package gnu.crypto.key.srp6;

// ----------------------------------------------------------------------------
// $Id: SRPKey.java,v 1.2 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
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// independent modules, and to copy and distribute the resulting
// executable under terms of your choice, provided that you also meet,
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// 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.Registry;
import gnu.crypto.key.IKeyPairCodec;

import java.io.Serializable;
import java.math.BigInteger;
import java.security.Key;

/**
 * <p>An abstract representation of a base SRP ephemeral key.</p>
 *
 * <p>This object encapsulates the two numbers:</p>
 * <ul>
 *    <li><b>N</b>: A large safe prime (N = 2q+1, where q is prime).</li>
 *    <li><b>g</b>: A generator modulo N.</li>
 * </ul>
 *
 * <p>Note that in SRP, all arithmetic is done modulo N.</p>
 *
 * <p>Reference:</p>
 * <ol>
 *    <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
 *    Thomas J. Wu.</li>
 * </ol>
 *
 * @version $Revision: 1.2 $
 */
public abstract class SRPKey implements Key, Serializable {

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

	/** The public, Germaine prime, shared modulus. */
	protected final BigInteger N;

	/** The generator. */
	protected final BigInteger g;

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

	protected SRPKey(BigInteger N, BigInteger g) {
      super();

		this.N = N;
		this.g = g;
	}

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

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

	// java.security.Key interface implementation ------------------------------

	/**
	 * <p>Returns the standard algorithm name for this key.</p>
	 *
	 * @return the standard algorithm name for this key.
	 */
	public String getAlgorithm() {
		return Registry.SRP_KPG;
	}

   /** @deprecated see getEncoded(int). */
   public byte[] getEncoded() {
      return getEncoded(IKeyPairCodec.RAW_FORMAT);
   }

	/**
	 * <p>Returns <code>null</code> since this implementation does not encode SRP
    * keys.</p>
	 *
	 * @return null since this implementation does not encode SRP keys.
	 */
	public String getFormat() {
		return null;
	}

	// other methods -----------------------------------------------------------

	/**
	 * <p>Returns the public shared modulus.</p>
	 *
	 * @return <code>N</code>.
	 */
	public BigInteger getN() {
		return N;
	}

	/**
	 * <p>Returns the generator.</p>
	 *
	 * @return <code>g</code>.
	 */
	public BigInteger getG() {
		return g;
	}

   /**
    * <p>Returns <code>true</code> if the designated object is an instance of
    * <code>SRPKey</code> and has the same SRP parameter values as this one.</p>
    *
    * @param obj the other non-null SRP key to compare to.
    * @return <code>true</code> if the designated object is of the same type and
    * value as this one.
    */
   public boolean equals(Object obj) {
      if (obj == null) {
         return false;
      }
      if (!(obj instanceof SRPKey)) {
         return false;
      }
      SRPKey that = (SRPKey) obj;
      return N.equals(that.getN()) && g.equals(that.getG());
   }

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

   public abstract byte[] getEncoded(int format);
}