package gnu.crypto.key;

// ----------------------------------------------------------------------------
// $Id: BaseKeyAgreementParty.java,v 1.3 2005/10/06 04:24:16 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
// 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.
// ----------------------------------------------------------------------------

import gnu.crypto.prng.IRandom;
import gnu.crypto.prng.LimitReachedException;
import gnu.crypto.util.PRNG;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Map;

/**
 * <p>A base abstract class to facilitate implementations of concrete key
 * agreement protocol handlers.</p>
 *
 * @version $Revision: 1.3 $
 */
public abstract class BaseKeyAgreementParty implements IKeyAgreementParty {

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

   protected static final BigInteger TWO = BigInteger.valueOf(2L);

   /** The canonical name of the protocol. */
   protected String name;

   /** Whether the instance is initialised or not. */
   protected boolean initialised = false;

   /** The current step index of the protocol exchange. */
   protected int step = -1;

   /** Whether the exchange has concluded or not. */
   protected boolean complete = false;

   /** The optional {@link SecureRandom} instance to use. */
   protected SecureRandom rnd = null;

   /** The optional {@link IRandom} instance to use. */
   protected IRandom irnd = null;

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

   protected BaseKeyAgreementParty(String name) {
      super();

      this.name = name;
   }

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

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

   public String name() {
      return name;
   }

   public void init(Map attributes) throws KeyAgreementException {
      if (initialised) {
         throw new IllegalStateException("already initialised");
      }

      this.engineInit(attributes);

      initialised = true;
      this.step = -1;
      this.complete = false;
   }

   public OutgoingMessage processMessage(IncomingMessage in)
   throws KeyAgreementException {
      if (!initialised) {
         throw new IllegalStateException("not initialised");
      }
      if (complete) {
         throw new IllegalStateException("exchange has already concluded");
      }

      step++;
      return this.engineProcessMessage(in);
   }

   public boolean isComplete() {
      return complete;
   }

   public byte[] getSharedSecret() throws KeyAgreementException {
      if (!initialised) {
         throw new KeyAgreementException("not yet initialised");
      }
      if (!isComplete()) {
         throw new KeyAgreementException("not yet computed");
      }
      return engineSharedSecret();
   }

   public void reset() {
      if (initialised) {
         this.engineReset();
         initialised = false;
      }
   }

   // abstract methods to be implemented by concrete subclasses ---------------

   protected abstract void engineInit(Map attributes) throws KeyAgreementException;

   protected abstract OutgoingMessage engineProcessMessage(IncomingMessage in)
   throws KeyAgreementException;

   protected abstract byte[] engineSharedSecret() throws KeyAgreementException;

   protected abstract void engineReset();

   // helper methods ----------------------------------------------------------

   /**
    * Fills the designated byte array with random data.
    *
    * @param buffer the byte array to fill with random data.
    */
   protected void nextRandomBytes(byte[] buffer) {
      if (rnd != null) {
         rnd.nextBytes(buffer);
      } else if (irnd != null) {
         try {
            irnd.nextBytes(buffer, 0, buffer.length);
         } catch (LimitReachedException lre) {
            irnd = null;
            PRNG.nextBytes(buffer);
         }
      } else {
         PRNG.nextBytes(buffer);
      }
   }
}