package gnu.crypto.prng;
// ----------------------------------------------------------------------------
// $Id: MDGenerator.java,v 1.10 2005/10/06 04:24:17 rsdio Exp $
//
// Copyright (C) 2001, 2002, 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
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// library, you may extend this exception to your version of the
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// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------
import gnu.crypto.Registry;
import gnu.crypto.hash.HashFactory;
import gnu.crypto.hash.IMessageDigest;
import java.util.Map;
/**
* <p>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.</p>
*
* @version $Revision: 1.10 $
*/
public class MDGenerator extends BasePRNG implements Cloneable {
// Constants and variables
// -------------------------------------------------------------------------
/** 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;
// Constructor(s)
// -------------------------------------------------------------------------
/** Trivial 0-arguments constructor. */
public MDGenerator() {
super(Registry.MD_PRNG);
}
// Class methods
// -------------------------------------------------------------------------
// Instance methods
// -------------------------------------------------------------------------
// Implementation of abstract methods in BaseRandom ------------------------
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);
}
}