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+/* KDF.java --
+ Copyright (C) 2003, 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.javax.crypto.sasl.srp;
+
+import gnu.java.security.Registry;
+import gnu.java.security.prng.LimitReachedException;
+import gnu.java.security.util.PRNG;
+import gnu.javax.crypto.cipher.IBlockCipher;
+import gnu.javax.crypto.prng.UMacGenerator;
+
+import java.util.HashMap;
+
+/**
+ * The SASL-SRP KDF implementation, which is also used, depending on how it was
+ * instantiated, as a secure Pseudo Random Number Generator.
+ */
+public class KDF
+{
+ private static final int AES_BLOCK_SIZE = 16; // default block size for AES
+ private static final int AES_KEY_SIZE = 16; // default key size for the AES
+ private static final byte[] buffer = new byte[1];
+ /** Our default source of randomness. */
+ private static final PRNG prng = PRNG.getInstance();
+ /** The underlying UMAC Generator instance. */
+ private UMacGenerator umac = null;
+
+ /**
+ * Constructs an instance of the <code>KDF</code> initialised with the
+ * designated shared secret bytes.
+ *
+ * @param keyMaterial the SASL SRP shared secret (K) bytes.
+ */
+ private KDF(final byte[] keyMaterial, final int ndx)
+ {
+ super();
+
+ final HashMap map = new HashMap();
+ map.put(UMacGenerator.CIPHER, Registry.AES_CIPHER);
+ map.put(UMacGenerator.INDEX, Integer.valueOf(ndx));
+ map.put(IBlockCipher.CIPHER_BLOCK_SIZE, Integer.valueOf(AES_BLOCK_SIZE));
+ final byte[] key = new byte[AES_KEY_SIZE];
+ System.arraycopy(keyMaterial, 0, key, 0, AES_KEY_SIZE);
+ map.put(IBlockCipher.KEY_MATERIAL, key);
+ umac = new UMacGenerator();
+ umac.init(map);
+ }
+
+ /**
+ * A Factory mehod that returns an instance of a <code>KDF</code> based on
+ * supplied seed data.
+ *
+ * @param K the SASL SRP shared secret for a <code>KDF</code> to be used for
+ * <i>CALG</i> and <i>IALG</i> setup. <code>null</code> otherwise.
+ * @return an instance of a <code>KDF</code>.
+ */
+ static final KDF getInstance(final byte[] K)
+ {
+ int ndx = -1;
+ final byte[] keyMaterial;
+ if (K != null)
+ {
+ keyMaterial = K;
+ ndx = 0;
+ }
+ else
+ {
+ keyMaterial = new byte[AES_BLOCK_SIZE];
+ while (ndx < 1 || ndx > 255)
+ ndx = (byte) nextByte();
+ }
+ return new KDF(keyMaterial, ndx);
+ }
+
+ private static synchronized final int nextByte()
+ {
+ prng.nextBytes(buffer);
+ return (buffer[0] & 0xFF);
+ }
+
+ /**
+ * Returns a designated number of bytes suitable for use in the SASL SRP
+ * mechanism.
+ *
+ * @param length the number of bytes needed.
+ * @return a byte array containing the generated/selected bytes.
+ */
+ public synchronized byte[] derive(final int length)
+ {
+ final byte[] result = new byte[length];
+ try
+ {
+ umac.nextBytes(result, 0, length);
+ }
+ catch (IllegalStateException x) // should not happen
+ {
+ x.printStackTrace(System.err);
+ }
+ catch (LimitReachedException x) // idem
+ {
+ x.printStackTrace(System.err);
+ }
+ return result;
+ }
+}