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DSSPublicKey.java

package gnu.crypto.key.dss;

// ----------------------------------------------------------------------------
// $Id: DSSPublicKey.java,v 1.1 2003/09/26 23:50:48 raif Exp $
//
// Copyright (C) 2001, 2002, 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.Registry;
import gnu.crypto.key.IKeyPairCodec;

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

/**
 * <p>An object that embodies a DSS (Digital Signature Standard) public key.</p>
 *
 * @version $Revision: 1.1 $
 * @see #getEncoded
 */
00059 public class DSSPublicKey extends DSSKey implements PublicKey, DSAPublicKey {

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

   /**
    * <code>y = g<sup>x</sup> mod p</code> where <code>x</code> is the private
    * part of the DSA key.
    */
00068    private final BigInteger y;

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

   /**
    * <p>Trivial constructor.</p>
    *
    * @param p the public modulus.
    * @param q the public prime divisor of <code>p-1</code>.
    * @param g a generator of the unique cyclic group <code>Z<sup>*</sup>
    * <sub>p</sub></code>.
    * @param y the public key part.
    */
00082    public DSSPublicKey(BigInteger p, BigInteger q, BigInteger g, BigInteger y) {
      super(p, q, g);

      this.y = y;
   }

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

   /**
    * <p>A class method that takes the output of the <code>encodePublicKey()</code>
    * method of a DSS keypair codec object (an instance implementing
    * {@link gnu.crypto.key.IKeyPairCodec} for DSS keys, and re-constructs an
    * instance of this object.</p>
    *
    * @param k the contents of a previously encoded instance of this object.
    * @exception ArrayIndexOutOfBoundsException if there is not enough bytes,
    * in <code>k</code>, to represent a valid encoding of an instance of
    * this object.
    * @exception IllegalArgumentException if the byte sequence does not
    * represent a valid encoding of an instance of this object.
    */
00104    public static DSSPublicKey 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_DSS_PUBLIC_KEY[0]) {
         // it's likely to be in raw format. get a raw codec and hand it over
         IKeyPairCodec codec = new DSSKeyPairRawCodec();
         return (DSSPublicKey) codec.decodePublicKey(k);
      } else {
         throw new IllegalArgumentException("magic");
      }
   }

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

   // java.security.interfaces.DSAPublicKey interface implementation ----------

   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.
    * @exception IllegalArgumentException if the format is not supported.
    * @see DSSKeyPairRawCodec
    */
00141    public byte[] getEncoded(int format) {
      byte[] result;
      switch (format) {
      case IKeyPairCodec.RAW_FORMAT:
         result = new DSSKeyPairRawCodec().encodePublicKey(this);
         break;
      default:
         throw new IllegalArgumentException("format");
      }
      return result;
   }

   /**
    * <p>Returns <code>true</code> if the designated object is an instance of
    * {@link DSAPublicKey} and has the same DSS (Digital Signature Standard)
    * parameter values as this one.</p>
    *
    * @param obj the other non-null DSS key to compare to.
    * @return <code>true</code> if the designated object is of the same type and
    * value as this one.
    */
00162    public boolean equals(Object obj) {
      if (obj == null) {
         return false;
      }
      if (!(obj instanceof DSAPublicKey)) {
         return false;
      }
      DSAPublicKey that = (DSAPublicKey) obj;
      return super.equals(that) && y.equals(that.getY());
   }
}

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