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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* AFsplitter - Anti forensic information splitter
*
* Copyright (C) 2004 Clemens Fruhwirth <clemens@endorphin.org>
* Copyright (C) 2009-2025 Red Hat, Inc. All rights reserved.
*
* AFsplitter diffuses information over a large stripe of data,
* therefore supporting secure data destruction.
*/
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "internal.h"
#include "af.h"
static void XORblock(const char *src1, const char *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(const char *src, char *dst, uint32_t iv,
size_t len, const char *hash_name)
{
struct crypt_hash *hd = NULL;
char *iv_char = (char *)&iv;
int r;
iv = be32_to_cpu(iv);
if (crypt_hash_init(&hd, hash_name))
return -EINVAL;
if ((r = crypt_hash_write(hd, iv_char, sizeof(uint32_t))))
goto out;
if ((r = crypt_hash_write(hd, src, len)))
goto out;
r = crypt_hash_final(hd, dst, len);
out:
crypt_hash_destroy(hd);
return r;
}
/*
* diffuse: Information spreading over the whole dataset with
* the help of hash function.
*/
static int diffuse(char *src, char *dst, size_t size, const char *hash_name)
{
int r, hash_size = crypt_hash_size(hash_name);
unsigned int digest_size;
unsigned int i, blocks, padding;
if (hash_size <= 0)
return -EINVAL;
digest_size = hash_size;
blocks = size / digest_size;
padding = size % digest_size;
for (i = 0; i < blocks; i++) {
r = hash_buf(src + digest_size * i,
dst + digest_size * i,
i, (size_t)digest_size, hash_name);
if (r < 0)
return r;
}
if (padding) {
r = hash_buf(src + digest_size * i,
dst + digest_size * i,
i, (size_t)padding, hash_name);
if (r < 0)
return r;
}
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(struct crypt_device *ctx, const char *src, char *dst,
size_t blocksize, unsigned int blocknumbers, const char *hash)
{
unsigned int i;
char *bufblock;
int r;
bufblock = crypt_safe_alloc(blocksize);
if (!bufblock)
return -ENOMEM;
/* process everything except the last block */
for (i = 0; i < blocknumbers - 1; i++) {
r = crypt_random_get(ctx, dst + blocksize * i, blocksize, CRYPT_RND_NORMAL);
if (r < 0)
goto out;
XORblock(dst + blocksize * i, bufblock, bufblock, blocksize);
r = diffuse(bufblock, bufblock, blocksize, hash);
if (r < 0)
goto out;
}
/* the last block is computed */
XORblock(src, bufblock, dst + blocksize * i, blocksize);
r = 0;
out:
crypt_safe_free(bufblock);
return r;
}
int AF_merge(const char *src, char *dst,
size_t blocksize, unsigned int blocknumbers, const char *hash)
{
unsigned int i;
char *bufblock;
int r;
bufblock = crypt_safe_alloc(blocksize);
if (!bufblock)
return -ENOMEM;
for (i = 0; i < blocknumbers - 1; i++) {
XORblock(src + blocksize * i, bufblock, bufblock, blocksize);
r = diffuse(bufblock, bufblock, blocksize, hash);
if (r < 0)
goto out;
}
XORblock(src + blocksize * i, bufblock, dst, blocksize);
r = 0;
out:
crypt_safe_free(bufblock);
return r;
}
/* Size of final split data including sector alignment */
size_t AF_split_sectors(size_t blocksize, unsigned int blocknumbers)
{
size_t af_size;
/* data material * stripes */
af_size = blocksize * blocknumbers;
/* round up to sector */
af_size = (af_size + (SECTOR_SIZE - 1)) / SECTOR_SIZE;
return af_size;
}
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