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openssl/ssl/s3_cbc.c
Matt Caswell 99ceb2d40c Add sanity check in ssl3_cbc_digest_record 
For SSLv3 the code assumes that |header_length| > |md_block_size|. Whilst
this is true for all SSLv3 ciphersuites, this fact is far from obvious by
looking at the code. If this were not the case then an integer overflow
would occur, leading to a subsequent buffer overflow. Therefore I have
added an explicit sanity check to ensure header_length is always valid.
Thanks to Kevin Wojtysiak (Int3 Solutions) and Paramjot Oberoi (Int3
Solutions) for reporting this issue.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(cherry picked from commit 29b0a15a48)
2015-04-30 23:21:53 +01:00

805 lines
30 KiB
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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 ((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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