Subversion Repositories openrisc

/* MDGenerator.java --

   Copyright (C) 2001, 2002, 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.java.security.prng;

import gnu.java.security.Registry;

import gnu.java.security.hash.HashFactory;

import gnu.java.security.hash.IMessageDigest;

import java.util.Map;

/**

 * A simple pseudo-random number generator that relies on a hash algorithm, that

 * (a) starts its operation by hashing a <code>seed</code>, and then (b)

 * continuously re-hashing its output. If no hash algorithm name is specified in

 * the {@link Map} of attributes used to initialise the instance then the

 * SHA-160 algorithm is used as the underlying hash function. Also, if no

 * <code>seed</code> is given, an empty octet sequence is used.

 */

public class MDGenerator

    extends BasePRNG

    implements Cloneable

{

  /** Property name of underlying hash algorithm for this generator. */

  public static final String MD_NAME = "gnu.crypto.prng.md.hash.name";

  /** Property name of seed material. */

  public static final String SEEED = "gnu.crypto.prng.md.seed";

  /** The underlying hash instance. */

  private IMessageDigest md;

  /** Trivial 0-arguments constructor. */

  public MDGenerator()

  {

    super(Registry.MD_PRNG);

  }

  public void setup(Map attributes)

  {

    // find out which hash to use

    String underlyingMD = (String) attributes.get(MD_NAME);

    if (underlyingMD == null)

      {

        if (md == null)

          { // happy birthday

            // ensure we have a reliable implementation of this hash

            md = HashFactory.getInstance(Registry.SHA160_HASH);

          }

        else // a clone. reset it for reuse

          md.reset();

      }

    else // ensure we have a reliable implementation of this hash

      md = HashFactory.getInstance(underlyingMD);

    // get the seeed

    byte[] seed = (byte[]) attributes.get(SEEED);

    if (seed == null)

      seed = new byte[0];

    md.update(seed, 0, seed.length);

  }

  public void fillBlock() throws LimitReachedException

  {

    IMessageDigest mdc = (IMessageDigest) md.clone();

    buffer = mdc.digest();

    md.update(buffer, 0, buffer.length);

  }

  public void addRandomByte(final byte b)

  {

    if (md == null)

      throw new IllegalStateException("not initialized");

    md.update(b);

  }

  public void addRandomBytes(final byte[] buf, final int off, final int len)

  {

    if (md == null)

      throw new IllegalStateException("not initialized");

    md.update(buf, off, len);

  }

  public Object clone() throws CloneNotSupportedException

  {

    MDGenerator result = (MDGenerator) super.clone();

    if (this.md != null)

      result.md = (IMessageDigest) this.md.clone();

    return result;

  }

}