| /* 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>ˆ C<sub>i-1</sub>) |
| * </pre> |
| * <p> |
| * Similarly, decrypting is: |
| * <pre> |
| * P<sub>i</sub> = C<sub>i-1</sub> ˆ 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); |
| } |
| } |