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

This file is a part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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package gnu.javax.crypto.key.srp6;

import gnu.java.security.Registry;
import gnu.java.security.key.IKeyPairCodec;

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

/**
 * <p>An abstract representation of a base SRP ephemeral key.</p>
 *
 * <p>This object encapsulates the two numbers:</p>
 * <ul>
 *    <li><b>N</b>: A large safe prime (N = 2q+1, where q is prime).</li>
 *    <li><b>g</b>: A generator modulo N.</li>
 * </ul>
 *
 * <p>Note that in SRP, all arithmetic is done modulo N.</p>
 *
 * <p>Reference:</p>
 * <ol>
 *    <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
 *    Thomas J. Wu.</li>
 * </ol>
 */
public abstract class SRPKey implements Key, Serializable
{

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

  /** The public, Germaine prime, shared modulus. */
  protected final BigInteger N;

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

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

  protected SRPKey(BigInteger N, BigInteger g)
  {
    super();

    this.N = N;
    this.g = g;
  }

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

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

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

  /**
   * <p>Returns the standard algorithm name for this key.</p>
   *
   * @return the standard algorithm name for this key.
   */
  public String getAlgorithm()
  {
    return Registry.SRP_KPG;
  }

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

  /**
   * Returns {@link Registry#RAW_ENCODING_SHORT_NAME} which is the sole format
   * supported for this type of keys.
   *
   * @return {@link Registry#RAW_ENCODING_SHORT_NAME} ALWAYS.
   */
  public String getFormat()
  {
    return Registry.RAW_ENCODING_SHORT_NAME;
  }

  // other methods -----------------------------------------------------------

  /**
   * <p>Returns the public shared modulus.</p>
   *
   * @return <code>N</code>.
   */
  public BigInteger getN()
  {
    return N;
  }

  /**
   * <p>Returns the generator.</p>
   *
   * @return <code>g</code>.
   */
  public BigInteger getG()
  {
    return g;
  }

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

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

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