package gnu.crypto.sasl.srp;

// ----------------------------------------------------------------------------
// $Id: KDF.java,v 1.4 2005/10/06 04:24:18 rsdio Exp $
//
// Copyright (C) 2003 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
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// do so, delete this exception statement from your version.
// ----------------------------------------------------------------------------

import gnu.crypto.Registry;
import gnu.crypto.cipher.IBlockCipher;
import gnu.crypto.prng.LimitReachedException;
import gnu.crypto.prng.UMacGenerator;
import gnu.crypto.util.PRNG;

import java.util.HashMap;

/**
 * <p>The SASL-SRP KDF implementation, which is also used, depending on how it
 * was instantiated, as a secure Pseudo Random Number Generator.</p>
 *
 * @version $Revision: 1.4 $
 */
public class KDF {

   // Constants and variables
   // -------------------------------------------------------------------------

   private static final int AES_BLOCK_SIZE = 16; // default block size for the AES
   private static final int AES_KEY_SIZE = 16; // default key size for the AES
   private static final byte[] buffer = new byte[1];

   /** The shared secret K to use. */
//   private byte[] keyMaterial;

   /** The underlying UMAC Generator instance. */
   private UMacGenerator umac = null;

   // Constructor(s)
   // -------------------------------------------------------------------------

   /**
    * <p>Constructs an instance of the <code>KDF</code> initialised with the
    * designated shared secret bytes.</p>
    *
    * @param keyMaterial the SASL SRP shared secret (K) bytes.
    */
   private KDF(final byte[] keyMaterial, final int ndx) {
      super();

//      if (ndx != 0) {
//         this.keyMaterial = (byte[]) keyMaterial.clone();
//      }
      final HashMap map = new HashMap();
      map.put(UMacGenerator.CIPHER, Registry.AES_CIPHER);
      map.put(UMacGenerator.INDEX, new Integer(ndx));
      map.put(IBlockCipher.CIPHER_BLOCK_SIZE, new Integer(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);
//System.out.println("**** Initialised KDF with: "+gnu.crypto.util.Util.dumpString(key));
   }

   // Class methods
   // -------------------------------------------------------------------------

   /**
    * <p>A Factory mehod that returns an instance of a <code>KDF</code> based on
    * supplied seed data.</p>
    *
    * @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);
   }

   // Instance methods
   // -------------------------------------------------------------------------

   /**
    * <p>Returns a designated number of bytes suitable for use in the SASL SRP
    * mechanism.</p>
    *
    * @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];
//      if (keyMaterial == null || length > keyMaterial.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);
      }
//      } else {
//         System.arraycopy(keyMaterial, 0, result, 0, length);
//      }

      return result;
   }
}
