Line data    Source code

       1             : /* cipher-ofb.c  - Generic OFB mode implementation
       2             :  * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003
       3             :  *               2005, 2007, 2008, 2009, 2011 Free Software Foundation, Inc.
       4             :  *
       5             :  * This file is part of Libgcrypt.
       6             :  *
       7             :  * Libgcrypt is free software; you can redistribute it and/or modify
       8             :  * it under the terms of the GNU Lesser general Public License as
       9             :  * published by the Free Software Foundation; either version 2.1 of
      10             :  * the License, or (at your option) any later version.
      11             :  *
      12             :  * Libgcrypt is distributed in the hope that it will be useful,
      13             :  * but WITHOUT ANY WARRANTY; without even the implied warranty of
      14             :  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      15             :  * GNU Lesser General Public License for more details.
      16             :  *
      17             :  * You should have received a copy of the GNU Lesser General Public
      18             :  * License along with this program; if not, see <http://www.gnu.org/licenses/>.
      19             :  */
      20             : 
      21             : #include <config.h>
      22             : #include <stdio.h>
      23             : #include <stdlib.h>
      24             : #include <string.h>
      25             : #include <errno.h>
      26             : 
      27             : #include "g10lib.h"
      28             : #include "cipher.h"
      29             : #include "bufhelp.h"
      30             : #include "./cipher-internal.h"
      31             : 
      32             : 
      33             : gcry_err_code_t
      34           0 : _gcry_cipher_ofb_encrypt (gcry_cipher_hd_t c,
      35             :                           unsigned char *outbuf, size_t outbuflen,
      36             :                           const unsigned char *inbuf, size_t inbuflen)
      37             : {
      38             :   unsigned char *ivp;
      39           0 :   gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
      40           0 :   size_t blocksize = c->spec->blocksize;
      41             :   unsigned int burn, nburn;
      42             : 
      43           0 :   if (outbuflen < inbuflen)
      44           0 :     return GPG_ERR_BUFFER_TOO_SHORT;
      45             : 
      46           0 :   if ( inbuflen <= c->unused )
      47             :     {
      48             :       /* Short enough to be encoded by the remaining XOR mask. */
      49             :       /* XOR the input with the IV */
      50           0 :       ivp = c->u_iv.iv + blocksize - c->unused;
      51           0 :       buf_xor(outbuf, ivp, inbuf, inbuflen);
      52           0 :       c->unused -= inbuflen;
      53           0 :       return 0;
      54             :     }
      55             : 
      56           0 :   burn = 0;
      57             : 
      58           0 :   if( c->unused )
      59             :     {
      60           0 :       inbuflen -= c->unused;
      61           0 :       ivp = c->u_iv.iv + blocksize - c->unused;
      62           0 :       buf_xor(outbuf, ivp, inbuf, c->unused);
      63           0 :       outbuf += c->unused;
      64           0 :       inbuf += c->unused;
      65           0 :       c->unused = 0;
      66             :     }
      67             : 
      68             :   /* Now we can process complete blocks. */
      69           0 :   while ( inbuflen >= blocksize )
      70             :     {
      71             :       /* Encrypt the IV (and save the current one). */
      72           0 :       nburn = enc_fn ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
      73           0 :       burn = nburn > burn ? nburn : burn;
      74           0 :       buf_xor(outbuf, c->u_iv.iv, inbuf, blocksize);
      75           0 :       outbuf += blocksize;
      76           0 :       inbuf += blocksize;
      77           0 :       inbuflen -= blocksize;
      78             :     }
      79           0 :   if ( inbuflen )
      80             :     { /* process the remaining bytes */
      81           0 :       nburn = enc_fn ( &c->context.c, c->u_iv.iv, c->u_iv.iv );
      82           0 :       burn = nburn > burn ? nburn : burn;
      83           0 :       c->unused = blocksize;
      84           0 :       c->unused -= inbuflen;
      85           0 :       buf_xor(outbuf, c->u_iv.iv, inbuf, inbuflen);
      86           0 :       outbuf += inbuflen;
      87           0 :       inbuf += inbuflen;
      88           0 :       inbuflen = 0;
      89             :     }
      90             : 
      91           0 :   if (burn > 0)
      92           0 :     _gcry_burn_stack (burn + 4 * sizeof(void *));
      93             : 
      94           0 :   return 0;
      95             : }