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@gredler.at)
16 */
17
18 #include <config.h>
19
20 #include "netdissect-stdinc.h"
21
22 #include <string.h>
23 #include <stdlib.h>
24
25 #include "netdissect.h"
26 #include "signature.h"
27 #include "diag-control.h"
28
29 #ifdef HAVE_LIBCRYPTO
30 #include <openssl/md5.h>
31 #endif
32
33 const struct tok signature_check_values[] = {
34 { SIGNATURE_VALID, "valid"},
35 { SIGNATURE_INVALID, "invalid"},
36 { CANT_ALLOCATE_COPY, "can't allocate memory"},
37 { CANT_CHECK_SIGNATURE, "unchecked"},
38 { 0, NULL }
39 };
40
41
42 #ifdef HAVE_LIBCRYPTO
43 /*
44 * Compute a HMAC MD5 sum.
45 * Taken from rfc2104, Appendix.
46 */
47 DIAG_OFF_DEPRECATION
48 static void
signature_compute_hmac_md5(const uint8_t * text,int text_len,unsigned char * key,unsigned int key_len,uint8_t * digest)49 signature_compute_hmac_md5(const uint8_t *text, int text_len, unsigned char *key,
50 unsigned int key_len, uint8_t *digest)
51 {
52 MD5_CTX context;
53 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */
54 unsigned char k_opad[65]; /* outer padding - key XORd with opad */
55 unsigned char tk[16];
56 int i;
57
58 /* if key is longer than 64 bytes reset it to key=MD5(key) */
59 if (key_len > 64) {
60
61 MD5_CTX tctx;
62
63 MD5_Init(&tctx);
64 MD5_Update(&tctx, key, key_len);
65 MD5_Final(tk, &tctx);
66
67 key = tk;
68 key_len = 16;
69 }
70
71 /*
72 * the HMAC_MD5 transform looks like:
73 *
74 * MD5(K XOR opad, MD5(K XOR ipad, text))
75 *
76 * where K is an n byte key
77 * ipad is the byte 0x36 repeated 64 times
78 * opad is the byte 0x5c repeated 64 times
79 * and text is the data being protected
80 */
81
82 /* start out by storing key in pads */
83 memset(k_ipad, 0, sizeof(k_ipad));
84 memset(k_opad, 0, sizeof(k_opad));
85 memcpy(k_ipad, key, key_len);
86 memcpy(k_opad, key, key_len);
87
88 /* XOR key with ipad and opad values */
89 for (i=0; i<64; i++) {
90 k_ipad[i] ^= 0x36;
91 k_opad[i] ^= 0x5c;
92 }
93
94 /*
95 * perform inner MD5
96 */
97 MD5_Init(&context); /* init context for 1st pass */
98 MD5_Update(&context, k_ipad, 64); /* start with inner pad */
99 MD5_Update(&context, text, text_len); /* then text of datagram */
100 MD5_Final(digest, &context); /* finish up 1st pass */
101
102 /*
103 * perform outer MD5
104 */
105 MD5_Init(&context); /* init context for 2nd pass */
106 MD5_Update(&context, k_opad, 64); /* start with outer pad */
107 MD5_Update(&context, digest, 16); /* then results of 1st hash */
108 MD5_Final(digest, &context); /* finish up 2nd pass */
109 }
110 DIAG_ON_DEPRECATION
111
112 /*
113 * Verify a cryptographic signature of the packet.
114 * Currently only MD5 is supported.
115 */
116 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)117 signature_verify(netdissect_options *ndo, const u_char *pptr, u_int plen,
118 const u_char *sig_ptr, void (*clear_rtn)(void *),
119 const void *clear_arg)
120 {
121 uint8_t *packet_copy, *sig_copy;
122 uint8_t sig[16];
123 unsigned int i;
124
125 if (!ndo->ndo_sigsecret) {
126 return (CANT_CHECK_SIGNATURE);
127 }
128
129 /*
130 * Do we have all the packet data to be checked?
131 */
132 if (!ND_TTEST_LEN(pptr, plen)) {
133 /* No. */
134 return (CANT_CHECK_SIGNATURE);
135 }
136
137 /*
138 * Do we have the entire signature to check?
139 */
140 if (!ND_TTEST_LEN(sig_ptr, sizeof(sig))) {
141 /* No. */
142 return (CANT_CHECK_SIGNATURE);
143 }
144 if (sig_ptr + sizeof(sig) > pptr + plen) {
145 /* No. */
146 return (CANT_CHECK_SIGNATURE);
147 }
148
149 /*
150 * Make a copy of the packet, so we don't overwrite the original.
151 */
152 packet_copy = malloc(plen);
153 if (packet_copy == NULL) {
154 return (CANT_ALLOCATE_COPY);
155 }
156
157 memcpy(packet_copy, pptr, plen);
158
159 /*
160 * Clear the signature in the copy.
161 */
162 sig_copy = packet_copy + (sig_ptr - pptr);
163 memset(sig_copy, 0, sizeof(sig));
164
165 /*
166 * Clear anything else that needs to be cleared in the copy.
167 * Our caller is assumed to have vetted the clear_arg pointer.
168 */
169 (*clear_rtn)((void *)(packet_copy + ((const uint8_t *)clear_arg - pptr)));
170
171 /*
172 * Compute the signature.
173 */
174 signature_compute_hmac_md5(packet_copy, plen,
175 (unsigned char *)ndo->ndo_sigsecret,
176 strlen(ndo->ndo_sigsecret), sig);
177
178 /*
179 * Free the copy.
180 */
181 free(packet_copy);
182
183 /*
184 * Does the computed signature match the signature in the packet?
185 */
186 if (memcmp(sig_ptr, sig, sizeof(sig)) == 0) {
187 /* Yes. */
188 return (SIGNATURE_VALID);
189 } else {
190 /* No - print the computed signature. */
191 for (i = 0; i < sizeof(sig); ++i) {
192 ND_PRINT("%02x", sig[i]);
193 }
194
195 return (SIGNATURE_INVALID);
196 }
197 }
198 #else
199 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_)200 signature_verify(netdissect_options *ndo _U_, const u_char *pptr _U_,
201 u_int plen _U_, const u_char *sig_ptr _U_,
202 void (*clear_rtn)(void *) _U_, const void *clear_arg _U_)
203 {
204 return (CANT_CHECK_SIGNATURE);
205 }
206 #endif
207