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/* ISO10126.java -- An implementation of the ISO 10126-2 padding scheme

   Copyright (C) 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.Registry;

import gnu.java.security.util.PRNG;

/**

 * The implementation of the ISO 10126-2 padding algorithm.

 * <p>

 * The last byte of the padding block is the number of padding bytes, all other

 * padding bytes are random.

 * <p>

 * References:

 * <ol>

 *    <li><a href="http://www.w3.org/TR/xmlenc-core/">XML Encryption Syntax and

 *    Processing</a> Section "5.2 Block Encryption Algorithms"; "Padding".</li>

 * </ol>

 */

public final class ISO10126

    extends BasePad

{

  /** Used to generate random numbers for padding bytes. */

  private PRNG prng;

  ISO10126()

  {

    super(Registry.ISO10126_PAD);

    prng = PRNG.getInstance();

  }

  public void setup()

  {

    // Nothing to do here

  }

  public byte[] pad(byte[] in, int offset, int length)

  {

    int padLength = blockSize - (length % blockSize);

    final byte[] pad = new byte[padLength];

    // generate random numbers for the padding bytes except for the last byte

    prng.nextBytes(pad, 0, padLength - 1);

    // the last byte contains the number of padding bytes

    pad[padLength - 1] = (byte) padLength;

    return pad;

  }

  public int unpad(byte[] in, int offset, int length)

      throws WrongPaddingException

  {

    // the last byte contains the number of padding bytes

    int padLength = in[offset + length - 1] & 0xFF;

    if (padLength > length)

      throw new WrongPaddingException();

    return padLength;

  }

  /**

   * The default self-test in the super-class would take too long to finish

   * with this type of padder --due to the large amount of random data needed.

   * We override the default test and replace it with a simple one for a 16-byte

   * block-size (default AES block-size). The Mauve test TestOfISO10126 will

   * exercise all block-sizes that the default self-test uses for the other

   * padders.

   */

  public boolean selfTest()

  {

    return test1BlockSize(16, new byte[1024]);

  }

}