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 #include <sys/cdefs.h> 19 #ifndef lint 20 #if 0 21 static const char rcsid[] _U_ = 22 "@(#) Header: /tcpdump/master/tcpdump/signature.c,v 1.2 2008-09-22 20:22:10 guy Exp (LBL)"; 23 #else 24 __RCSID("$NetBSD: signature.c,v 1.2 2010/12/05 05:11:31 christos Exp $"); 25 #endif 26 #endif 27 28 #ifdef HAVE_CONFIG_H 29 #include "config.h" 30 #endif 31 32 #include <tcpdump-stdinc.h> 33 34 #include <string.h> 35 36 #include "interface.h" 37 #include "signature.h" 38 39 #ifdef HAVE_LIBCRYPTO 40 #include <openssl/md5.h> 41 #endif 42 43 const struct tok signature_check_values[] = { 44 { SIGNATURE_VALID, "valid"}, 45 { SIGNATURE_INVALID, "invalid"}, 46 { CANT_CHECK_SIGNATURE, "unchecked"}, 47 { 0, NULL } 48 }; 49 50 51 #ifdef HAVE_LIBCRYPTO 52 /* 53 * Compute a HMAC MD5 sum. 54 * Taken from rfc2104, Appendix. 55 */ 56 static void 57 signature_compute_hmac_md5(const u_int8_t *text, int text_len, unsigned char *key, 58 unsigned int key_len, u_int8_t *digest) 59 { 60 MD5_CTX context; 61 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */ 62 unsigned char k_opad[65]; /* outer padding - key XORd with opad */ 63 unsigned char tk[16]; 64 int i; 65 66 /* if key is longer than 64 bytes reset it to key=MD5(key) */ 67 if (key_len > 64) { 68 69 MD5_CTX tctx; 70 71 MD5_Init(&tctx); 72 MD5_Update(&tctx, key, key_len); 73 MD5_Final(tk, &tctx); 74 75 key = tk; 76 key_len = 16; 77 } 78 79 /* 80 * the HMAC_MD5 transform looks like: 81 * 82 * MD5(K XOR opad, MD5(K XOR ipad, text)) 83 * 84 * where K is an n byte key 85 * ipad is the byte 0x36 repeated 64 times 86 * opad is the byte 0x5c repeated 64 times 87 * and text is the data being protected 88 */ 89 90 /* start out by storing key in pads */ 91 memset(k_ipad, 0, sizeof k_ipad); 92 memset(k_opad, 0, sizeof k_opad); 93 memcpy(k_ipad, key, key_len); 94 memcpy(k_opad, key, key_len); 95 96 /* XOR key with ipad and opad values */ 97 for (i=0; i<64; i++) { 98 k_ipad[i] ^= 0x36; 99 k_opad[i] ^= 0x5c; 100 } 101 102 /* 103 * perform inner MD5 104 */ 105 MD5_Init(&context); /* init context for 1st pass */ 106 MD5_Update(&context, k_ipad, 64); /* start with inner pad */ 107 MD5_Update(&context, text, text_len); /* then text of datagram */ 108 MD5_Final(digest, &context); /* finish up 1st pass */ 109 110 /* 111 * perform outer MD5 112 */ 113 MD5_Init(&context); /* init context for 2nd pass */ 114 MD5_Update(&context, k_opad, 64); /* start with outer pad */ 115 MD5_Update(&context, digest, 16); /* then results of 1st hash */ 116 MD5_Final(digest, &context); /* finish up 2nd pass */ 117 } 118 #endif 119 120 #ifdef HAVE_LIBCRYPTO 121 /* 122 * Verify a cryptographic signature of the packet. 123 * Currently only MD5 is supported. 124 */ 125 int 126 signature_verify (const u_char *pptr, u_int plen, u_char *sig_ptr) 127 { 128 u_int8_t rcvsig[16]; 129 u_int8_t sig[16]; 130 unsigned int i; 131 132 /* 133 * Save the signature before clearing it. 134 */ 135 memcpy(rcvsig, sig_ptr, sizeof(rcvsig)); 136 memset(sig_ptr, 0, sizeof(rcvsig)); 137 138 if (!sigsecret) { 139 return (CANT_CHECK_SIGNATURE); 140 } 141 142 signature_compute_hmac_md5(pptr, plen, (unsigned char *)sigsecret, 143 strlen(sigsecret), sig); 144 145 if (memcmp(rcvsig, sig, sizeof(sig)) == 0) { 146 return (SIGNATURE_VALID); 147 148 } else { 149 150 for (i = 0; i < sizeof(sig); ++i) { 151 (void)printf("%02x", sig[i]); 152 } 153 154 return (SIGNATURE_INVALID); 155 } 156 } 157 #endif 158 159 /* 160 * Local Variables: 161 * c-style: whitesmith 162 * c-basic-offset: 4 163 * End: 164 */ 165