1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
|
/*
* Copyright (C) 2000-2013 Free Software Foundation, Inc.
* Copyright (C) 2013 Nikos Mavrogiannopoulos
* Copyright (C) 2017-2018 Red Hat, Inc.
*
* Author: Nikos Mavrogiannopoulos
*
* This file is part of GnuTLS.
*
* The GnuTLS is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* as published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>
*
*/
#include "gnutls_int.h"
#include "cipher.h"
static void dummy_wait(record_parameters_st *params, const uint8_t *data,
size_t data_size, unsigned int mac_data,
unsigned int max_mac_data)
{
/* this hack is only needed on CBC ciphers when Encrypt-then-MAC mode
* is not supported by the peer. */
unsigned v;
unsigned int tag_size =
_gnutls_auth_cipher_tag_len(¶ms->read.ctx.tls12);
unsigned hash_block = _gnutls_mac_block_size(params->mac);
/* force additional hash compression function evaluations to prevent timing
* attacks that distinguish between wrong-mac + correct pad, from wrong-mac + incorrect pad.
*/
if (params->mac && params->mac->id == GNUTLS_MAC_SHA384)
/* v = 1 for the hash function padding + 16 for message length */
v = 17;
else /* v = 1 for the hash function padding + 8 for message length */
v = 9;
if (hash_block > 0) {
int max_blocks =
(max_mac_data + v + hash_block - 1) / hash_block;
int hashed_blocks =
(mac_data + v + hash_block - 1) / hash_block;
unsigned to_hash;
max_blocks -= hashed_blocks;
if (max_blocks < 1)
return;
to_hash = max_blocks * hash_block;
if ((unsigned)to_hash + 1 + tag_size < data_size) {
_gnutls_auth_cipher_add_auth(
¶ms->read.ctx.tls12,
data + data_size - tag_size - to_hash - 1,
to_hash);
}
}
}
/* Verifies the CBC HMAC. That's a special case as it tries to avoid
* any leaks which could make CBC ciphersuites without EtM usable as an
* oracle to attacks.
*/
int cbc_mac_verify(gnutls_session_t session, record_parameters_st *params,
uint8_t preamble[MAX_PREAMBLE_SIZE], content_type_t type,
uint64_t sequence, const uint8_t *data, size_t data_size,
size_t tag_size)
{
int ret;
const version_entry_st *ver = get_version(session);
unsigned int tmp_pad_failed = 0;
unsigned int pad_failed = 0;
unsigned int pad, i, length;
const uint8_t *tag_ptr = NULL;
unsigned preamble_size;
uint8_t tag[MAX_HASH_SIZE];
#ifdef ENABLE_SSL3
unsigned blocksize = _gnutls_cipher_get_block_size(params->cipher);
#endif
pad = data[data_size - 1]; /* pad */
/* Check the padding bytes (TLS 1.x).
* Note that we access all 256 bytes of ciphertext for padding check
* because there is a timing channel in that memory access (in certain CPUs).
*/
#ifdef ENABLE_SSL3
if (ver->id == GNUTLS_SSL3) {
if (pad >= blocksize)
pad_failed = 1;
} else
#endif
{
for (i = 2; i <= MIN(256, data_size); i++) {
tmp_pad_failed |= (data[data_size - i] != pad);
pad_failed |= ((i <= (1 + pad)) & (tmp_pad_failed));
}
}
if (unlikely(pad_failed != 0 ||
(1 + pad > ((int)data_size - tag_size)))) {
/* We do not fail here. We check below for the
* the pad_failed. If zero means success.
*/
pad_failed = 1;
pad = 0;
}
length = data_size - tag_size - pad - 1;
tag_ptr = &data[length];
/* Pass the type, version, length and plain through
* MAC.
*/
preamble_size =
_gnutls_make_preamble(sequence, type, length, ver, preamble);
ret = _gnutls_auth_cipher_add_auth(¶ms->read.ctx.tls12, preamble,
preamble_size);
if (unlikely(ret < 0))
return gnutls_assert_val(ret);
ret = _gnutls_auth_cipher_add_auth(¶ms->read.ctx.tls12, data,
length);
if (unlikely(ret < 0))
return gnutls_assert_val(ret);
ret = _gnutls_auth_cipher_tag(¶ms->read.ctx.tls12, tag, tag_size);
if (unlikely(ret < 0))
return gnutls_assert_val(ret);
if (unlikely(gnutls_memcmp(tag, tag_ptr, tag_size) != 0 ||
pad_failed != 0)) {
/* HMAC was not the same. */
dummy_wait(params, data, data_size, length + preamble_size,
preamble_size + data_size - tag_size - 1);
return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
}
return length;
}
|
