1214456Srpaulo/* 2214456Srpaulo * Redistribution and use in source and binary forms, with or without 3214456Srpaulo * modification, are permitted provided that: (1) source code 4214456Srpaulo * distributions retain the above copyright notice and this paragraph 5214456Srpaulo * in its entirety, and (2) distributions including binary code include 6214456Srpaulo * the above copyright notice and this paragraph in its entirety in 7214456Srpaulo * the documentation or other materials provided with the distribution. 8214456Srpaulo * THIS SOFTWARE IS PROVIDED ``AS IS'' AND 9214456Srpaulo * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT 10214456Srpaulo * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 11214456Srpaulo * FOR A PARTICULAR PURPOSE. 12214456Srpaulo * 13214456Srpaulo * Functions for signature and digest verification. 14214456Srpaulo * 15214456Srpaulo * Original code by Hannes Gredler (hannes@juniper.net) 16214456Srpaulo */ 17214456Srpaulo 18214456Srpaulo#ifndef lint 19214456Srpaulostatic const char rcsid[] _U_ = 20214456Srpaulo "@(#) $Header: /tcpdump/master/tcpdump/signature.c,v 1.2 2008-09-22 20:22:10 guy Exp $ (LBL)"; 21214456Srpaulo#endif 22214456Srpaulo 23214456Srpaulo#ifdef HAVE_CONFIG_H 24214456Srpaulo#include "config.h" 25214456Srpaulo#endif 26214456Srpaulo 27214456Srpaulo#include <tcpdump-stdinc.h> 28214456Srpaulo 29214456Srpaulo#include <string.h> 30214456Srpaulo 31214456Srpaulo#include "interface.h" 32214456Srpaulo#include "signature.h" 33214456Srpaulo 34214456Srpaulo#ifdef HAVE_LIBCRYPTO 35214456Srpaulo#include <openssl/md5.h> 36214456Srpaulo#endif 37214456Srpaulo 38214456Srpauloconst struct tok signature_check_values[] = { 39214456Srpaulo { SIGNATURE_VALID, "valid"}, 40214456Srpaulo { SIGNATURE_INVALID, "invalid"}, 41214456Srpaulo { CANT_CHECK_SIGNATURE, "unchecked"}, 42214456Srpaulo { 0, NULL } 43214456Srpaulo}; 44214456Srpaulo 45214456Srpaulo 46214456Srpaulo#ifdef HAVE_LIBCRYPTO 47214456Srpaulo/* 48214456Srpaulo * Compute a HMAC MD5 sum. 49214456Srpaulo * Taken from rfc2104, Appendix. 50214456Srpaulo */ 51214456Srpaulostatic void 52214456Srpaulosignature_compute_hmac_md5(const u_int8_t *text, int text_len, unsigned char *key, 53214456Srpaulo unsigned int key_len, u_int8_t *digest) 54214456Srpaulo{ 55214456Srpaulo MD5_CTX context; 56214456Srpaulo unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */ 57214456Srpaulo unsigned char k_opad[65]; /* outer padding - key XORd with opad */ 58214456Srpaulo unsigned char tk[16]; 59214456Srpaulo int i; 60214456Srpaulo 61214456Srpaulo /* if key is longer than 64 bytes reset it to key=MD5(key) */ 62214456Srpaulo if (key_len > 64) { 63214456Srpaulo 64214456Srpaulo MD5_CTX tctx; 65214456Srpaulo 66214456Srpaulo MD5_Init(&tctx); 67214456Srpaulo MD5_Update(&tctx, key, key_len); 68214456Srpaulo MD5_Final(tk, &tctx); 69214456Srpaulo 70214456Srpaulo key = tk; 71214456Srpaulo key_len = 16; 72214456Srpaulo } 73214456Srpaulo 74214456Srpaulo /* 75214456Srpaulo * the HMAC_MD5 transform looks like: 76214456Srpaulo * 77214456Srpaulo * MD5(K XOR opad, MD5(K XOR ipad, text)) 78214456Srpaulo * 79214456Srpaulo * where K is an n byte key 80214456Srpaulo * ipad is the byte 0x36 repeated 64 times 81214456Srpaulo * opad is the byte 0x5c repeated 64 times 82214456Srpaulo * and text is the data being protected 83214456Srpaulo */ 84214456Srpaulo 85214456Srpaulo /* start out by storing key in pads */ 86214456Srpaulo memset(k_ipad, 0, sizeof k_ipad); 87214456Srpaulo memset(k_opad, 0, sizeof k_opad); 88214456Srpaulo memcpy(k_ipad, key, key_len); 89214456Srpaulo memcpy(k_opad, key, key_len); 90214456Srpaulo 91214456Srpaulo /* XOR key with ipad and opad values */ 92214456Srpaulo for (i=0; i<64; i++) { 93214456Srpaulo k_ipad[i] ^= 0x36; 94214456Srpaulo k_opad[i] ^= 0x5c; 95214456Srpaulo } 96214456Srpaulo 97214456Srpaulo /* 98214456Srpaulo * perform inner MD5 99214456Srpaulo */ 100214456Srpaulo MD5_Init(&context); /* init context for 1st pass */ 101214456Srpaulo MD5_Update(&context, k_ipad, 64); /* start with inner pad */ 102214456Srpaulo MD5_Update(&context, text, text_len); /* then text of datagram */ 103214456Srpaulo MD5_Final(digest, &context); /* finish up 1st pass */ 104214456Srpaulo 105214456Srpaulo /* 106214456Srpaulo * perform outer MD5 107214456Srpaulo */ 108214456Srpaulo MD5_Init(&context); /* init context for 2nd pass */ 109214456Srpaulo MD5_Update(&context, k_opad, 64); /* start with outer pad */ 110214456Srpaulo MD5_Update(&context, digest, 16); /* then results of 1st hash */ 111214456Srpaulo MD5_Final(digest, &context); /* finish up 2nd pass */ 112214456Srpaulo} 113214456Srpaulo#endif 114214456Srpaulo 115214456Srpaulo#ifdef HAVE_LIBCRYPTO 116214456Srpaulo/* 117214456Srpaulo * Verify a cryptographic signature of the packet. 118214456Srpaulo * Currently only MD5 is supported. 119214456Srpaulo */ 120214456Srpauloint 121214456Srpaulosignature_verify (const u_char *pptr, u_int plen, u_char *sig_ptr) 122214456Srpaulo{ 123214456Srpaulo u_int8_t rcvsig[16]; 124214456Srpaulo u_int8_t sig[16]; 125214456Srpaulo unsigned int i; 126214456Srpaulo 127214456Srpaulo /* 128214456Srpaulo * Save the signature before clearing it. 129214456Srpaulo */ 130214456Srpaulo memcpy(rcvsig, sig_ptr, sizeof(rcvsig)); 131214456Srpaulo memset(sig_ptr, 0, sizeof(rcvsig)); 132214456Srpaulo 133214456Srpaulo if (!sigsecret) { 134214456Srpaulo return (CANT_CHECK_SIGNATURE); 135214456Srpaulo } 136214456Srpaulo 137214456Srpaulo signature_compute_hmac_md5(pptr, plen, (unsigned char *)sigsecret, 138214456Srpaulo strlen(sigsecret), sig); 139214456Srpaulo 140214456Srpaulo if (memcmp(rcvsig, sig, sizeof(sig)) == 0) { 141214456Srpaulo return (SIGNATURE_VALID); 142214456Srpaulo 143214456Srpaulo } else { 144214456Srpaulo 145214456Srpaulo for (i = 0; i < sizeof(sig); ++i) { 146214456Srpaulo (void)printf("%02x", sig[i]); 147214456Srpaulo } 148214456Srpaulo 149214456Srpaulo return (SIGNATURE_INVALID); 150214456Srpaulo } 151214456Srpaulo} 152214456Srpaulo#endif 153214456Srpaulo 154214456Srpaulo/* 155214456Srpaulo * Local Variables: 156214456Srpaulo * c-style: whitesmith 157214456Srpaulo * c-basic-offset: 4 158214456Srpaulo * End: 159214456Srpaulo */ 160