package au.net.aba.crypto.provider;

/*
 * $Id: RSAKeyPairGenerator.java,v 1.9 1998/10/30 04:20:14 leachbj Exp $
 * $Author: leachbj $
 *
 * Copyright (C) 1996-1998 Australian Business Access Pty Ltd.
 * All rights reserved.
 * 
 * Use, modification, copying and distribution of this software is subject the
 * terms and conditions of the ABA Public Licence. See the file
 * "PUBLIC_LICENCE" for additional information.
 *
 * If you have not received a copy of the Public Licence, you must destroy all
 * copies of this file immediately. 
 *
 * $Source: /aba/CVSROOT/jdk1.1/src/au.net.aba/crypto/provider/RSAKeyPairGenerator.java,v $
 * $Revision: 1.9 $
 * $Date: 1998/10/30 04:20:14 $
 * $State: Exp $
 */

import java.math.*;
import java.security.*;

/**
 * A class for generating a random RSA public/private key pair.
 */
public class RSAKeyPairGenerator extends KeyPairGenerator
{
	public final static String ident = "$Id: RSAKeyPairGenerator.java,v 1.9 1998/10/30 04:20:14 leachbj Exp $";

	private static BigInteger one = BigInteger.valueOf(1);
	private static BigInteger two = BigInteger.valueOf(2);

	int		strength;
	SecureRandom	random;
	int		certainty = 20;

	/**
	 * basic constructor.
	 */
	public RSAKeyPairGenerator()
	{
		super("RSA");
	}
	/**
	 * Generates a RSA key pair.
	 *
	 * @return a RSA public/private key pair.
	 */
	public KeyPair generateKeyPair()
	{
		BigInteger	p, q, n, d, e, pSub1, qSub1, phi;

		/*
		 * Each part of the key should be half the given strength
		 */
		int keyStrength = (strength + 1) / 2;

		p = new BigInteger(keyStrength, certainty, random);

		do
		{
			/**
			 * Generate a random number of strength bits that is a
			 * probable prime with a certainty of 1 - 1/2**certainty.
			 */
			q = new BigInteger(keyStrength, certainty, random);
		}
		while (p.equals(q));		// just in case

		if (p.compareTo(q) < 0)
		{
			BigInteger      tmp = p;

			p = q;
			q = tmp;
		}

		n = p.multiply(q);

		pSub1 = p.subtract(one);
		qSub1 = q.subtract(one);
		phi = pSub1.multiply(qSub1);

		e = BigInteger.valueOf(0x11);

		while (!e.gcd(phi).equals(one))
		{
			e = e.add(two);
		}

		d = e.modInverse(phi);

		/*
		 * create the factors for the private key
		 */
		BigInteger	dP, dQ, qInv;

		dP = d.remainder(pSub1);
		dQ = d.remainder(qSub1);
		qInv = q.modInverse(p);

		/*
		 * create the keys
		 */
		RSAPubKey	pubKey;
		RSAPrivKeyCrt	privKey;

		pubKey = new RSAPubKey(n, e);
		privKey = new RSAPrivKeyCrt(n, e, d, p, q, dP, dQ, qInv);

		return new KeyPair(pubKey, privKey);
	}
	/**
	 * Initialises the key pair generator for a certain strength, using
	 * the default parameter set. 
	 *
	 * @param strength	the size of the key (in bits).
	 * @param random	a source of randomness.
	 */
	public void initialize(
		int		strength,
		SecureRandom	random)
	{
		this.strength = strength;
		this.random = random;
	}
}