/* GnuDHKey.java -- 
   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

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package gnu.javax.crypto.key.dh;

import gnu.java.security.Registry;
import gnu.java.security.util.FormatUtil;

import java.math.BigInteger;
import java.security.Key;

import javax.crypto.interfaces.DHKey;
import javax.crypto.spec.DHParameterSpec;

/**
 * <p>A base asbtract class for both public and private Diffie-Hellman keys. It
 * encapsulates the two DH numbers: <code>p</code>, and <code>g</code>.</p>
 *
 * <p>According to the JDK, cryptographic <i>Keys</i> all have a <i>format</i>.
 * The format used in this implementation is called <i>Raw</i>, and basically
 * consists of the raw byte sequences of algorithm parameters. The exact order
 * of the byte sequences and the implementation details are given in each of
 * the relevant <code>getEncoded()</code> methods of each of the private and
 * public keys.</p>
 *
 * <p>Reference:</p>
 * <ol>
 *    <li><a href="http://www.ietf.org/rfc/rfc2631.txt">Diffie-Hellman Key
 *    Agreement Method</a><br>
 *    Eric Rescorla.</li>
 * </ol>
 */
public abstract class GnuDHKey implements Key, DHKey
{

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

  /** The public prime q. A prime divisor of p-1. */
  protected BigInteger q;

  /** The public prime p. */
  protected BigInteger p;

  /** The generator g. */
  protected BigInteger g;

  /**
   * Identifier of the default encoding format to use when externalizing the
   * key material.
   */
  protected final int defaultFormat;

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

  /**
   * Trivial protected constructor.
   * 
   * @param defaultFormat the identifier of the encoding format to use by
   *          default when externalizing the key.
   * @param q a prime divisor of p-1.
   * @param p the public prime.
   * @param g the generator of the group.
   */
  protected GnuDHKey(int defaultFormat, BigInteger q, BigInteger p, BigInteger g)
  {
    super();

    this.defaultFormat = defaultFormat <= 0 ? Registry.RAW_ENCODING_ID
                                            : defaultFormat;
    this.q = q;
    this.p = p;
    this.g = g;
  }

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

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

  // javax.crypto.interfaces.DHKey interface implementation ------------------

  public DHParameterSpec getParams()
  {
    if (q == null)
      {
        return new DHParameterSpec(p, g);
      }
    else
      {
        return new DHParameterSpec(p, g, q.bitLength());
      }
  }

  // java.security.Key interface implementation ------------------------------

  public String getAlgorithm()
  {
    return Registry.DH_KPG;
  }

  /** @deprecated see getEncoded(int). */
  public byte[] getEncoded()
  {
    return getEncoded(defaultFormat);
  }

  public String getFormat()
  {
    return FormatUtil.getEncodingShortName(defaultFormat);
  }

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

  public BigInteger getQ()
  {
    return q;
  }

  /**
   * <p>Returns <code>true</code> if the designated object is an instance of
   * {@link DHKey} and has the same Diffie-Hellman parameter values as this
   * one.</p>
   *
   * @param obj the other non-null DH 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 DHKey))
      {
        return false;
      }
    DHKey that = (DHKey) obj;
    return p.equals(that.getParams().getP())
           && g.equals(that.getParams().getG());
  }

  // abstract methods to be implemented by subclasses ------------------------

  public abstract byte[] getEncoded(int format);
}
