/* cipher-cfb.c  - Generic CFB 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_cfb_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;

  size_t blocksize_x_2 = blocksize + blocksize;

  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 and store input into IV. */

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

      buf_xor_2dst(outbuf, ivp, inbuf, inbuflen);

      c->unused -= inbuflen;

      return 0;

    }

  burn = 0;

  if ( c->unused )

    {

      /* XOR the input with the IV and store input into IV */

      inbuflen -= c->unused;

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

      buf_xor_2dst(outbuf, ivp, inbuf, c->unused);

      outbuf += c->unused;

      inbuf += c->unused;

      c->unused = 0;

    }

  /* Now we can process complete blocks.  We use a loop as long as we

     have at least 2 blocks and use conditions for the rest.  This

     also allows to use a bulk encryption function if available.  */

  if (inbuflen >= blocksize_x_2 && c->bulk.cfb_enc)

    {

      size_t nblocks = inbuflen >> blocksize_shift;

      c->bulk.cfb_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_x_2 )

        {

          /* Encrypt the IV. */

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

          burn = nburn > burn ? nburn : burn;

          /* XOR the input with the IV and store input into IV.  */

          cipher_block_xor_2dst(outbuf, c->u_iv.iv, inbuf, blocksize);

          outbuf += blocksize;

          inbuf += blocksize;

          inbuflen -= blocksize;

        }

    }

  if ( inbuflen >= blocksize )

    {

      /* Save the current IV and then encrypt the IV. */

      cipher_block_cpy( c->lastiv, c->u_iv.iv, blocksize );

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

      burn = nburn > burn ? nburn : burn;

      /* XOR the input with the IV and store input into IV */

      cipher_block_xor_2dst(outbuf, c->u_iv.iv, inbuf, blocksize);

      outbuf += blocksize;

      inbuf += blocksize;

      inbuflen -= blocksize;

    }

  if ( inbuflen )

    {

      /* Save the current IV and then encrypt the IV. */

      cipher_block_cpy( c->lastiv, c->u_iv.iv, blocksize );

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

      burn = nburn > burn ? nburn : burn;

      c->unused = blocksize;

      /* Apply the XOR. */

      c->unused -= inbuflen;

      buf_xor_2dst(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;

}

gcry_err_code_t

_gcry_cipher_cfb_decrypt (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;

  size_t blocksize_x_2 = blocksize + blocksize;

  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 and store input into IV. */

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

      buf_xor_n_copy(outbuf, ivp, inbuf, inbuflen);

      c->unused -= inbuflen;

      return 0;

    }

  burn = 0;

  if (c->unused)

    {

      /* XOR the input with the IV and store input into IV. */

      inbuflen -= c->unused;

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

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

      outbuf += c->unused;

      inbuf += c->unused;

      c->unused = 0;

    }

  /* Now we can process complete blocks.  We use a loop as long as we

     have at least 2 blocks and use conditions for the rest.  This

     also allows to use a bulk encryption function if available.  */

  if (inbuflen >= blocksize_x_2 && c->bulk.cfb_dec)

    {

      size_t nblocks = inbuflen >> blocksize_shift;

      c->bulk.cfb_dec (&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_x_2 )

        {

          /* Encrypt the IV. */

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

          burn = nburn > burn ? nburn : burn;

          /* XOR the input with the IV and store input into IV. */

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

          outbuf += blocksize;

          inbuf += blocksize;

          inbuflen -= blocksize;

        }

    }

  if (inbuflen >= blocksize )

    {

      /* Save the current IV and then encrypt the IV. */

      cipher_block_cpy ( c->lastiv, c->u_iv.iv, blocksize);

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

      burn = nburn > burn ? nburn : burn;

      /* XOR the input with the IV and store input into IV */

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

      outbuf += blocksize;

      inbuf += blocksize;

      inbuflen -= blocksize;

    }

  if (inbuflen)

    {

      /* Save the current IV and then encrypt the IV. */

      cipher_block_cpy ( c->lastiv, c->u_iv.iv, blocksize );

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

      burn = nburn > burn ? nburn : burn;

      c->unused = blocksize;

      /* Apply the XOR. */

      c->unused -= inbuflen;

      buf_xor_n_copy(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;

}

gcry_err_code_t

_gcry_cipher_cfb8_encrypt (gcry_cipher_hd_t c,

                          unsigned char *outbuf, size_t outbuflen,

                          const unsigned char *inbuf, size_t inbuflen)

{

  gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;

  size_t blocksize = c->spec->blocksize;

  unsigned int burn, nburn;

  if (outbuflen < inbuflen)

    return GPG_ERR_BUFFER_TOO_SHORT;

  burn = 0;

  while ( inbuflen > 0)

    {

      int i;

      /* Encrypt the IV. */

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

      burn = nburn > burn ? nburn : burn;

      outbuf[0] = c->lastiv[0] ^ inbuf[0];

      /* Bitshift iv by 8 bit to the left */

      for (i = 0; i < blocksize-1; i++)

        c->u_iv.iv[i] = c->u_iv.iv[i+1];

      /* append cipher text to iv */

      c->u_iv.iv[blocksize-1] = outbuf[0];

      outbuf += 1;

      inbuf += 1;

      inbuflen -= 1;

    }

  if (burn > 0)

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

  return 0;

}

gcry_err_code_t

_gcry_cipher_cfb8_decrypt (gcry_cipher_hd_t c,

                          unsigned char *outbuf, size_t outbuflen,

                          const unsigned char *inbuf, size_t inbuflen)

{

  gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;

  size_t blocksize = c->spec->blocksize;

  unsigned int burn, nburn;

  unsigned char appendee;

  if (outbuflen < inbuflen)

    return GPG_ERR_BUFFER_TOO_SHORT;

  burn = 0;

  while (inbuflen > 0)

    {

      int i;

      /* Encrypt the IV. */

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

      burn = nburn > burn ? nburn : burn;

      /* inbuf might == outbuf, make sure we keep the value

         so we can append it later */

      appendee = inbuf[0];

      outbuf[0] = inbuf[0] ^ c->lastiv[0];

      /* Bitshift iv by 8 bit to the left */

      for (i = 0; i < blocksize-1; i++)

        c->u_iv.iv[i] = c->u_iv.iv[i+1];

      c->u_iv.iv[blocksize-1] = appendee;

      outbuf += 1;

      inbuf += 1;

      inbuflen -= 1;

    }

  if (burn > 0)

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

  return 0;

}