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package gnu.crypto.mode;
// ----------------------------------------------------------------------------
// $Id: CBC.java,v 1.2 2004/01/07 23:05:49 rsdio Exp $
//
// Copyright (C) 2002 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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, or (at your option)
// any later version.
//
// GNU Crypto 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 this program; see the file COPYING. If not, write to the
//
// Free Software Foundation Inc.,
// 59 Temple Place - Suite 330,
// Boston, MA 02111-1307
// 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.
// ----------------------------------------------------------------------------
import gnu.crypto.Registry;
import gnu.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:
*
* Ci = EK(Pi ^
* Ci-1
*
* Similarly, decrypting is:
*
* Pi = Ci-1 ^
* DK(Ci)
*
* @version $Revision: 1.2 $
*/
public class CBC extends BaseMode implements Cloneable {
// Constants and Variables
//------------------------------------------------------------------
/** The last (de|en)crypted block */
private byte[] lastBlock;
/** An intermediate buffer. */
private byte[] scratch;
// Constructors
// -----------------------------------------------------------------
/**
* 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);
}
// Cloneable interface implementation
// -----------------------------------------------------------------
public Object clone() {
return new CBC(this);
}
// Implementation of abstract methods in BaseMode
// -----------------------------------------------------------------
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);
}
}