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 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 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 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