密钥加密解密

最近闲来无事..稍稍的研究了下java安全.说到安全 加密->解密 数字摘要MD5/SHA算法 数字签名，数字证书等..

   密钥加密

package org.deepsap.security;

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

/***
 * 
 * @author WeiJ
 * 
 */

public class PrivateKeyTest {
	public static void main(String[] args) throws Exception {

		byte[] plainText = "这只是一个奇迹".getBytes("UTF8");

		// 得到DES私钥
		System.out.println("\n开始生成AES私钥");
		long beginTime = System.currentTimeMillis();
		Key key = KeyGenerator.getInstance("AES").generateKey();
		System.out.println("生成DES私钥已完成,耗时共"
				+ (System.currentTimeMillis() - beginTime) + "ms");

		// 得到AES cipher 对象，并打印出算法的提供者
		Cipher cipher = Cipher.getInstance("AES");
		System.out.println("\n" + cipher.getProvider().getInfo());
		// 使用密钥对文本进行加密
		System.out.println("\n开始加密");
		// 加密之前需先初始化Cipher
		cipher.init(Cipher.ENCRYPT_MODE, key);
		byte[] result = cipher.doFinal(plainText);
		System.out.println("\n完成加密");
		System.out.println("加密后的:" + new String(result, "UTF8"));

		// 使用同一把密钥对密文进行解密
		System.out.println("\n开始解密");
		cipher.init(Cipher.DECRYPT_MODE, key);
		byte[] newResult = cipher.doFinal(result);
		System.out.println("完成解密: ");
		System.out.println(new String(newResult, "UTF8"));
	}
}

如果不初始化的会抛这么个异常

Exception in thread "main" java.lang.IllegalStateException: Cipher not initialized
	at javax.crypto.Cipher.c(DashoA13*..)
	at javax.crypto.Cipher.doFinal(DashoA13*..)
	at org.deepsap.security.PrivateKeyTest.main(PrivateKeyTest.java:31)