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
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
|
/*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that: (1) source code
* distributions retain the above copyright notice and this paragraph
* in its entirety, and (2) distributions including binary code include
* the above copyright notice and this paragraph in its entirety in
* the documentation or other materials provided with the distribution.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND
* WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
* LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE.
*
* Functions for signature and digest verification.
*
* Original code by Hannes Gredler (hannes@gredler.at)
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "netdissect-stdinc.h"
#include <string.h>
#include <stdlib.h>
#include "netdissect.h"
#include "signature.h"
#include "diag-control.h"
#ifdef HAVE_LIBCRYPTO
#include <openssl/md5.h>
#endif
const struct tok signature_check_values[] = {
{ SIGNATURE_VALID, "valid"},
{ SIGNATURE_INVALID, "invalid"},
{ CANT_ALLOCATE_COPY, "can't allocate memory"},
{ CANT_CHECK_SIGNATURE, "unchecked"},
{ 0, NULL }
};
#ifdef HAVE_LIBCRYPTO
/*
* Compute a HMAC MD5 sum.
* Taken from rfc2104, Appendix.
*/
DIAG_OFF_DEPRECATION
static void
signature_compute_hmac_md5(const uint8_t *text, int text_len, unsigned char *key,
unsigned int key_len, uint8_t *digest)
{
MD5_CTX context;
unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */
unsigned char k_opad[65]; /* outer padding - key XORd with opad */
unsigned char tk[16];
int i;
/* if key is longer than 64 bytes reset it to key=MD5(key) */
if (key_len > 64) {
MD5_CTX tctx;
MD5_Init(&tctx);
MD5_Update(&tctx, key, key_len);
MD5_Final(tk, &tctx);
key = tk;
key_len = 16;
}
/*
* the HMAC_MD5 transform looks like:
*
* MD5(K XOR opad, MD5(K XOR ipad, text))
*
* where K is an n byte key
* ipad is the byte 0x36 repeated 64 times
* opad is the byte 0x5c repeated 64 times
* and text is the data being protected
*/
/* start out by storing key in pads */
memset(k_ipad, 0, sizeof(k_ipad));
memset(k_opad, 0, sizeof(k_opad));
memcpy(k_ipad, key, key_len);
memcpy(k_opad, key, key_len);
/* XOR key with ipad and opad values */
for (i=0; i<64; i++) {
k_ipad[i] ^= 0x36;
k_opad[i] ^= 0x5c;
}
/*
* perform inner MD5
*/
MD5_Init(&context); /* init context for 1st pass */
MD5_Update(&context, k_ipad, 64); /* start with inner pad */
MD5_Update(&context, text, text_len); /* then text of datagram */
MD5_Final(digest, &context); /* finish up 1st pass */
/*
* perform outer MD5
*/
MD5_Init(&context); /* init context for 2nd pass */
MD5_Update(&context, k_opad, 64); /* start with outer pad */
MD5_Update(&context, digest, 16); /* then results of 1st hash */
MD5_Final(digest, &context); /* finish up 2nd pass */
}
DIAG_ON_DEPRECATION
/*
* Verify a cryptographic signature of the packet.
* Currently only MD5 is supported.
*/
int
signature_verify(netdissect_options *ndo, const u_char *pptr, u_int plen,
const u_char *sig_ptr, void (*clear_rtn)(void *),
const void *clear_arg)
{
uint8_t *packet_copy, *sig_copy;
uint8_t sig[16];
unsigned int i;
if (!ndo->ndo_sigsecret) {
return (CANT_CHECK_SIGNATURE);
}
/*
* Do we have all the packet data to be checked?
*/
if (!ND_TTEST_LEN(pptr, plen)) {
/* No. */
return (CANT_CHECK_SIGNATURE);
}
/*
* Do we have the entire signature to check?
*/
if (!ND_TTEST_LEN(sig_ptr, sizeof(sig))) {
/* No. */
return (CANT_CHECK_SIGNATURE);
}
if (sig_ptr + sizeof(sig) > pptr + plen) {
/* No. */
return (CANT_CHECK_SIGNATURE);
}
/*
* Make a copy of the packet, so we don't overwrite the original.
*/
packet_copy = malloc(plen);
if (packet_copy == NULL) {
return (CANT_ALLOCATE_COPY);
}
memcpy(packet_copy, pptr, plen);
/*
* Clear the signature in the copy.
*/
sig_copy = packet_copy + (sig_ptr - pptr);
memset(sig_copy, 0, sizeof(sig));
/*
* Clear anything else that needs to be cleared in the copy.
* Our caller is assumed to have vetted the clear_arg pointer.
*/
(*clear_rtn)((void *)(packet_copy + ((const uint8_t *)clear_arg - pptr)));
/*
* Compute the signature.
*/
signature_compute_hmac_md5(packet_copy, plen,
(unsigned char *)ndo->ndo_sigsecret,
strlen(ndo->ndo_sigsecret), sig);
/*
* Free the copy.
*/
free(packet_copy);
/*
* Does the computed signature match the signature in the packet?
*/
if (memcmp(sig_ptr, sig, sizeof(sig)) == 0) {
/* Yes. */
return (SIGNATURE_VALID);
} else {
/* No - print the computed signature. */
for (i = 0; i < sizeof(sig); ++i) {
ND_PRINT("%02x", sig[i]);
}
return (SIGNATURE_INVALID);
}
}
#else
int
signature_verify(netdissect_options *ndo _U_, const u_char *pptr _U_,
u_int plen _U_, const u_char *sig_ptr _U_,
void (*clear_rtn)(void *) _U_, const void *clear_arg _U_)
{
return (CANT_CHECK_SIGNATURE);
}
#endif
|
