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 static void 52 signature_compute_hmac_md5(const u_int8_t *text, int text_len, unsigned char *key, 53 unsigned int key_len, u_int8_t *digest) 54 { 55 MD5_CTX context; 56 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */ 57 unsigned char k_opad[65]; /* outer padding - key XORd with opad */ 58 unsigned char tk[16]; 59 int i; 60 61 /* if key is longer than 64 bytes reset it to key=MD5(key) */ 62 if (key_len > 64) { 63 64 MD5_CTX tctx; 65 66 MD5_Init(&tctx); 67 MD5_Update(&tctx, key, key_len); 68 MD5_Final(tk, &tctx); 69 70 key = tk; 71 key_len = 16; 72 } 73 74 /* 75 * the HMAC_MD5 transform looks like: 76 * 77 * MD5(K XOR opad, MD5(K XOR ipad, text)) 78 * 79 * where K is an n byte key 80 * ipad is the byte 0x36 repeated 64 times 81 * opad is the byte 0x5c repeated 64 times 82 * and text is the data being protected 83 */ 84 85 /* start out by storing key in pads */ 86 memset(k_ipad, 0, sizeof k_ipad); 87 memset(k_opad, 0, sizeof k_opad); 88 memcpy(k_ipad, key, key_len); 89 memcpy(k_opad, key, key_len); 90 91 /* XOR key with ipad and opad values */ 92 for (i=0; i<64; i++) { 93 k_ipad[i] ^= 0x36; 94 k_opad[i] ^= 0x5c; 95 } 96 97 /* 98 * perform inner MD5 99 */ 100 MD5_Init(&context); /* init context for 1st pass */ 101 MD5_Update(&context, k_ipad, 64); /* start with inner pad */ 102 MD5_Update(&context, text, text_len); /* then text of datagram */ 103 MD5_Final(digest, &context); /* finish up 1st pass */ 104 105 /* 106 * perform outer MD5 107 */ 108 MD5_Init(&context); /* init context for 2nd pass */ 109 MD5_Update(&context, k_opad, 64); /* start with outer pad */ 110 MD5_Update(&context, digest, 16); /* then results of 1st hash */ 111 MD5_Final(digest, &context); /* finish up 2nd pass */ 112 } 113 #endif 114 115 #ifdef HAVE_LIBCRYPTO 116 /* 117 * Verify a cryptographic signature of the packet. 118 * Currently only MD5 is supported. 119 */ 120 int 121 signature_verify (const u_char *pptr, u_int plen, u_char *sig_ptr) 122 { 123 u_int8_t rcvsig[16]; 124 u_int8_t sig[16]; 125 unsigned int i; 126 127 /* 128 * Save the signature before clearing it. 129 */ 130 memcpy(rcvsig, sig_ptr, sizeof(rcvsig)); 131 memset(sig_ptr, 0, sizeof(rcvsig)); 132 133 if (!sigsecret) { 134 return (CANT_CHECK_SIGNATURE); 135 } 136 137 signature_compute_hmac_md5(pptr, plen, (unsigned char *)sigsecret, 138 strlen(sigsecret), sig); 139 140 if (memcmp(rcvsig, sig, sizeof(sig)) == 0) { 141 return (SIGNATURE_VALID); 142 143 } else { 144 145 for (i = 0; i < sizeof(sig); ++i) { 146 (void)printf("%02x", sig[i]); 147 } 148 149 return (SIGNATURE_INVALID); 150 } 151 } 152 #endif 153 154 /* 155 * Local Variables: 156 * c-style: whitesmith 157 * c-basic-offset: 4 158 * End: 159 */ 160