1 /* CBC.java -- 2 Copyright (C) 2002, 2006 Free Software Foundation, Inc. 3 4 This file is a part of GNU Classpath. 5 6 GNU Classpath is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 2 of the License, or (at 9 your option) any later version. 10 11 GNU Classpath is distributed in the hope that it will be useful, but 12 WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GNU Classpath; if not, write to the Free Software 18 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 19 USA 20 21 Linking this library statically or dynamically with other modules is 22 making a combined work based on this library. Thus, the terms and 23 conditions of the GNU General Public License cover the whole 24 combination. 25 26 As a special exception, the copyright holders of this library give you 27 permission to link this library with independent modules to produce an 28 executable, regardless of the license terms of these independent 29 modules, and to copy and distribute the resulting executable under 30 terms of your choice, provided that you also meet, for each linked 31 independent module, the terms and conditions of the license of that 32 module. An independent module is a module which is not derived from 33 or based on this library. If you modify this library, you may extend 34 this exception to your version of the library, but you are not 35 obligated to do so. If you do not wish to do so, delete this 36 exception statement from your version. */ 37 38 39 package gnu.javax.crypto.mode; 40 41 import gnu.java.security.Registry; 42 import gnu.javax.crypto.cipher.IBlockCipher; 43 44 /** 45 * The Cipher Block Chaining mode. This mode introduces feedback into the cipher 46 * by XORing the previous ciphertext block with the plaintext block before 47 * encipherment. That is, encrypting looks like this: 48 * 49 * <pre> 50 * C<sub>i</sub> = E<sub>K</sub>(P<sub>i</sub>ˆ C<sub>i-1</sub>) 51 * </pre> 52 * <p> 53 * Similarly, decrypting is: 54 * <pre> 55 * P<sub>i</sub> = C<sub>i-1</sub> ˆ D<sub>K</sub>(C<sub>i</sub>) 56 * </pre> 57 */ 58 public class CBC 59 extends BaseMode 60 implements Cloneable 61 { 62 /** The last (de|en)crypted block */ 63 private byte[] lastBlock; 64 /** An intermediate buffer. */ 65 private byte[] scratch; 66 67 /** 68 * Package-private constructor for the factory class. 69 * 70 * @param underlyingCipher The cipher implementation. 71 * @param cipherBlockSize The cipher's block size. 72 */ CBC(IBlockCipher underlyingCipher, int cipherBlockSize)73 CBC(IBlockCipher underlyingCipher, int cipherBlockSize) 74 { 75 super(Registry.CBC_MODE, underlyingCipher, cipherBlockSize); 76 } 77 78 /** Our constructor for cloning. */ CBC(CBC that)79 private CBC(CBC that) 80 { 81 this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); 82 } 83 clone()84 public Object clone() 85 { 86 return new CBC(this); 87 } 88 setup()89 public void setup() 90 { 91 if (modeBlockSize != cipherBlockSize) 92 throw new IllegalArgumentException(); 93 scratch = new byte[cipherBlockSize]; 94 lastBlock = new byte[cipherBlockSize]; 95 // lastBlock gets initialized to the initialization vector. 96 for (int i = 0; i < lastBlock.length && i < iv.length; i++) 97 lastBlock[i] = iv[i]; 98 } 99 teardown()100 public void teardown() 101 { 102 lastBlock = null; 103 scratch = null; 104 } 105 encryptBlock(byte[] in, int i, byte[] out, int o)106 public void encryptBlock(byte[] in, int i, byte[] out, int o) 107 { 108 for (int k = 0; k < scratch.length; k++) 109 scratch[k] = (byte)(lastBlock[k] ^ in[k + i]); 110 cipher.encryptBlock(scratch, 0, out, o); 111 System.arraycopy(out, o, lastBlock, 0, cipherBlockSize); 112 } 113 decryptBlock(byte[] in, int i, byte[] out, int o)114 public void decryptBlock(byte[] in, int i, byte[] out, int o) 115 { 116 byte[] buf = new byte[cipherBlockSize]; 117 System.arraycopy(in, i, buf, 0, cipherBlockSize); 118 cipher.decryptBlock(in, i, scratch, 0); 119 for (int k = 0; k < scratch.length; k++) 120 out[o + k] = (byte)(lastBlock[k] ^ scratch[k]); 121 System.arraycopy(buf, 0, lastBlock, 0, cipherBlockSize); 122 } 123 } 124