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
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
|
/*
chronyd/chronyc - Programs for keeping computer clocks accurate.
**********************************************************************
* Copyright (C) Miroslav Lichvar 2020
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
**********************************************************************
=======================================================================
NTS Authenticator and Encrypted Extension Fields extension field
*/
#include "config.h"
#include "sysincl.h"
#include "nts_ntp_auth.h"
#include "logging.h"
#include "ntp_ext.h"
#include "nts_ntp.h"
#include "siv.h"
#include "util.h"
struct AuthHeader {
uint16_t nonce_length;
uint16_t ciphertext_length;
};
/* ================================================== */
static int
get_padding_length(int length)
{
return length % 4U ? 4 - length % 4U : 0;
}
/* ================================================== */
static int
get_padded_length(int length)
{
return length + get_padding_length(length);
}
/* ================================================== */
int
NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
const unsigned char *nonce, int max_nonce_length,
const unsigned char *plaintext, int plaintext_length,
int min_ef_length)
{
int auth_length, ciphertext_length, assoc_length, nonce_length, max_siv_nonce_length;
int nonce_padding, ciphertext_padding, additional_padding;
unsigned char *ciphertext, *body;
struct AuthHeader *header;
assert(sizeof (*header) == 4);
if (max_nonce_length <= 0 || plaintext_length < 0) {
DEBUG_LOG("Invalid nonce/plaintext length");
return 0;
}
assoc_length = info->length;
max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
nonce_length = MIN(max_nonce_length, max_siv_nonce_length);
ciphertext_length = SIV_GetTagLength(siv) + plaintext_length;
nonce_padding = get_padding_length(nonce_length);
ciphertext_padding = get_padding_length(ciphertext_length);
min_ef_length = get_padded_length(min_ef_length);
auth_length = sizeof (*header) + nonce_length + nonce_padding +
ciphertext_length + ciphertext_padding;
additional_padding = MAX(min_ef_length - auth_length - 4, 0);
additional_padding = MAX(MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) -
nonce_length - nonce_padding, additional_padding);
auth_length += additional_padding;
if (!NEF_AddBlankField(packet, info, NTP_EF_NTS_AUTH_AND_EEF, auth_length,
(void **)&header)) {
DEBUG_LOG("Could not add EF");
return 0;
}
header->nonce_length = htons(nonce_length);
header->ciphertext_length = htons(ciphertext_length);
body = (unsigned char *)(header + 1);
ciphertext = body + nonce_length + nonce_padding;
if ((unsigned char *)header + auth_length !=
ciphertext + ciphertext_length + ciphertext_padding + additional_padding)
assert(0);
memcpy(body, nonce, nonce_length);
memset(body + nonce_length, 0, nonce_padding);
if (!SIV_Encrypt(siv, nonce, nonce_length, packet, assoc_length,
plaintext, plaintext_length, ciphertext, ciphertext_length)) {
DEBUG_LOG("SIV encrypt failed");
info->length = assoc_length;
info->ext_fields--;
return 0;
}
memset(ciphertext + ciphertext_length, 0, ciphertext_padding + additional_padding);
return 1;
}
/* ================================================== */
int
NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, int ef_start,
unsigned char *plaintext, int buffer_length, int *plaintext_length)
{
int siv_tag_length, max_siv_nonce_length, nonce_length, ciphertext_length;
unsigned char *nonce, *ciphertext;
int ef_type, ef_body_length;
void *ef_body;
struct AuthHeader *header;
if (buffer_length < 0)
return 0;
if (!NEF_ParseField(packet, info->length, ef_start,
NULL, &ef_type, &ef_body, &ef_body_length))
return 0;
if (ef_type != NTP_EF_NTS_AUTH_AND_EEF || ef_body_length < sizeof (*header))
return 0;
header = ef_body;
nonce_length = ntohs(header->nonce_length);
ciphertext_length = ntohs(header->ciphertext_length);
if (get_padded_length(nonce_length) +
get_padded_length(ciphertext_length) > ef_body_length)
return 0;
nonce = (unsigned char *)(header + 1);
ciphertext = nonce + get_padded_length(nonce_length);
max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
siv_tag_length = SIV_GetTagLength(siv);
if (nonce_length < 1 ||
ciphertext_length < siv_tag_length ||
ciphertext_length - siv_tag_length > buffer_length) {
DEBUG_LOG("Unexpected nonce/ciphertext length");
return 0;
}
if (sizeof (*header) + MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) +
get_padded_length(ciphertext_length) > ef_body_length) {
DEBUG_LOG("Missing padding");
return 0;
}
*plaintext_length = ciphertext_length - siv_tag_length;
assert(*plaintext_length >= 0);
if (!SIV_Decrypt(siv, nonce, nonce_length, packet, ef_start,
ciphertext, ciphertext_length, plaintext, *plaintext_length)) {
DEBUG_LOG("SIV decrypt failed");
return 0;
}
return 1;
}
|
