lib/luks1/af.c

   1 /*
   2  * AFsplitter - Anti forensic information splitter
   3  *
   4  * Copyright (C) 2004, Clemens Fruhwirth <clemens@endorphin.org>
   5  * Copyright (C) 2009-2011, Red Hat, Inc. All rights reserved.
   6  *
   7  * AFsplitter diffuses information over a large stripe of data,
   8  * therefor supporting secure data destruction.
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License
  12  * version 2 as published by the Free Software Foundation.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU Library General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  22  */
  23
  24 #include <stddef.h>
  25 #include <stdlib.h>
  26 #include <string.h>
  27 #include <netinet/in.h>
  28 #include <errno.h>
  29 #include "crypto_backend.h"
  30 #include "internal.h"
  31 #include "af.h"
  32
  33 static void XORblock(const char *src1, const char *src2, char *dst, size_t n)
  34 {
  35         size_t j;
  36
  37         for(j = 0; j < n; ++j)
  38                 dst[j] = src1[j] ^ src2[j];
  39 }
  40
  41 static int hash_buf(const char *src, char *dst, uint32_t iv,
  42                     size_t len, const char *hash_name)
  43 {
  44         struct crypt_hash *hd = NULL;
  45         char *iv_char = (char *)&iv;
  46         int r;
  47
  48         iv = htonl(iv);
  49         if (crypt_hash_init(&hd, hash_name))
  50                 return -EINVAL;
  51
  52         if ((r = crypt_hash_write(hd, iv_char, sizeof(uint32_t))))
  53                 goto out;
  54
  55         if ((r = crypt_hash_write(hd, src, len)))
  56                 goto out;
  57
  58         r = crypt_hash_final(hd, dst, len);
  59 out:
  60         crypt_hash_destroy(hd);
  61         return r;
  62 }
  63
  64 /* diffuse: Information spreading over the whole dataset with
  65  * the help of hash function.
  66  */
  67
  68 static int diffuse(char *src, char *dst, size_t size, const char *hash_name)
  69 {
  70         unsigned int digest_size = crypt_hash_size(hash_name);
  71         unsigned int i, blocks, padding;
  72
  73         blocks = size / digest_size;
  74         padding = size % digest_size;
  75
  76         for (i = 0; i < blocks; i++)
  77                 if(hash_buf(src + digest_size * i,
  78                             dst + digest_size * i,
  79                             i, (size_t)digest_size, hash_name))
  80                         return 1;
  81
  82         if(padding)
  83                 if(hash_buf(src + digest_size * i,
  84                             dst + digest_size * i,
  85                             i, (size_t)padding, hash_name))
  86                         return 1;
  87
  88         return 0;
  89 }
  90
  91 /*
  92  * Information splitting. The amount of data is multiplied by
  93  * blocknumbers. The same blocksize and blocknumbers values
  94  * must be supplied to AF_merge to recover information.
  95  */
  96
  97 int AF_split(char *src, char *dst, size_t blocksize,
  98              unsigned int blocknumbers, const char *hash)
  99 {
 100         unsigned int i;
 101         char *bufblock;
 102         int r = -EINVAL;
 103
 104         if((bufblock = calloc(blocksize, 1)) == NULL) return -ENOMEM;
 105
 106         /* process everything except the last block */
 107         for(i=0; i<blocknumbers-1; i++) {
 108                 r = crypt_random_get(NULL, dst+(blocksize*i), blocksize, CRYPT_RND_NORMAL);
 109                 if(r < 0) goto out;
 110
 111                 XORblock(dst+(blocksize*i),bufblock,bufblock,blocksize);
 112                 if(diffuse(bufblock, bufblock, blocksize, hash))
 113                         goto out;
 114         }
 115         /* the last block is computed */
 116         XORblock(src,bufblock,dst+(i*blocksize),blocksize);
 117         r = 0;
 118 out:
 119         free(bufblock);
 120         return r;
 121 }
 122
 123 int AF_merge(char *src, char *dst, size_t blocksize,
 124              unsigned int blocknumbers, const char *hash)
 125 {
 126         unsigned int i;
 127         char *bufblock;
 128         int r = -EINVAL;
 129
 130         if((bufblock = calloc(blocksize, 1)) == NULL)
 131                 return -ENOMEM;
 132
 133         memset(bufblock,0,blocksize);
 134         for(i=0; i<blocknumbers-1; i++) {
 135                 XORblock(src+(blocksize*i),bufblock,bufblock,blocksize);
 136                 if(diffuse(bufblock, bufblock, blocksize, hash))
 137                         goto out;
 138         }
 139         XORblock(src + blocksize * i, bufblock, dst, blocksize);
 140         r = 0;
 141 out:
 142         free(bufblock);
 143         return r;
 144 }