/* 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.

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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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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
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permission to link this library with independent modules to produce an
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package gnu.java.security.key.dss;

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 StringBuilder(this.getClass().getName()).append("(")
            .append(super.toString()).append(",").append(ls)
            .append("y=0x").append(y.toString(16)).append(ls)
            .append(")")
            .toString();
      }
    return str;
  }
}