The Tcpdump Group git mirrors - tcpdump/blob - signature.c

   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  */