| /* 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. |
| * <p> |
| * 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 <tt>1</tt>, then <tt>0</tt> bits are appended, and if the trailing |
| * bit is <tt>0</tt>, then <tt>1</tt> bits are appended. As few bits are |
| * added as are necessary to meet the formatting size requirement." |
| * <p> |
| * References: |
| * <ol> |
| * <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 final class TBC |
| extends BasePad |
| { |
| private static final Logger log = Logger.getLogger(TBC.class.getName()); |
| |
| /** |
| * Trivial package-private constructor for use by the <i>Factory</i> 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; |
| } |
| } |