/* SRPPublicKey.java -- 
   Copyright (C) 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
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General Public License for more details.

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package gnu.javax.crypto.key.srp6;

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

import java.math.BigInteger;
import java.security.PublicKey;

/**
 * A representation of an SRP ephemeral public key.
 * <p>
 * Reference:
 * <ol>
 * <li><a href="http://srp.stanford.edu/design.html">SRP Protocol Design</a><br>
 * Thomas J. Wu.</li>
 * </ol>
 */
public class SRPPublicKey
    extends SRPKey
    implements PublicKey
{
  /**
   * The public exponent for either the server or the client engaged in the SRP
   * protocol exchange.
   */
  private final BigInteger Y;

  /**
   * Public constructor for use from outside this package.
   * 
   * @param N the public shared modulus.
   * @param g the generator.
   * @param Y the public exponent of the ephemeral key.
   */
  public SRPPublicKey(BigInteger N, BigInteger g, BigInteger Y)
  {
    super(N, g);

    SRPAlgorithm.checkParams(N, g);
    this.Y = Y;
  }

  /**
   * Default constructor. Assumes that N and g are already validated.
   * 
   * @param params an array of 3 values representing N, g and Y; the latter
   *          being the client's or server's public exponent.
   */
  SRPPublicKey(BigInteger[] params)
  {
    super(params[0], params[1]);

    this.Y = params[2];
  }

  /**
   * A class method that takes the output of the <code>encodePublicKey()</code>
   * method of an SRP keypair codec object (an instance implementing
   * {@link IKeyPairCodec} for SRP keys, and re-constructs an instance of this
   * object.
   * 
   * @param k the contents of a previously encoded instance of this object.
   * @throws ArrayIndexOutOfBoundsException if there is not enough bytes, in
   *           <code>k</code>, to represent a valid encoding of an instance
   *           of this object.
   * @throws IllegalArgumentException if the byte sequence does not represent a
   *           valid encoding of an instance of this object.
   */
  public static SRPPublicKey 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_SRP_PUBLIC_KEY[0])
      {
        // it's likely to be in raw format. get a raw codec and hand it over
        IKeyPairCodec codec = new SRPKeyPairRawCodec();
        return (SRPPublicKey) codec.decodePublicKey(k);
      }
    throw new IllegalArgumentException("magic");
  }

  /**
   * Returns the public exponent of the key as a {@link BigInteger}.
   * 
   * @return the public exponent of the key as a {@link BigInteger}.
   */
  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.
   * @throws IllegalArgumentException if the format is not supported.
   */
  public byte[] getEncoded(int format)
  {
    byte[] result;
    switch (format)
      {
      case IKeyPairCodec.RAW_FORMAT:
        result = new SRPKeyPairRawCodec().encodePublicKey(this);
        break;
      default:
        throw new IllegalArgumentException("format");
      }
    return result;
  }

  /**
   * Returns <code>true</code> if the designated object is an instance of
   * <code>SRPPublicKey</code>and has the same SRP parameter values as this
   * one.
   * 
   * @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 SRPPublicKey))
      return false;
    SRPPublicKey that = (SRPPublicKey) obj;
    return super.equals(that) && Y.equals(that.getY());
  }
}