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1: /* CFB.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 feedback mode. CFB mode is a stream mode that operates on <i>s</i> 46: * bit blocks, where 1 <= <i>s</i> <= <i>b</i>, if <i>b</i> is the 47: * underlying cipher's block size. Encryption is: 48: * <pre> 49: * I[1] = IV 50: * I[j] = LSB(b-s, I[j-1]) | C[j-1] for j = 2...n 51: * O[j] = CIPH(K, I[j]) for j = 1,2...n 52: * C[j] = P[j] ˆ MSB(s, O[j]) for j = 1,2...n 53: * </pre> 54: * <p> 55: * And decryption is: 56: * <pre> 57: * I[1] = IV 58: * I[j] = LSB(b-s, I[j-1]) | C[j-1] for j = 2...n 59: * O[j] = CIPH(K, I[j]) for j = 1,2...n 60: * P[j] = C[j] ˆ MSB(s, O[j]) for j = 1,2...n 61: * </pre> 62: * <p> 63: * CFB mode requires an initialization vector, which need not be kept secret. 64: * <p> 65: * References: 66: * <ol> 67: * <li>Bruce Schneier, <i>Applied Cryptography: Protocols, Algorithms, and 68: * Source Code in C, Second Edition</i>. (1996 John Wiley and Sons) ISBN 69: * 0-471-11709-9.</li> 70: * <li><a 71: * href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf"> 72: * Recommendation for Block Cipher Modes of Operation Methods and Techniques</a>, 73: * Morris Dworkin.</li> 74: * </ol> 75: */ 76: public class CFB 77: extends BaseMode 78: { 79: /** The shift register, the input block to the block cipher. */ 80: private byte[] shiftRegister; 81: /** The output block from the block cipher. */ 82: private byte[] scratch; 83: 84: /** 85: * Package-private constructor for the factory class. 86: * 87: * @param underlyingCipher The cipher implementation. 88: * @param cipherBlockSize The cipher's block size. 89: */ 90: CFB(IBlockCipher underlyingCipher, int cipherBlockSize) 91: { 92: super(Registry.CFB_MODE, underlyingCipher, cipherBlockSize); 93: } 94: 95: /** 96: * Cloneing constructor. 97: * 98: * @param that The instance being cloned. 99: */ 100: private CFB(CFB that) 101: { 102: this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); 103: } 104: 105: public Object clone() 106: { 107: return new CFB(this); 108: } 109: 110: public void setup() 111: { 112: if (modeBlockSize > cipherBlockSize) 113: throw new IllegalArgumentException( 114: "CFB block size cannot be larger than the cipher block size"); 115: shiftRegister = new byte[cipherBlockSize]; 116: scratch = new byte[cipherBlockSize]; 117: System.arraycopy(iv, 0, 118: shiftRegister, 0, 119: Math.min(iv.length, cipherBlockSize)); 120: } 121: 122: public void teardown() 123: { 124: if (shiftRegister != null) 125: for (int i = 0; i < shiftRegister.length; i++) 126: shiftRegister[i] = 0; 127: shiftRegister = null; 128: } 129: 130: public void encryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) 131: { 132: cipher.encryptBlock(shiftRegister, 0, scratch, 0); 133: for (int i = 0; i < modeBlockSize; i++) 134: out[outOffset + i] = (byte)(in[inOffset + i] ^ scratch[i]); 135: System.arraycopy(shiftRegister, modeBlockSize, 136: shiftRegister, 0, 137: cipherBlockSize - modeBlockSize); 138: System.arraycopy(out, outOffset, 139: shiftRegister, cipherBlockSize - modeBlockSize, 140: modeBlockSize); 141: } 142: 143: public void decryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) 144: { 145: cipher.encryptBlock(shiftRegister, 0, scratch, 0); 146: for (int i = 0; i < modeBlockSize; i++) 147: out[outOffset + i] = (byte)(in[inOffset + i] ^ scratch[i]); 148: System.arraycopy(shiftRegister, modeBlockSize, 149: shiftRegister, 0, 150: cipherBlockSize - modeBlockSize); 151: System.arraycopy(in, inOffset, 152: shiftRegister, cipherBlockSize - modeBlockSize, 153: modeBlockSize); 154: } 155: }