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BasePad.java

package gnu.crypto.pad;

// ----------------------------------------------------------------------------
// $Id: BasePad.java,v 1.6 2005/10/06 04:24:17 rsdio Exp $
//
// Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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, or (at your option)
// any later version.
//
// GNU Crypto 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 this program; see the file COPYING.  If not, write to the
//
//    Free Software Foundation Inc.,
//    51 Franklin Street, 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.
// ----------------------------------------------------------------------------

/**
 * <p>An abstract class to facilitate implementing padding algorithms.</p>
 *
 * @version $Revision: 1.6 $
 */
00051 public abstract class BasePad implements IPad {

   // Constants and variables
   // -------------------------------------------------------------------------

   /** The canonical name prefix of the padding algorithm. */
00057    protected String name;

   /** The block size, in bytes, for this instance. */
00060    protected int blockSize;

   // Constructor(s)
   // -------------------------------------------------------------------------

   /** Trivial constructor for use by concrete subclasses. */
00066    protected BasePad(final String name) {
      super();

      this.name = name;
      blockSize = -1;
   }

   // Class methods
   // -------------------------------------------------------------------------

   // Instance methods
   // -------------------------------------------------------------------------

   // IPad interface implementation -------------------------------------------

00081    public String name() {
      final StringBuffer sb = new StringBuffer(name);
      if (blockSize != -1) {
         sb.append('-').append(String.valueOf(8*blockSize));
      }
      return sb.toString();
   }

   public void init(final int bs) throws IllegalStateException {
      if (blockSize != -1) {
         throw new IllegalStateException();
      }
      blockSize = bs;
      setup();
   }

00097    public void reset() {
      blockSize = -1;
   }

00101    public boolean selfTest() {
      byte[] padBytes;
      final int offset = 5;
      final int limit = 1024;
      final byte[] in = new byte[limit];
      for (int bs = 2; bs < 256; bs++) {
         this.init(bs);
         for (int i = 0; i < limit-offset-blockSize; i++) {
            padBytes = pad(in, offset, i);
            if (((i + padBytes.length) % blockSize) != 0) {
               new RuntimeException(name()).printStackTrace(System.err);
               return false;
            }

            System.arraycopy(padBytes, 0, in, offset+i, padBytes.length);
            try {
               if (padBytes.length != unpad(in, offset, i+padBytes.length)) {
                  new RuntimeException(name()).printStackTrace(System.err);
                  return false;
               }
            } catch (WrongPaddingException x) {
               x.printStackTrace(System.err);
               return false;
            }
         }
         this.reset();
      }

      return true;
   }

   // abstract methods to implement by subclasses -----------------------------

   /**
    * <p>If any additional checks or resource setup must be done by the
    * subclass, then this is the hook for it. This method will be called before
    * the {@link #init(int)} method returns.</p>
    */
   public abstract void setup();

   public abstract byte[] pad(byte[] in, int off, int len);

   public abstract int unpad(byte[] in, int off, int len)
   throws WrongPaddingException;
}

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