/* SRPPrivateKey.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.math.BigInteger;
import java.security.PrivateKey;

/**
 * A representation of an SRP ephemeral private 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 SRPPrivateKey
    extends SRPKey
    implements PrivateKey
{
  /**
   * The private exponent for either the server or the client engaged in the SRP
   * protocol exchange.
   */
  private final BigInteger X;
  /**
   * The user's verifier (v) --for the server-- also computed at the client side
   * as g.modPow(x, N), where x is the hashed output of the user name and
   * password .
   */
  private final BigInteger v;

  /**
   * Public constructor for use from outside this package.
   * 
   * @param N the public shared modulus.
   * @param g the generator.
   * @param x the private exponent of the ephemeral key.
   */
  public SRPPrivateKey(BigInteger N, BigInteger g, BigInteger x)
  {
    this(N, g, x, null);
  }

  /**
   * Public constructor for use from outside this package.
   * 
   * @param N the public shared modulus.
   * @param g the generator.
   * @param x the private exponent of the ephemeral key.
   * @param v the user's verifier value (for the server side only).
   */
  public SRPPrivateKey(BigInteger N, BigInteger g, BigInteger x, BigInteger v)
  {
    super(N, g);

    SRPAlgorithm.checkParams(N, g);
    this.X = x;
    this.v = v;
  }

  /**
   * Default constructor. Assumes N and g are already validated.
   * 
   * @param params an array of either 3 or 4 values representing N, g, and
   *          either v and X for the server, or just X for the client. Those
   *          values represent the following:
   *          <ol>
   *          <li>v (server side): the user's verifier.</li>
   *          <li>X (both sides): the server's or client's ephemeral private
   *          exponent.</li>
   *          </ol>
   */
  SRPPrivateKey(BigInteger[] params)
  {
    super(params[0], params[1]);

    if (params.length == 3)
      {
        X = params[2];
        v = null;
      }
    else if (params.length == 4)
      {
        X = params[2];
        v = params[3];
      }
    else
      throw new IllegalArgumentException("invalid number of SRP parameters");
  }

  /**
   * A class method that takes the output of the <code>encodePrivateKey()</code>
   * method of an SRP keypair codec object (an instance implementing
   * {@link IKeyPairCodec} for DSS 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 SRPPrivateKey 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_PRIVATE_KEY[0])
      {
        // it's likely to be in raw format. get a raw codec and hand it over
        IKeyPairCodec codec = new SRPKeyPairRawCodec();
        return (SRPPrivateKey) codec.decodePrivateKey(k);
      }
    throw new IllegalArgumentException("magic");
  }

  /**
   * Returns the private exponent of the key as a {@link BigInteger}.
   * 
   * @return the private exponent of the key as a {@link BigInteger}.
   */
  public BigInteger getX()
  {
    return X;
  }

  /**
   * Returns the user's verifier as a {@link BigInteger}.
   * 
   * @return the user's verifier as a {@link BigInteger} if this is an SRP
   *         private key of a Host, or <code>null</code> if this is a private
   *         SRP key for a User.
   */
  public BigInteger getV()
  {
    return v;
  }

  /**
   * Returns the encoded form of this private 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().encodePrivateKey(this);
        break;
      default:
        throw new IllegalArgumentException("format");
      }
    return result;
  }

  /**
   * Returns <code>true</code> if the designated object is an instance of
   * <code>SRPPrivateKey</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 SRPPrivateKey))
      return false;
    SRPPrivateKey that = (SRPPrivateKey) obj;
    boolean result = super.equals(that) && X.equals(that.getX());
    if (v != null)
      result = result && v.equals(that.getV());
    return result;
  }
}