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 __RCSID("$NetBSD: signature.c,v 1.5 2014/11/20 03:05:03 christos Exp $"); 21 #endif 22 23 #define NETDISSECT_REWORKED 24 #ifdef HAVE_CONFIG_H 25 #include "config.h" 26 #endif 27 28 #include <tcpdump-stdinc.h> 29 30 #include <string.h> 31 32 #include "interface.h" 33 #include "signature.h" 34 35 #ifdef HAVE_LIBCRYPTO 36 #include <openssl/md5.h> 37 #endif 38 39 const struct tok signature_check_values[] = { 40 { SIGNATURE_VALID, "valid"}, 41 { SIGNATURE_INVALID, "invalid"}, 42 { CANT_CHECK_SIGNATURE, "unchecked"}, 43 { 0, NULL } 44 }; 45 46 47 #ifdef HAVE_LIBCRYPTO 48 /* 49 * Compute a HMAC MD5 sum. 50 * Taken from rfc2104, Appendix. 51 */ 52 USES_APPLE_DEPRECATED_API 53 static void 54 signature_compute_hmac_md5(const uint8_t *text, int text_len, unsigned char *key, 55 unsigned int key_len, uint8_t *digest) 56 { 57 MD5_CTX context; 58 unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */ 59 unsigned char k_opad[65]; /* outer padding - key XORd with opad */ 60 unsigned char tk[16]; 61 int i; 62 63 /* if key is longer than 64 bytes reset it to key=MD5(key) */ 64 if (key_len > 64) { 65 66 MD5_CTX tctx; 67 68 MD5_Init(&tctx); 69 MD5_Update(&tctx, key, key_len); 70 MD5_Final(tk, &tctx); 71 72 key = tk; 73 key_len = 16; 74 } 75 76 /* 77 * the HMAC_MD5 transform looks like: 78 * 79 * MD5(K XOR opad, MD5(K XOR ipad, text)) 80 * 81 * where K is an n byte key 82 * ipad is the byte 0x36 repeated 64 times 83 * opad is the byte 0x5c repeated 64 times 84 * and text is the data being protected 85 */ 86 87 /* start out by storing key in pads */ 88 memset(k_ipad, 0, sizeof k_ipad); 89 memset(k_opad, 0, sizeof k_opad); 90 memcpy(k_ipad, key, key_len); 91 memcpy(k_opad, key, key_len); 92 93 /* XOR key with ipad and opad values */ 94 for (i=0; i<64; i++) { 95 k_ipad[i] ^= 0x36; 96 k_opad[i] ^= 0x5c; 97 } 98 99 /* 100 * perform inner MD5 101 */ 102 MD5_Init(&context); /* init context for 1st pass */ 103 MD5_Update(&context, k_ipad, 64); /* start with inner pad */ 104 MD5_Update(&context, text, text_len); /* then text of datagram */ 105 MD5_Final(digest, &context); /* finish up 1st pass */ 106 107 /* 108 * perform outer MD5 109 */ 110 MD5_Init(&context); /* init context for 2nd pass */ 111 MD5_Update(&context, k_opad, 64); /* start with outer pad */ 112 MD5_Update(&context, digest, 16); /* then results of 1st hash */ 113 MD5_Final(digest, &context); /* finish up 2nd pass */ 114 } 115 USES_APPLE_RST 116 #endif 117 118 #ifdef HAVE_LIBCRYPTO 119 /* 120 * Verify a cryptographic signature of the packet. 121 * Currently only MD5 is supported. 122 */ 123 int 124 signature_verify(netdissect_options *ndo, 125 const u_char *pptr, u_int plen, u_char *sig_ptr) 126 { 127 uint8_t rcvsig[16]; 128 uint8_t sig[16]; 129 unsigned int i; 130 131 /* 132 * Save the signature before clearing it. 133 */ 134 memcpy(rcvsig, sig_ptr, sizeof(rcvsig)); 135 memset(sig_ptr, 0, sizeof(rcvsig)); 136 137 if (!ndo->ndo_sigsecret) { 138 return (CANT_CHECK_SIGNATURE); 139 } 140 141 signature_compute_hmac_md5(pptr, plen, (unsigned char *)ndo->ndo_sigsecret, 142 strlen(ndo->ndo_sigsecret), sig); 143 144 if (memcmp(rcvsig, sig, sizeof(sig)) == 0) { 145 return (SIGNATURE_VALID); 146 147 } else { 148 149 for (i = 0; i < sizeof(sig); ++i) { 150 ND_PRINT((ndo, "%02x", sig[i])); 151 } 152 153 return (SIGNATURE_INVALID); 154 } 155 } 156 #endif 157 158 /* 159 * Local Variables: 160 * c-style: whitesmith 161 * c-basic-offset: 4 162 * End: 163 */ 164