1 /*
2 * Redistribution and use in source and binary forms, with or without
3 * modification, are permitted provided that: (1) source code
4 * distributions retain the above copyright notice and this paragraph
5 * in its entirety, and (2) distributions including binary code include
6 * the above copyright notice and this paragraph in its entirety in
7 * the documentation or other materials provided with the distribution.
8 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND
9 * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
10 * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
11 * FOR A PARTICULAR PURPOSE.
12 *
13 * Functions for signature and digest verification.
14 *
15 * Original code by Hannes Gredler (hannes@juniper.net)
16 */
17
18 #ifndef lint
19 static const char rcsid[] _U_ =
20 "@(#) $Header: /tcpdump/master/tcpdump/signature.c,v 1.2 2008-09-22 20:22:10 guy Exp $ (LBL)";
21 #endif
22
23 #ifdef HAVE_CONFIG_H
24 #include "config.h"
25 #endif
26
27 #include <tcpdump-stdinc.h>
28
29 #include <string.h>
30
31 #include "interface.h"
32 #include "signature.h"
33
34 #ifdef HAVE_LIBCRYPTO
35 #include <openssl/md5.h>
36 #endif
37
38 const struct tok signature_check_values[] = {
39 { SIGNATURE_VALID, "valid"},
40 { SIGNATURE_INVALID, "invalid"},
41 { CANT_CHECK_SIGNATURE, "unchecked"},
42 { 0, NULL }
43 };
44
45
46 #ifdef HAVE_LIBCRYPTO
47 /*
48 * Compute a HMAC MD5 sum.
49 * Taken from rfc2104, Appendix.
50 */
51 USES_APPLE_DEPRECATED_API
52 static void
signature_compute_hmac_md5(const u_int8_t * text,int text_len,unsigned char * key,unsigned int key_len,u_int8_t * digest)53 signature_compute_hmac_md5(const u_int8_t *text, int text_len, unsigned char *key,
54 unsigned int key_len, u_int8_t *digest)
55 {
56 MD5_CTX context;
57 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */
58 unsigned char k_opad[65]; /* outer padding - key XORd with opad */
59 unsigned char tk[16];
60 int i;
61
62 /* if key is longer than 64 bytes reset it to key=MD5(key) */
63 if (key_len > 64) {
64
65 MD5_CTX tctx;
66
67 MD5_Init(&tctx);
68 MD5_Update(&tctx, key, key_len);
69 MD5_Final(tk, &tctx);
70
71 key = tk;
72 key_len = 16;
73 }
74
75 /*
76 * the HMAC_MD5 transform looks like:
77 *
78 * MD5(K XOR opad, MD5(K XOR ipad, text))
79 *
80 * where K is an n byte key
81 * ipad is the byte 0x36 repeated 64 times
82 * opad is the byte 0x5c repeated 64 times
83 * and text is the data being protected
84 */
85
86 /* start out by storing key in pads */
87 memset(k_ipad, 0, sizeof k_ipad);
88 memset(k_opad, 0, sizeof k_opad);
89 memcpy(k_ipad, key, key_len);
90 memcpy(k_opad, key, key_len);
91
92 /* XOR key with ipad and opad values */
93 for (i=0; i<64; i++) {
94 k_ipad[i] ^= 0x36;
95 k_opad[i] ^= 0x5c;
96 }
97
98 /*
99 * perform inner MD5
100 */
101 MD5_Init(&context); /* init context for 1st pass */
102 MD5_Update(&context, k_ipad, 64); /* start with inner pad */
103 MD5_Update(&context, text, text_len); /* then text of datagram */
104 MD5_Final(digest, &context); /* finish up 1st pass */
105
106 /*
107 * perform outer MD5
108 */
109 MD5_Init(&context); /* init context for 2nd pass */
110 MD5_Update(&context, k_opad, 64); /* start with outer pad */
111 MD5_Update(&context, digest, 16); /* then results of 1st hash */
112 MD5_Final(digest, &context); /* finish up 2nd pass */
113 }
114 USES_APPLE_RST
115 #endif
116
117 #ifdef HAVE_LIBCRYPTO
118 /*
119 * Verify a cryptographic signature of the packet.
120 * Currently only MD5 is supported.
121 */
122 int
signature_verify(const u_char * pptr,u_int plen,u_char * sig_ptr)123 signature_verify (const u_char *pptr, u_int plen, u_char *sig_ptr)
124 {
125 u_int8_t rcvsig[16];
126 u_int8_t sig[16];
127 unsigned int i;
128
129 /*
130 * Save the signature before clearing it.
131 */
132 memcpy(rcvsig, sig_ptr, sizeof(rcvsig));
133 memset(sig_ptr, 0, sizeof(rcvsig));
134
135 if (!sigsecret) {
136 return (CANT_CHECK_SIGNATURE);
137 }
138
139 signature_compute_hmac_md5(pptr, plen, (unsigned char *)sigsecret,
140 strlen(sigsecret), sig);
141
142 if (memcmp(rcvsig, sig, sizeof(sig)) == 0) {
143 return (SIGNATURE_VALID);
144
145 } else {
146
147 for (i = 0; i < sizeof(sig); ++i) {
148 (void)printf("%02x", sig[i]);
149 }
150
151 return (SIGNATURE_INVALID);
152 }
153 }
154 #endif
155
156 /*
157 * Local Variables:
158 * c-style: whitesmith
159 * c-basic-offset: 4
160 * End:
161 */
162