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1: /* TBC.java -- 2: Copyright (C) 2001, 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.pad; 40: 41: import gnu.java.security.Configuration; 42: import gnu.java.security.Registry; 43: import gnu.java.security.util.Util; 44: 45: import java.util.logging.Logger; 46: 47: /** 48: * The implementation of the Trailing Bit Complement (TBC) padding algorithm. 49: * <p> 50: * In this mode, "...the data string is padded at the trailing end with the 51: * complement of the trailing bit of the unpadded message: if the trailing bit 52: * is <tt>1</tt>, then <tt>0</tt> bits are appended, and if the trailing 53: * bit is <tt>0</tt>, then <tt>1</tt> bits are appended. As few bits are 54: * added as are necessary to meet the formatting size requirement." 55: * <p> 56: * References: 57: * <ol> 58: * <li><a 59: * href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf"> 60: * Recommendation for Block Cipher Modes of Operation Methods and 61: * Techniques</a>, Morris Dworkin.</li> 62: * </ol> 63: */ 64: public final class TBC 65: extends BasePad 66: { 67: private static final Logger log = Logger.getLogger(TBC.class.getName()); 68: 69: /** 70: * Trivial package-private constructor for use by the <i>Factory</i> class. 71: * 72: * @see PadFactory 73: */ 74: TBC() 75: { 76: super(Registry.TBC_PAD); 77: } 78: 79: public void setup() 80: { 81: if (blockSize < 1 || blockSize > 256) 82: throw new IllegalArgumentException(); 83: } 84: 85: public byte[] pad(byte[] in, int offset, int length) 86: { 87: int padLength = blockSize; 88: if (length % blockSize != 0) 89: padLength = blockSize - length % blockSize; 90: byte[] result = new byte[padLength]; 91: int lastBit = in[offset + length - 1] & 0x01; 92: if (lastBit == 0) 93: for (int i = 0; i < padLength;) 94: result[i++] = 0x01; 95: // else it's already set to zeroes by virtue of initialisation 96: if (Configuration.DEBUG) 97: log.fine("padding: 0x" + Util.toString(result)); 98: return result; 99: } 100: 101: public int unpad(byte[] in, int offset, int length) 102: throws WrongPaddingException 103: { 104: int limit = offset + length - 1; 105: int lastBit = in[limit] & 0xFF; 106: int result = 0; 107: while (lastBit == (in[limit] & 0xFF)) 108: { 109: result++; 110: limit--; 111: } 112: if (result > length) 113: throw new WrongPaddingException(); 114: if (Configuration.DEBUG) 115: log.fine("padding length: " + result); 116: return result; 117: } 118: }