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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@gredler.at)
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "netdissect-stdinc.h"
#include <string.h>
#include <stdlib.h>
#include "netdissect.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_ALLOCATE_COPY, "can't allocate memory"},
{ CANT_CHECK_SIGNATURE, "unchecked"},
{ 0, NULL }
};
#ifdef HAVE_LIBCRYPTO
/*
* Compute a HMAC MD5 sum.
* Taken from rfc2104, Appendix.
*/
USES_APPLE_DEPRECATED_API
static void
signature_compute_hmac_md5(const uint8_t *text, int text_len, unsigned char *key,
unsigned int key_len, uint8_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 */
}
USES_APPLE_RST
/*
* Verify a cryptographic signature of the packet.
* Currently only MD5 is supported.
*/
int
signature_verify(netdissect_options *ndo, const u_char *pptr, u_int plen,
const u_char *sig_ptr, void (*clear_rtn)(void *),
const void *clear_arg)
{
uint8_t *packet_copy, *sig_copy;
uint8_t sig[16];
unsigned int i;
if (!ndo->ndo_sigsecret) {
return (CANT_CHECK_SIGNATURE);
}
/*
* Do we have all the packet data to be checked?
*/
if (!ND_TTEST_LEN(pptr, plen)) {
/* No. */
return (CANT_CHECK_SIGNATURE);
}
/*
* Do we have the entire signature to check?
*/
if (!ND_TTEST_LEN(sig_ptr, sizeof(sig))) {
/* No. */
return (CANT_CHECK_SIGNATURE);
}
if (sig_ptr + sizeof(sig) > pptr + plen) {
/* No. */
return (CANT_CHECK_SIGNATURE);
}
/*
* Make a copy of the packet, so we don't overwrite the original.
*/
packet_copy = malloc(plen);
if (packet_copy == NULL) {
return (CANT_ALLOCATE_COPY);
}
memcpy(packet_copy, pptr, plen);
/*
* Clear the signature in the copy.
*/
sig_copy = packet_copy + (sig_ptr - pptr);
memset(sig_copy, 0, sizeof(sig));
/*
* Clear anything else that needs to be cleared in the copy.
* Our caller is assumed to have vetted the clear_arg pointer.
*/
(*clear_rtn)((void *)(packet_copy + ((const uint8_t *)clear_arg - pptr)));
/*
* Compute the signature.
*/
signature_compute_hmac_md5(packet_copy, plen,
(unsigned char *)ndo->ndo_sigsecret,
strlen(ndo->ndo_sigsecret), sig);
/*
* Free the copy.
*/
free(packet_copy);
/*
* Does the computed signature match the signature in the packet?
*/
if (memcmp(sig_ptr, sig, sizeof(sig)) == 0) {
/* Yes. */
return (SIGNATURE_VALID);
} else {
/* No - print the computed signature. */
for (i = 0; i < sizeof(sig); ++i) {
ND_PRINT("%02x", sig[i]);
}
return (SIGNATURE_INVALID);
}
}
#else
int
signature_verify(netdissect_options *ndo _U_, const u_char *pptr _U_,
u_int plen _U_, const u_char *sig_ptr _U_,
void (*clear_rtn)(void *) _U_, const void *clear_arg _U_)
{
return (CANT_CHECK_SIGNATURE);
}
#endif
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