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/* PRNG.java -- A Utility methods for default source of randomness

   Copyright (C) 2006 Free Software Foundation, Inc.

This file is 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, 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; 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. */

package gnu.java.security.util;

import java.util.HashMap;

import gnu.java.security.prng.IRandom;

import gnu.java.security.prng.LimitReachedException;

import gnu.java.security.prng.MDGenerator;

/**

 * A useful hash-based (SHA) pseudo-random number generator used throughout this

 * library.

 *

 * @see MDGenerator

 */

public class PRNG

{

  /** The underlying {@link IRandom}. */

  private IRandom delegate;

  /**

   * Private constructor to enforce using the Factory method.

   *

   * @param delegate the undelying {@link IRandom} object used.

   */

  private PRNG(IRandom delegate)

  {

    super();

    this.delegate = delegate;

  }

  public static final PRNG getInstance()

  {

    IRandom delegate = new MDGenerator();

    try

      {

        HashMap map = new HashMap();

        // initialise it with a seed

        long t = System.currentTimeMillis();

        byte[] seed = new byte[] {

            (byte)(t >>> 56), (byte)(t >>> 48),

            (byte)(t >>> 40), (byte)(t >>> 32),

            (byte)(t >>> 24), (byte)(t >>> 16),

            (byte)(t >>>  8), (byte) t };

        map.put(MDGenerator.SEEED, seed);

        delegate.init(map); // default is to use SHA-1 hash

      }

    catch (Exception x)

      {

        throw new ExceptionInInitializerError(x);

      }

    return new PRNG(delegate);

  }

  /**

   * Completely fills the designated <code>buffer</code> with random data

   * generated by the underlying delegate.

   *

   * @param buffer the place holder of random bytes generated by the underlying

   *          delegate. On output, the contents of <code>buffer</code> are

   *          replaced with pseudo-random data, iff the <code>buffer</code>

   *          size is not zero.

   */

  public void nextBytes(byte[] buffer)

  {

    nextBytes(buffer, 0, buffer.length);

  }

  /**

   * Fills the designated <code>buffer</code>, starting from byte at position

   * <code>offset</code> with, at most, <code>length</code> bytes of random

   * data generated by the underlying delegate.

   *

   * @see IRandom#nextBytes

   */

  public void nextBytes(byte[] buffer, int offset, int length)

  {

    try

      {

        delegate.nextBytes(buffer, offset, length);

      }

    catch (LimitReachedException x) // re-initialise with a seed

      {

        try

          {

            HashMap map = new HashMap();

            long t = System.currentTimeMillis();

            byte[] seed = new byte[] {

                (byte)(t >>> 56), (byte)(t >>> 48),

                (byte)(t >>> 40), (byte)(t >>> 32),

                (byte)(t >>> 24), (byte)(t >>> 16),

                (byte)(t >>>  8), (byte) t };

            map.put(MDGenerator.SEEED, seed);

            delegate.init(map); // default is to use SHA-1 hash

            delegate.nextBytes(buffer, offset, length);

          }

        catch (Exception y)

          {

            throw new ExceptionInInitializerError(y);

          }

      }

  }

}