160 lines
4.1 KiB
C
160 lines
4.1 KiB
C
/*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that: (1) source code
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* distributions retain the above copyright notice and this paragraph
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* in its entirety, and (2) distributions including binary code include
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* the above copyright notice and this paragraph in its entirety in
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* the documentation or other materials provided with the distribution.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND
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* WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
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* LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE.
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*
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* Functions for signature and digest verification.
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*
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* Original code by Hannes Gredler (hannes@juniper.net)
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*/
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#ifndef lint
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static const char rcsid[] _U_ =
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"@(#) $Header: /tcpdump/master/tcpdump/signature.c,v 1.2 2008-09-22 20:22:10 guy Exp $ (LBL)";
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#endif
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <tcpdump-stdinc.h>
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#include <string.h>
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#include "interface.h"
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#include "signature.h"
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#ifdef HAVE_LIBCRYPTO
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#include <openssl/md5.h>
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#endif
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const struct tok signature_check_values[] = {
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{ SIGNATURE_VALID, "valid"},
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{ SIGNATURE_INVALID, "invalid"},
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{ CANT_CHECK_SIGNATURE, "unchecked"},
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{ 0, NULL }
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};
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#ifdef HAVE_LIBCRYPTO
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/*
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* Compute a HMAC MD5 sum.
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* Taken from rfc2104, Appendix.
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*/
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static void
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signature_compute_hmac_md5(const u_int8_t *text, int text_len, unsigned char *key,
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unsigned int key_len, u_int8_t *digest)
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{
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MD5_CTX context;
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unsigned char k_ipad[65]; /* inner padding - key XORd with ipad */
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unsigned char k_opad[65]; /* outer padding - key XORd with opad */
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unsigned char tk[16];
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int i;
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/* if key is longer than 64 bytes reset it to key=MD5(key) */
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if (key_len > 64) {
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MD5_CTX tctx;
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MD5_Init(&tctx);
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MD5_Update(&tctx, key, key_len);
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MD5_Final(tk, &tctx);
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key = tk;
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key_len = 16;
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}
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/*
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* the HMAC_MD5 transform looks like:
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*
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* MD5(K XOR opad, MD5(K XOR ipad, text))
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*
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* where K is an n byte key
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* ipad is the byte 0x36 repeated 64 times
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* opad is the byte 0x5c repeated 64 times
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* and text is the data being protected
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*/
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/* start out by storing key in pads */
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memset(k_ipad, 0, sizeof k_ipad);
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memset(k_opad, 0, sizeof k_opad);
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memcpy(k_ipad, key, key_len);
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memcpy(k_opad, key, key_len);
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/* XOR key with ipad and opad values */
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for (i=0; i<64; i++) {
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k_ipad[i] ^= 0x36;
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k_opad[i] ^= 0x5c;
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}
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/*
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* perform inner MD5
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*/
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MD5_Init(&context); /* init context for 1st pass */
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MD5_Update(&context, k_ipad, 64); /* start with inner pad */
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MD5_Update(&context, text, text_len); /* then text of datagram */
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MD5_Final(digest, &context); /* finish up 1st pass */
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/*
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* perform outer MD5
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*/
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MD5_Init(&context); /* init context for 2nd pass */
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MD5_Update(&context, k_opad, 64); /* start with outer pad */
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MD5_Update(&context, digest, 16); /* then results of 1st hash */
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MD5_Final(digest, &context); /* finish up 2nd pass */
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}
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#endif
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#ifdef HAVE_LIBCRYPTO
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/*
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* Verify a cryptographic signature of the packet.
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* Currently only MD5 is supported.
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*/
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int
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signature_verify (const u_char *pptr, u_int plen, u_char *sig_ptr)
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{
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u_int8_t rcvsig[16];
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u_int8_t sig[16];
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unsigned int i;
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/*
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* Save the signature before clearing it.
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*/
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memcpy(rcvsig, sig_ptr, sizeof(rcvsig));
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memset(sig_ptr, 0, sizeof(rcvsig));
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if (!sigsecret) {
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return (CANT_CHECK_SIGNATURE);
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}
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signature_compute_hmac_md5(pptr, plen, (unsigned char *)sigsecret,
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strlen(sigsecret), sig);
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if (memcmp(rcvsig, sig, sizeof(sig)) == 0) {
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return (SIGNATURE_VALID);
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} else {
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for (i = 0; i < sizeof(sig); ++i) {
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(void)printf("%02x", sig[i]);
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}
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return (SIGNATURE_INVALID);
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}
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}
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#endif
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/*
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* Local Variables:
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* c-style: whitesmith
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* c-basic-offset: 4
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* End:
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*/
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