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SRPPublicKey.java

package gnu.crypto.key.srp6;

// ----------------------------------------------------------------------------
// $Id: SRPPublicKey.java,v 1.1 2003/09/26 23:50:48 raif 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.,
//    59 Temple Place - Suite 330,
//    Boston, MA 02111-1307
//    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.key.IKeyPairCodec;
import gnu.crypto.Registry;

import java.math.BigInteger;
import java.security.PublicKey;

/**
 * <p>A representation of an SRP ephemeral public key.</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: 1.1 $
 */
00063 public class SRPPublicKey extends SRPKey implements PublicKey {

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

      /**
       * The public exponent for either the server or the client engaged in the
       * SRP protocol exchange.
       */
00072       private final BigInteger Y;

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

   /**
    * <p>Public constructor for use from outside this package.</p>
    *
    * @param N the public shared modulus.
    * @param g the generator.
    * @param Y the public exponent of the ephemeral key.
    */
00084       public SRPPublicKey(BigInteger N, BigInteger g, BigInteger Y) {
            super(N, g);

      SRPAlgorithm.checkParams(N, g);
            this.Y = Y;
      }

   /**
    * <p>Default constructor. Assumes that N and g are already validated.</p>
    *
    * @param params an array of 3 values representing N, g and Y; the latter
    * being the client's or server's public exponent.
    */
00097    SRPPublicKey(BigInteger[] params) {
      super(params[0], params[1]);

      this.Y = params[2];
   }

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

   /**
    * <p>A class method that takes the output of the <code>encodePublicKey()</code>
    * method of an SRP keypair codec object (an instance implementing
    * {@link IKeyPairCodec} for SRP keys, and re-constructs an instance of this
    * object.</p>
    *
    * @param k the contents of a previously encoded instance of this object.
    * @throws ArrayIndexOutOfBoundsException if there is not enough bytes, in
    * <code>k</code>, to represent a valid encoding of an instance of this object.
    * @throws IllegalArgumentException if the byte sequence does not represent a
    * valid encoding of an instance of this object.
    */
00118    public static SRPPublicKey valueOf(byte[] k) {
      // check magic...
      // we should parse here enough bytes to know which codec to use, and
      // direct the byte array to the appropriate codec.  since we only have one
      // codec, we could have immediately tried it; nevertheless since testing
      // one byte is cheaper than instatiating a codec that will fail we test
      // the first byte before we carry on.
      if (k[0] == Registry.MAGIC_RAW_SRP_PUBLIC_KEY[0]) {
         // it's likely to be in raw format. get a raw codec and hand it over
         IKeyPairCodec codec = new SRPKeyPairRawCodec();
         return (SRPPublicKey) codec.decodePublicKey(k);
      } else {
         throw new IllegalArgumentException("magic");
      }
   }

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

      /**
       * <p>Returns the public exponent of the key as a {@link BigInteger}.</p>
       *
       * @return the public exponent of the key as a {@link BigInteger}.
       */
00142       public BigInteger getY() {
            return Y;
      }

   // Other instance methods --------------------------------------------------

   /**
    * <p>Returns the encoded form of this public key according to the designated
    * format.</p>
    *
    * @param format the desired format identifier of the resulting encoding.
    * @return the byte sequence encoding this key according to the designated
    * format.
    * @throws IllegalArgumentException if the format is not supported.
    */
00157    public byte[] getEncoded(int format) {
      byte[] result;
      switch (format) {
      case IKeyPairCodec.RAW_FORMAT:
         result = new SRPKeyPairRawCodec().encodePublicKey(this);
         break;
      default:
         throw new IllegalArgumentException("format");
      }
      return result;
   }

   /**
    * <p>Returns <code>true</code> if the designated object is an instance of
    * <code>SRPPublicKey</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.
    */
00178    public boolean equals(Object obj) {
      if (obj == null) {
         return false;
      }
      if (!(obj instanceof SRPPublicKey)) {
         return false;
      }
      SRPPublicKey that = (SRPPublicKey) obj;
      return super.equals(that) && Y.equals(that.getY());
   }
}

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