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/*
* AFsplitter - Anti forensic information splitter
* Copyright 2004, Clemens Fruhwirth <clemens@endorphin.org>
* Copyright (C) 2009 Red Hat, Inc. All rights reserved.
*
* AFsplitter diffuses information over a large stripe of data,
* therefor supporting secure data destruction.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Library General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <errno.h>
#include <gcrypt.h>
#include "random.h"
static void XORblock(char const *src1, char const *src2, char *dst, size_t n)
{
size_t j;
for(j = 0; j < n; ++j)
dst[j] = src1[j] ^ src2[j];
}
static int hash_buf(char *src, char *dst, uint32_t iv, int len, int hash_id)
{
gcry_md_hd_t hd;
unsigned char *digest;
iv = htonl(iv);
if (gcry_md_open(&hd, hash_id, 0))
return 1;
gcry_md_write(hd, (unsigned char *)&iv, sizeof(iv));
gcry_md_write(hd, src, len);
digest = gcry_md_read(hd, hash_id);
memcpy(dst, digest, len);
gcry_md_close(hd);
return 0;
}
/* diffuse: Information spreading over the whole dataset with
* the help of hash function.
*/
static int diffuse(char *src, char *dst, size_t size, int hash_id)
{
unsigned int digest_size = gcry_md_get_algo_dlen(hash_id);
unsigned int i, blocks, padding;
blocks = size / digest_size;
padding = size % digest_size;
for (i = 0; i < blocks; i++)
if(hash_buf(src + digest_size * i,
dst + digest_size * i,
i, digest_size, hash_id))
return 1;
if(padding)
if(hash_buf(src + digest_size * i,
dst + digest_size * i,
i, padding, hash_id))
return 1;
return 0;
}
/*
* Information splitting. The amount of data is multiplied by
* blocknumbers. The same blocksize and blocknumbers values
* must be supplied to AF_merge to recover information.
*/
int AF_split(char *src, char *dst, size_t blocksize, unsigned int blocknumbers, const char *hash)
{
unsigned int i;
char *bufblock;
int r = -EINVAL;
int hash_id;
if (!(hash_id = gcry_md_map_name(hash)))
return -EINVAL;
if((bufblock = calloc(blocksize, 1)) == NULL) return -ENOMEM;
/* process everything except the last block */
for(i=0; i<blocknumbers-1; i++) {
r = getRandom(dst+(blocksize*i),blocksize);
if(r < 0) goto out;
XORblock(dst+(blocksize*i),bufblock,bufblock,blocksize);
if(diffuse(bufblock, bufblock, blocksize, hash_id))
goto out;
}
/* the last block is computed */
XORblock(src,bufblock,dst+(i*blocksize),blocksize);
r = 0;
out:
free(bufblock);
return r;
}
int AF_merge(char *src, char *dst, size_t blocksize, unsigned int blocknumbers, const char *hash)
{
unsigned int i;
char *bufblock;
int r = -EINVAL;
int hash_id;
if (!(hash_id = gcry_md_map_name(hash)))
return -EINVAL;
if((bufblock = calloc(blocksize, 1)) == NULL) return -ENOMEM;
memset(bufblock,0,blocksize);
for(i=0; i<blocknumbers-1; i++) {
XORblock(src+(blocksize*i),bufblock,bufblock,blocksize);
if(diffuse(bufblock, bufblock, blocksize, hash_id))
goto out;
}
XORblock(src + blocksize * i, bufblock, dst, blocksize);
r = 0;
out:
free(bufblock);
return 0;
}
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