/**
 * This file is part of aion-emu <aion-emu.com>.
 *
 *  aion-emu is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  aion-emu is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with aion-emu.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.aionemu.loginserver.network.ncrypt;

import java.math.BigInteger;
import java.security.KeyPair;
import java.security.interfaces.RSAPublicKey;

/**
 * This class is for storing standard RSA Public/Static keyPairs
 * The main difference that N (Modulus) is encrypted to be transfered
 * on the net with simple scrambling algorythm. So public pair (e, n)
 * , where e is exponent (usually static 3 or 65537) and n is modulus,
 * is encrypted and cannot be applied to cipher some data without deciphering
 * the modulus.
 *
 * @author EvilSpirit
 */
public class EncryptedRSAKeyPair
{
	/**
	 * KeyPair
	 */
	private KeyPair RSAKeyPair;
	/**
	 * Byte
	 */
	private byte[]	encryptedModulus;

    /**
     * Default constructor. Stores RSA key pair and encrypts rsa modulus N 
     * @param RSAKeyPair standard RSA KeyPair generated
     * with standard KeyPairGenerator {@link java.security.KeyPairGenerator}
     */
    public EncryptedRSAKeyPair(KeyPair RSAKeyPair)
	{
		this.RSAKeyPair = RSAKeyPair;
		encryptedModulus = encryptModulus(((RSAPublicKey) this.RSAKeyPair.getPublic()).getModulus());
	}

    /**
     * Encrypt RSA modulus N
     * @param modulus RSA modulus from public/private pairs (e,n), (d,n)
     * @return encrypted modulus
     */
	private byte[] encryptModulus(BigInteger modulus)
	{
		byte[]	encryptedModulus = modulus.toByteArray();

		if((encryptedModulus.length == 0x81) && (encryptedModulus[0] == 0x00))
		{
			byte[]	temp = new byte[0x80];

			System.arraycopy(encryptedModulus, 1, temp, 0, 0x80);

			encryptedModulus = temp;
		}

		for(int i = 0; i < 4; i++)
		{
			byte	temp = encryptedModulus[i];

			encryptedModulus[i]        = encryptedModulus[0x4d + i];
			encryptedModulus[0x4d + i] = temp;
		}

		for(int i = 0; i < 0x40; i++)
		{
			encryptedModulus[i] = (byte) (encryptedModulus[i] ^ encryptedModulus[0x40 + i]);
		}

		for(int i = 0; i < 4; i++)
		{
			encryptedModulus[0x0d + i] = (byte) (encryptedModulus[0x0d + i] ^ encryptedModulus[0x34 + i]);
		}

		for(int i = 0; i < 0x40; i++)
		{
			encryptedModulus[0x40 + i] = (byte) (encryptedModulus[0x40 + i] ^ encryptedModulus[i]);
		}

		return encryptedModulus;
	}

    /**
     * Get default RSA key pair
     * @return RSAKeyPair
     */
	public KeyPair getRSAKeyPair()
	{
		return RSAKeyPair;
	}

    /**
     * Get encrypted modulus to be transferred on the net.
     * @return encryptedModulus
     */
	public byte[] getEncryptedModulus()
	{
		return encryptedModulus;
	}
}