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/* CBC.java --

   Copyright (C) 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath 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.

GNU Classpath 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

General Public License for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; if not, write to the Free Software

Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301

USA

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version.  */

package gnu.javax.crypto.mode;

import gnu.java.security.Registry;

import gnu.javax.crypto.cipher.IBlockCipher;

/**

 * The Cipher Block Chaining mode. This mode introduces feedback into the cipher

 * by XORing the previous ciphertext block with the plaintext block before

 * encipherment. That is, encrypting looks like this:

 *

 * <pre>

 *  C<sub>i</sub> = E<sub>K</sub>(P<sub>i</sub>&circ; C<sub>i-1</sub>)

 * </pre>

 * <p>

 * Similarly, decrypting is:

 * <pre>

 *  P<sub>i</sub> = C<sub>i-1</sub> &circ; D<sub>K</sub>(C<sub>i</sub>)

 * </pre>

 */

public class CBC

    extends BaseMode

    implements Cloneable

{

  /** The last (de|en)crypted block */

  private byte[] lastBlock;

  /** An intermediate buffer. */

  private byte[] scratch;

  /**

   * Package-private constructor for the factory class.

   *

   * @param underlyingCipher The cipher implementation.

   * @param cipherBlockSize The cipher's block size.

   */

  CBC(IBlockCipher underlyingCipher, int cipherBlockSize)

  {

    super(Registry.CBC_MODE, underlyingCipher, cipherBlockSize);

  }

  /** Our constructor for cloning. */

  private CBC(CBC that)

  {

    this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize);

  }

  public Object clone()

  {

    return new CBC(this);

  }

  public void setup()

  {

    if (modeBlockSize != cipherBlockSize)

      throw new IllegalArgumentException();

    scratch = new byte[cipherBlockSize];

    lastBlock = new byte[cipherBlockSize];

    // lastBlock gets initialized to the initialization vector.

    for (int i = 0; i < lastBlock.length && i < iv.length; i++)

      lastBlock[i] = iv[i];

  }

  public void teardown()

  {

    lastBlock = null;

    scratch = null;

  }

  public void encryptBlock(byte[] in, int i, byte[] out, int o)

  {

    for (int k = 0; k < scratch.length; k++)

      scratch[k] = (byte)(lastBlock[k] ^ in[k + i]);

    cipher.encryptBlock(scratch, 0, out, o);

    System.arraycopy(out, o, lastBlock, 0, cipherBlockSize);

  }

  public void decryptBlock(byte[] in, int i, byte[] out, int o)

  {

    byte[] buf = new byte[cipherBlockSize];

    System.arraycopy(in, i, buf, 0, cipherBlockSize);

    cipher.decryptBlock(in, i, scratch, 0);

    for (int k = 0; k < scratch.length; k++)

      out[o + k] = (byte)(lastBlock[k] ^ scratch[k]);

    System.arraycopy(buf, 0, lastBlock, 0, cipherBlockSize);

  }

}