/*
 * Copyright (c) 2004 ???. All Rights Reserved.
 *
 * Version 1.0 , Created on 2004-3-10
 *
 */

/**
 * @author Devon
 */

import java.security.*;
import java.security.spec.*;
import javax.crypto.*;

public class PairKeyExample {

	public static void main(String argv[]) {
		try {
			String algorithm = "RSA"; //定義加密算法,可用 DES,DESede,Blowfish
			String message = "張三，你好，我是李四";

			//產生張三的密鑰對(keyPairZhang)
			KeyPairGenerator keyGeneratorZhang =
				KeyPairGenerator.getInstance(algorithm);  //指定采用的算法
			keyGeneratorZhang.initialize(1024); //指定密鑰長度為1024位
			KeyPair keyPairZhang = keyGeneratorZhang.generateKeyPair(); //產生密鑰對
			System.out.println("生成張三的公鑰對");

			// 張三生成公鑰(publicKeyZhang)并發送給李四,這里發送的是公鑰的數組字節
			byte[] publicKeyZhangEncode = keyPairZhang.getPublic().getEncoded();

			//通過網絡或磁盤等方式,把公鑰編碼傳送給李四
			//李四接收到張三編碼后的公鑰,將其解碼
			KeyFactory keyFacoryLi = KeyFactory.getInstance(algorithm);  //得到KeyFactory對象
			X509EncodedKeySpec x509KeySpec =
				new X509EncodedKeySpec(publicKeyZhangEncode);  //公鑰采用X.509編碼
			PublicKey publicKeyZhang = keyFacoryLi.generatePublic(x509KeySpec); //將公鑰的KeySpec對象轉換為公鑰
			System.out.println("李四成功解碼,得到張三的公鑰");

			//李四用張三的公鑰加密信息，并發送給李四
			Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");  //得到Cipher對象
			cipher.init(Cipher.ENCRYPT_MODE, publicKeyZhang);  //用張三的公鑰初始化Cipher對象
			byte[] cipherMessage = cipher.doFinal(message.getBytes());  //得到加密信息
			System.out.println("加密后信息：" + new String(cipherMessage));
			System.out.println("加密完成，發送給李四...");

			//張三用自己的私鑰解密從李四處收到的信息
			cipher.init(Cipher.DECRYPT_MODE, keyPairZhang.getPrivate()); //張三用其私鑰初始化Cipher對象
			byte[] originalMessage = cipher.doFinal(cipherMessage);  //得到解密后信息
			System.out.println("張三收到信息，解密后為：" + new String(originalMessage));
		} catch (Exception ex) {
			ex.printStackTrace();
		}
	}
}