/* cipher-ofb.c  - Generic OFB mode implementation

 * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003

 *               2005, 2007, 2008, 2009, 2011 Free Software Foundation, Inc.

 *

 * This file is part of Libgcrypt.

 *

 * Libgcrypt is free software; you can redistribute it and/or modify

 * it under the terms of the GNU Lesser general Public License as

 * published by the Free Software Foundation; either version 2.1 of

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

 *

 * Libgcrypt 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 Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with this program; if not, see <http://www.gnu.org/licenses/>.

 */

#include <config.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include "g10lib.h"

#include "cipher.h"

#include "bufhelp.h"

#include "./cipher-internal.h"

gcry_err_code_t

_gcry_cipher_ofb_encrypt (gcry_cipher_hd_t c,

                          unsigned char *outbuf, size_t outbuflen,

                          const unsigned char *inbuf, size_t inbuflen)

{

  unsigned char *ivp;

  gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;

  size_t blocksize_shift = _gcry_blocksize_shift(c);

  size_t blocksize = 1 << blocksize_shift;

  unsigned int burn, nburn;

  if (outbuflen < inbuflen)

    return GPG_ERR_BUFFER_TOO_SHORT;

  if ( inbuflen <= c->unused )

    {

      /* Short enough to be encoded by the remaining XOR mask. */

      /* XOR the input with the IV */

      ivp = c->u_iv.iv + blocksize - c->unused;

      buf_xor(outbuf, ivp, inbuf, inbuflen);

      c->unused -= inbuflen;

      return 0;

    }

  burn = 0;

  if( c->unused )

    {

      inbuflen -= c->unused;

      ivp = c->u_iv.iv + blocksize - c->unused;

      buf_xor(outbuf, ivp, inbuf, c->unused);

      outbuf += c->unused;

      inbuf += c->unused;

      c->unused = 0;

    }

  /* Now we can process complete blocks. */

  if (c->bulk.ofb_enc)

    {

      size_t nblocks = inbuflen >> blocksize_shift;

      c->bulk.ofb_enc (&c->context.c, c->u_iv.iv, outbuf, inbuf, nblocks);

      outbuf += nblocks << blocksize_shift;

      inbuf  += nblocks << blocksize_shift;

      inbuflen -= nblocks << blocksize_shift;

    }

  else

    {

      while ( inbuflen >= blocksize )

  {

    /* Encrypt the IV (and save the current one). */

    nburn = enc_fn ( &c->context.c, c->u_iv.iv, c->u_iv.iv );

    burn = nburn > burn ? nburn : burn;

    cipher_block_xor(outbuf, c->u_iv.iv, inbuf, blocksize);

    outbuf += blocksize;

    inbuf += blocksize;

    inbuflen -= blocksize;

  }

    }

  if ( inbuflen )

    { /* process the remaining bytes */

      nburn = enc_fn ( &c->context.c, c->u_iv.iv, c->u_iv.iv );

      burn = nburn > burn ? nburn : burn;

      c->unused = blocksize;

      c->unused -= inbuflen;

      buf_xor(outbuf, c->u_iv.iv, inbuf, inbuflen);

      outbuf += inbuflen;

      inbuf += inbuflen;

      inbuflen = 0;

    }

  if (burn > 0)

    _gcry_burn_stack (burn + 4 * sizeof(void *));

  return 0;

}