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+/* 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;
+ }
+}