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