Source for gnu.javax.crypto.pad.TBC

   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: }