Source for gnu.javax.crypto.pad.ISO10126

   1: /* ISO10126.java -- An implementation of the ISO 10126-2 padding scheme
   2:    Copyright (C) 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.Registry;
  42: import gnu.java.security.util.PRNG;
  43: 
  44: /**
  45:  * The implementation of the ISO 10126-2 padding algorithm.
  46:  * <p>
  47:  * The last byte of the padding block is the number of padding bytes, all other
  48:  * padding bytes are random.
  49:  * <p>
  50:  * References:
  51:  * <ol>
  52:  *    <li><a href="http://www.w3.org/TR/xmlenc-core/">XML Encryption Syntax and
  53:  *    Processing</a> Section "5.2 Block Encryption Algorithms"; "Padding".</li>
  54:  * </ol>
  55:  */
  56: public final class ISO10126
  57:     extends BasePad
  58: {
  59:   /** Used to generate random numbers for padding bytes. */
  60:   private PRNG prng;
  61: 
  62:   ISO10126()
  63:   {
  64:     super(Registry.ISO10126_PAD);
  65:     prng = PRNG.getInstance();
  66:   }
  67: 
  68:   public void setup()
  69:   {
  70:     // Nothing to do here
  71:   }
  72: 
  73:   public byte[] pad(byte[] in, int offset, int length)
  74:   {
  75:     int padLength = blockSize - (length % blockSize);
  76:     final byte[] pad = new byte[padLength];
  77: 
  78:     // generate random numbers for the padding bytes except for the last byte
  79:     prng.nextBytes(pad, 0, padLength - 1);
  80:     // the last byte contains the number of padding bytes
  81:     pad[padLength - 1] = (byte) padLength;
  82: 
  83:     return pad;
  84:   }
  85: 
  86:   public int unpad(byte[] in, int offset, int length)
  87:       throws WrongPaddingException
  88:   {
  89:     // the last byte contains the number of padding bytes
  90:     int padLength = in[offset + length - 1] & 0xFF;
  91:     if (padLength > length)
  92:       throw new WrongPaddingException();
  93: 
  94:     return padLength;
  95:   }
  96: 
  97:   /**
  98:    * The default self-test in the super-class would take too long to finish
  99:    * with this type of padder --due to the large amount of random data needed.
 100:    * We override the default test and replace it with a simple one for a 16-byte
 101:    * block-size (default AES block-size). The Mauve test TestOfISO10126 will
 102:    * exercise all block-sizes that the default self-test uses for the other
 103:    * padders.
 104:    */
 105:   public boolean selfTest()
 106:   {
 107:     return test1BlockSize(16, new byte[1024]);
 108:   }
 109: }