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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);
+ }
+ }
+ }
+}