/* TBC.java -- Copyright (C) 2001, 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.pad; import gnu.java.security.Configuration; import gnu.java.security.Registry; import gnu.java.security.util.Util; import java.util.logging.Logger; /** * The implementation of the Trailing Bit Complement (TBC) padding algorithm. *

* In this mode, "...the data string is padded at the trailing end with the * complement of the trailing bit of the unpadded message: if the trailing bit * is 1, then 0 bits are appended, and if the trailing * bit is 0, then 1 bits are appended. As few bits are * added as are necessary to meet the formatting size requirement." *

* References: *

    *
  1. * Recommendation for Block Cipher Modes of Operation Methods and * Techniques, Morris Dworkin.
  2. *
*/ public final class TBC extends BasePad { private static final Logger log = Logger.getLogger(TBC.class.getName()); /** * Trivial package-private constructor for use by the Factory class. * * @see PadFactory */ TBC() { super(Registry.TBC_PAD); } public void setup() { if (blockSize < 1 || blockSize > 256) throw new IllegalArgumentException(); } public byte[] pad(byte[] in, int offset, int length) { int padLength = blockSize; if (length % blockSize != 0) padLength = blockSize - length % blockSize; byte[] result = new byte[padLength]; int lastBit = in[offset + length - 1] & 0x01; if (lastBit == 0) for (int i = 0; i < padLength;) result[i++] = 0x01; // else it's already set to zeroes by virtue of initialisation if (Configuration.DEBUG) log.fine("padding: 0x" + Util.toString(result)); return result; } public int unpad(byte[] in, int offset, int length) throws WrongPaddingException { int limit = offset + length - 1; int lastBit = in[limit] & 0xFF; int result = 0; while (lastBit == (in[limit] & 0xFF)) { result++; limit--; } if (result > length) throw new WrongPaddingException(); if (Configuration.DEBUG) log.fine("padding length: " + result); return result; } }