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 #define NETDISSECT_REWORKED 19 #ifdef HAVE_CONFIG_H 20 #include "config.h" 21 #endif 22 23 #include <tcpdump-stdinc.h> 24 25 #include <string.h> 26 27 #include "interface.h" 28 #include "signature.h" 29 30 #ifdef HAVE_LIBCRYPTO 31 #include <openssl/md5.h> 32 #endif 33 34 const struct tok signature_check_values[] = { 35 { SIGNATURE_VALID, "valid"}, 36 { SIGNATURE_INVALID, "invalid"}, 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 USES_APPLE_DEPRECATED_API 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 USES_APPLE_RST 111 #endif 112 113 #ifdef HAVE_LIBCRYPTO 114 /* 115 * Verify a cryptographic signature of the packet. 116 * Currently only MD5 is supported. 117 */ 118 int 119 signature_verify(netdissect_options *ndo, 120 const u_char *pptr, u_int plen, u_char *sig_ptr) 121 { 122 uint8_t rcvsig[16]; 123 uint8_t sig[16]; 124 unsigned int i; 125 126 /* 127 * Save the signature before clearing it. 128 */ 129 memcpy(rcvsig, sig_ptr, sizeof(rcvsig)); 130 memset(sig_ptr, 0, sizeof(rcvsig)); 131 132 if (!ndo->ndo_sigsecret) { 133 return (CANT_CHECK_SIGNATURE); 134 } 135 136 signature_compute_hmac_md5(pptr, plen, (unsigned char *)ndo->ndo_sigsecret, 137 strlen(ndo->ndo_sigsecret), sig); 138 139 if (memcmp(rcvsig, sig, sizeof(sig)) == 0) { 140 return (SIGNATURE_VALID); 141 142 } else { 143 144 for (i = 0; i < sizeof(sig); ++i) { 145 ND_PRINT((ndo, "%02x", sig[i])); 146 } 147 148 return (SIGNATURE_INVALID); 149 } 150 } 151 #endif 152 153 /* 154 * Local Variables: 155 * c-style: whitesmith 156 * c-basic-offset: 4 157 * End: 158 */ 159