| /* CFB.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 feedback mode. CFB mode is a stream mode that operates on <i>s</i> |
| * bit blocks, where 1 <= <i>s</i> <= <i>b</i>, if <i>b</i> is the |
| * underlying cipher's block size. Encryption is: |
| * <pre> |
| * I[1] = IV |
| * I[j] = LSB(b-s, I[j-1]) | C[j-1] for j = 2...n |
| * O[j] = CIPH(K, I[j]) for j = 1,2...n |
| * C[j] = P[j] ˆ MSB(s, O[j]) for j = 1,2...n |
| * </pre> |
| * <p> |
| * And decryption is: |
| * <pre> |
| * I[1] = IV |
| * I[j] = LSB(b-s, I[j-1]) | C[j-1] for j = 2...n |
| * O[j] = CIPH(K, I[j]) for j = 1,2...n |
| * P[j] = C[j] ˆ MSB(s, O[j]) for j = 1,2...n |
| * </pre> |
| * <p> |
| * CFB mode requires an initialization vector, which need not be kept secret. |
| * <p> |
| * References: |
| * <ol> |
| * <li>Bruce Schneier, <i>Applied Cryptography: Protocols, Algorithms, and |
| * Source Code in C, Second Edition</i>. (1996 John Wiley and Sons) ISBN |
| * 0-471-11709-9.</li> |
| * <li><a |
| * href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf"> |
| * Recommendation for Block Cipher Modes of Operation Methods and Techniques</a>, |
| * Morris Dworkin.</li> |
| * </ol> |
| */ |
| public class CFB |
| extends BaseMode |
| { |
| /** The shift register, the input block to the block cipher. */ |
| private byte[] shiftRegister; |
| /** The output block from the block cipher. */ |
| private byte[] scratch; |
| |
| /** |
| * Package-private constructor for the factory class. |
| * |
| * @param underlyingCipher The cipher implementation. |
| * @param cipherBlockSize The cipher's block size. |
| */ |
| CFB(IBlockCipher underlyingCipher, int cipherBlockSize) |
| { |
| super(Registry.CFB_MODE, underlyingCipher, cipherBlockSize); |
| } |
| |
| /** |
| * Cloneing constructor. |
| * |
| * @param that The instance being cloned. |
| */ |
| private CFB(CFB that) |
| { |
| this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); |
| } |
| |
| public Object clone() |
| { |
| return new CFB(this); |
| } |
| |
| public void setup() |
| { |
| if (modeBlockSize > cipherBlockSize) |
| throw new IllegalArgumentException( |
| "CFB block size cannot be larger than the cipher block size"); |
| shiftRegister = new byte[cipherBlockSize]; |
| scratch = new byte[cipherBlockSize]; |
| System.arraycopy(iv, 0, |
| shiftRegister, 0, |
| Math.min(iv.length, cipherBlockSize)); |
| } |
| |
| public void teardown() |
| { |
| if (shiftRegister != null) |
| for (int i = 0; i < shiftRegister.length; i++) |
| shiftRegister[i] = 0; |
| shiftRegister = null; |
| } |
| |
| public void encryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) |
| { |
| cipher.encryptBlock(shiftRegister, 0, scratch, 0); |
| for (int i = 0; i < modeBlockSize; i++) |
| out[outOffset + i] = (byte)(in[inOffset + i] ^ scratch[i]); |
| System.arraycopy(shiftRegister, modeBlockSize, |
| shiftRegister, 0, |
| cipherBlockSize - modeBlockSize); |
| System.arraycopy(out, outOffset, |
| shiftRegister, cipherBlockSize - modeBlockSize, |
| modeBlockSize); |
| } |
| |
| public void decryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) |
| { |
| cipher.encryptBlock(shiftRegister, 0, scratch, 0); |
| for (int i = 0; i < modeBlockSize; i++) |
| out[outOffset + i] = (byte)(in[inOffset + i] ^ scratch[i]); |
| System.arraycopy(shiftRegister, modeBlockSize, |
| shiftRegister, 0, |
| cipherBlockSize - modeBlockSize); |
| System.arraycopy(in, inOffset, |
| shiftRegister, cipherBlockSize - modeBlockSize, |
| modeBlockSize); |
| } |
| } |