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/* DSSPublicKey.java --
   Copyright 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
 
This file is a part of GNU Classpath.
 
GNU Classpath 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 of the License, or (at
your option) any later version.
 
GNU Classpath 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 GNU Classpath; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, 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.  */
 
 
package gnu.java.security.key.dss;
 
import gnu.java.lang.CPStringBuilder;
 
import gnu.java.security.Registry;
import gnu.java.security.action.GetPropertyAction;
import gnu.java.security.key.IKeyPairCodec;
 
import java.math.BigInteger;
import java.security.AccessController;
import java.security.PublicKey;
import java.security.interfaces.DSAPublicKey;
 
/**
 * An object that embodies a DSS (Digital Signature Standard) public key.
 *
 * @see #getEncoded
 */
public class DSSPublicKey
    extends DSSKey
    implements PublicKey, DSAPublicKey
{
  /**
   * <code>y = g<sup>x</sup> mod p</code> where <code>x</code> is the
   * private part of the DSA key.
   */
  private final BigInteger y;
 
  /** String representation of this key. Cached for speed. */
  private transient String str;
 
  /**
   * Conveience constructor. Calls the constructor with 5 arguments passing
   * {@link Registry#RAW_ENCODING_ID} as the identifier of the preferred
   * encoding format.
   *
   * @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.
   */
  public DSSPublicKey(BigInteger p, BigInteger q, BigInteger g, BigInteger y)
  {
    this(Registry.RAW_ENCODING_ID, p, q, g, y);
  }
 
  /**
   * Constructs a new instance of <code>DSSPublicKey</code> given the
   * designated arguments.
   *
   * @param preferredFormat the identifier of the preferred encoding format to
   *          use when externalizing this key.
   * @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.
   */
  public DSSPublicKey(int preferredFormat, BigInteger p, BigInteger q,
                      BigInteger g, BigInteger y)
  {
    super(preferredFormat == Registry.ASN1_ENCODING_ID ? Registry.X509_ENCODING_ID
                                                       : preferredFormat,
          p, q, g);
    this.y = y;
  }
 
  /**
   * A class method that takes the output of the <code>encodePublicKey()</code>
   * method of a DSS keypair codec object (an instance implementing
   * {@link gnu.java.security.key.IKeyPairCodec} for DSS keys, and re-constructs
   * an instance of this object.
   *
   * @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 DSSPublicKey valueOf(byte[] k)
  {
    // try RAW codec
    if (k[0] == Registry.MAGIC_RAW_DSS_PUBLIC_KEY[0])
      try
        {
          return (DSSPublicKey) new DSSKeyPairRawCodec().decodePublicKey(k);
        }
      catch (IllegalArgumentException ignored)
        {
        }
    // try X.509 codec
    return (DSSPublicKey) new DSSKeyPairX509Codec().decodePublicKey(k);
  }
 
  public BigInteger getY()
  {
    return y;
  }
 
  /**
   * Returns the encoded form of this public key according to the designated
   * format.
   *
   * @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().encodePublicKey(this);
        break;
      case IKeyPairCodec.X509_FORMAT:
        result = new DSSKeyPairX509Codec().encodePublicKey(this);
        break;
      default:
        throw new IllegalArgumentException("Unsupported encoding format: "
                                           + format);
      }
    return result;
  }
 
  /**
   * 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.
   *
   * @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 DSAPublicKey))
      return false;
 
    DSAPublicKey that = (DSAPublicKey) obj;
    return super.equals(that) && y.equals(that.getY());
  }
 
  public String toString()
  {
    if (str == null)
      {
        String ls = (String) AccessController.doPrivileged
            (new GetPropertyAction("line.separator"));
        str = new CPStringBuilder(this.getClass().getName()).append("(")
            .append(super.toString()).append(",").append(ls)
            .append("y=0x").append(y.toString(16)).append(ls)
            .append(")")
            .toString();
      }
    return str;
  }
}