package gnu.crypto.key.dss;

// ----------------------------------------------------------------------------
// $Id: DSSPrivateKey.java,v 1.2 2005/10/06 04:24:16 rsdio 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.
//
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// 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.
//
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// along with this program; see the file COPYING.  If not, write to the
//
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//    USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
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// you permission to link this library with independent modules to
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// ----------------------------------------------------------------------------

import gnu.crypto.Registry;
import gnu.crypto.key.IKeyPairCodec;

import java.math.BigInteger;
import java.security.PrivateKey;
import java.security.interfaces.DSAPrivateKey;

/**
 * <p>An object that embodies a DSS (Digital Signature Standard) private key.</p>
 *
 * @version $Revision: 1.2 $
 * @see #getEncoded
 */
public class DSSPrivateKey extends DSSKey implements PrivateKey, DSAPrivateKey {

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

   /**
    * <p>A randomly or pseudorandomly generated integer with <code>0 &lt; x &lt;
    * q</code>.</p>
    */
   private final BigInteger x;

   // 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 x the private key part.
    */
   public DSSPrivateKey(BigInteger p, BigInteger q, BigInteger g, BigInteger x) {
      super(p, q, g);

      this.x = x;
   }

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

   /**
    * <p>A class method that takes the output of the <code>encodePrivateKey()</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.
    */
   public static DSSPrivateKey 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_PRIVATE_KEY[0]) {
         // it's likely to be in raw format. get a raw codec and hand it over
         IKeyPairCodec codec = new DSSKeyPairRawCodec();
         return (DSSPrivateKey) codec.decodePrivateKey(k);
      } else {
         throw new IllegalArgumentException("magic");
      }
   }

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

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

   public BigInteger getX() {
      return x;
   }

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

   /**
    * <p>Returns the encoded form of this private 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
    */
   public byte[] getEncoded(int format) {
      byte[] result;
      switch (format) {
      case IKeyPairCodec.RAW_FORMAT:
         result = new DSSKeyPairRawCodec().encodePrivateKey(this);
         break;
      default:
         throw new IllegalArgumentException("format");
      }
      return result;
   }

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