/*

 * AFsplitter - Anti forensic information splitter

 *

 * Copyright (C) 2004 Clemens Fruhwirth <clemens@endorphin.org>

 * Copyright (C) 2009-2024 Red Hat, Inc. All rights reserved.

 *

 * AFsplitter diffuses information over a large stripe of data,

 * therefore 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

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 *

 * 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

 */

#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;

}