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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libjava/] [classpath/] [gnu/] [java/] [security/] [prng/] [MDGenerator.java] - Blame information for rev 769

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1 769 jeremybenn
/* MDGenerator.java --
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   Copyright (C) 2001, 2002, 2006  Free Software Foundation, Inc.
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This file is a part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library.  Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module.  An independent module is a module which is not derived from
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or based on this library.  If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so.  If you do not wish to do so, delete this
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exception statement from your version.  */
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package gnu.java.security.prng;
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import gnu.java.security.Registry;
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import gnu.java.security.hash.HashFactory;
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import gnu.java.security.hash.IMessageDigest;
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import java.util.Map;
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/**
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 * A simple pseudo-random number generator that relies on a hash algorithm, that
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 * (a) starts its operation by hashing a <code>seed</code>, and then (b)
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 * continuously re-hashing its output. If no hash algorithm name is specified in
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 * the {@link Map} of attributes used to initialise the instance then the
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 * SHA-160 algorithm is used as the underlying hash function. Also, if no
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 * <code>seed</code> is given, an empty octet sequence is used.
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 */
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public class MDGenerator
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    extends BasePRNG
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    implements Cloneable
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{
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  /** Property name of underlying hash algorithm for this generator. */
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  public static final String MD_NAME = "gnu.crypto.prng.md.hash.name";
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  /** Property name of seed material. */
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  public static final String SEEED = "gnu.crypto.prng.md.seed";
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  /** The underlying hash instance. */
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  private IMessageDigest md;
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  /** Trivial 0-arguments constructor. */
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  public MDGenerator()
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  {
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    super(Registry.MD_PRNG);
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  }
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  public void setup(Map attributes)
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  {
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    // find out which hash to use
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    String underlyingMD = (String) attributes.get(MD_NAME);
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    if (underlyingMD == null)
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      {
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        if (md == null)
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          { // happy birthday
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            // ensure we have a reliable implementation of this hash
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            md = HashFactory.getInstance(Registry.SHA160_HASH);
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          }
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        else // a clone. reset it for reuse
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          md.reset();
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      }
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    else // ensure we have a reliable implementation of this hash
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      md = HashFactory.getInstance(underlyingMD);
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    // get the seeed
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    byte[] seed = (byte[]) attributes.get(SEEED);
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    if (seed == null)
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      seed = new byte[0];
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    md.update(seed, 0, seed.length);
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  }
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  public void fillBlock() throws LimitReachedException
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  {
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    IMessageDigest mdc = (IMessageDigest) md.clone();
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    buffer = mdc.digest();
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    md.update(buffer, 0, buffer.length);
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  }
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  public void addRandomByte(final byte b)
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  {
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    if (md == null)
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      throw new IllegalStateException("not initialized");
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    md.update(b);
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  }
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  public void addRandomBytes(final byte[] buf, final int off, final int len)
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  {
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    if (md == null)
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      throw new IllegalStateException("not initialized");
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    md.update(buf, off, len);
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  }
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  public Object clone() throws CloneNotSupportedException
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  {
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    MDGenerator result = (MDGenerator) super.clone();
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    if (this.md != null)
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      result.md = (IMessageDigest) this.md.clone();
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    return result;
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  }
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}

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