;
}
if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) && padding_length > 0) {
padding_length--;
}
}
if (EVP_CIPHER_flags(s->enc_read_ctx->cipher) & EVP_CIPH_FLAG_AEAD_CIPHER) {
/* padding is already verified */
rec->length -= padding_length + 1;
return 1;
}
good = constant_time_ge(rec->length, 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 = 255; /* maximum amount of padding. */
if (to_check > rec->length - 1)
to_check = rec->length - 1;
for (i = 0; i < to_check; i++) {
unsigned char mask = constant_time_ge_8(padding_length, i);
unsigned char b = rec->data[rec->length - 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);
padding_length = good & (padding_length + 1);
rec->length -= padding_length;
rec->type |= padding_length << 8; /* kludge: pass padding length */
return constant_time_select_int(good, 1, -1);
}
/*-
* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
* constant time (independent of the concrete value of rec->length, which may
* vary within a 256-byte window).
*
* ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
* this function.
*
* On entry:
* rec->orig_len >= md_size
* md_size <= EVP_MAX_MD_SIZE
*
* If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation 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 ssl3_cbc_copy_mac(unsigned char *out,
const SSL3_RECORD *rec,
unsigned md_size, unsigned orig_len)
{
#if defined(CBC_MAC_ROTATE_IN_PLACE)
unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE];
unsigned char *rotated_mac;
#else
unsigned char rotated_mac[EVP_MAX_MD_SIZE];
#endif
/*
* mac_end is the index of |rec->data| just after the end of the MAC.
*/
unsigned mac_end = rec->length;
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 div_spoiler;
unsigned rotate_offset;
OPENSSL_assert(orig_len >= md_size);
OPENSSL_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);
/*
* div_spoiler contains a multiple of md_size that is used to cause the
* modulo operation to be constant time. Without this, the time varies
* based on the amount of padding when running on Intel chips at least.
* The aim of right-shifting md_size is so that the compiler doesn't
* figure out that it can remove div_spoiler as that would require it to
* prove that md_size is always even, which I hope is beyond it.
*/
div_spoiler = md_size >> 1;
div_spoiler <<= (sizeof(div_spoiler) - 1) * 8;
rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
memset(rotated_mac, 0, md_size);
for (i = scan_start, j = 0; i < orig_len; i++) {
unsigned char mac_started = constant_time_ge_8(i, mac_start);
unsigned char mac_ended = constant_time_ge_8(i, mac_end);
unsigned char b = rec->data[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 unsigned char *)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
}
/*
* 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);
}
#define LARGEST_DIGEST_CTX SHA_CTX
#ifndef OPENSSL_NO_SHA256
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);
}
}
# undef LARGEST_DIGEST_CTX
# define LARGEST_DIGEST_CTX SHA256_CTX
#endif
#ifndef OPENSSL_NO_SHA512
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
#endif
/*
* 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)
{
#ifdef OPENSSL_FIPS
if (FIPS_mode())
return 0;
#endif
switch (EVP_MD_CTX_type(ctx)) {
case NID_md5:
case NID_sha1:
#ifndef OPENSSL_NO_SHA256
case NID_sha224:
case NID_sha256:
#endif
#ifndef OPENSSL_NO_SHA512
case NID_sha384:
case NID_sha512:
#endif
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 preceeding 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. )
*/
void 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,
unsigned 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);
unsigned md_size, md_block_size = 64;
unsigned 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;
unsigned int 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];
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;
char length_is_big_endian = 1;
/*
* This is a, hopefully redundant, check that allows us to forget about
* many possible overflows later in this function.
*/
OPENSSL_assert(data_plus_mac_plus_padding_size < 1024 * 1024);
switch (EVP_MD_CTX_type(ctx)) {
case NID_md5:
MD5_Init((MD5_CTX *)md_state.c);
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:
SHA1_Init((SHA_CTX *)md_state.c);
md_final_raw = tls1_sha1_final_raw;
md_transform =
(void (*)(void *ctx, const unsigned char *block))SHA1_Transform;
md_size = 20;
break;
#ifndef OPENSSL_NO_SHA256
case NID_sha224:
SHA224_Init((SHA256_CTX *)md_state.c);
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:
SHA256_Init((SHA256_CTX *)md_state.c);
md_final_raw = tls1_sha256_final_raw;
md_transform =
(void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
md_size = 32;
break;
#endif
#ifndef OPENSSL_NO_SHA512
case NID_sha384:
SHA384_Init((SHA512_CTX *)md_state.c);
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:
SHA512_Init((SHA512_CTX *)md_state.c);
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;
#endif
default:
/*
* ssl3_cbc_record_digest_supported should have been called first to
* check that the hash function is supported.
*/
OPENSSL_assert(0);
if (md_out_size)
*md_out_size = -1;
return;
}
OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
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 six 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 : 6;
/*
* 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);
OPENSSL_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);
}
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) {
unsigned 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;
}
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(i, index_a);
unsigned char is_block_b = constant_time_eq_8(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(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);
EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */ );
if (is_sslv3) {
/* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
memset(hmac_pad, 0x5c, sslv3_pad_length);
EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length);
EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length);
EVP_DigestUpdate(&md_ctx, mac_out, md_size);
} else {
/* 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);
if (md_out_size)
*md_out_size = md_out_size_u;
EVP_MD_CTX_cleanup(&md_ctx);
}
#ifdef OPENSSL_FIPS
/*
* Due to the need to use EVP in FIPS mode we can't reimplement digests but
* we can ensure the number of blocks processed is equal for all cases by
* digesting additional data.
*/
void tls_fips_digest_extra(const EVP_CIPHER_CTX *cipher_ctx,
EVP_MD_CTX *mac_ctx, const unsigned char *data,
size_t data_len, size_t orig_len)
{
size_t block_size, digest_pad, blocks_data, blocks_orig;
if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE)
return;
block_size = EVP_MD_CTX_block_size(mac_ctx);
/*-
* We are in FIPS mode if we get this far so we know we have only SHA*
* digests and TLS to deal with.
* Minimum digest padding length is 17 for SHA384/SHA512 and 9
* otherwise.
* Additional header is 13 bytes. To get the number of digest blocks
* processed round up the amount of data plus padding to the nearest
* block length. Block length is 128 for SHA384/SHA512 and 64 otherwise.
* So we have:
* blocks = (payload_len + digest_pad + 13 + block_size - 1)/block_size
* equivalently:
* blocks = (payload_len + digest_pad + 12)/block_size + 1
* HMAC adds a constant overhead.
* We're ultimately only interested in differences so this becomes
* blocks = (payload_len + 29)/128
* for SHA384/SHA512 and
* blocks = (payload_len + 21)/64
* otherwise.
*/
digest_pad = block_size == 64 ? 21 : 29;
blocks_orig = (orig_len + digest_pad) / block_size;
blocks_data = (data_len + digest_pad) / block_size;
/*
* MAC enough blocks to make up the difference between the original and
* actual lengths plus one extra block to ensure this is never a no op.
* The "data" pointer should always have enough space to perform this
* operation as it is large enough for a maximum length TLS buffer.
*/
EVP_DigestSignUpdate(mac_ctx, data,
(blocks_orig - blocks_data + 1) * block_size);
}
#endif
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