金鑰加密也稱為對稱加密，速度快，但加密和解密的鑰匙必須相同，只有通訊雙方才能知道鑰匙

package com.stone.security;

import java.security.Key;
import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESKeySpec;
import javax.crypto.spec.IvParameterSpec;

/**
 * DES 演算法		1972美國IBM研製，對稱加密演算法
 * @author stone
 * @date 2014-03-10 04:47:05
 */
public class DES {	
	// 演算法名稱
	public static final String KEY_ALGORITHM = "DES";
	// 演算法名稱/加密模式/填充方式
	public static final String CIPHER_ALGORITHM_ECB = "DES/ECB/PKCS5Padding";
	public static final String CIPHER_ALGORITHM_CBC = "DES/CBC/PKCS5Padding";
	
	public static void main(String[] args) throws Exception {
		/*
		 * 使用 ECB mode
		 * 金鑰生成器 生成金鑰
		 * ECB mode cannot use IV
		 */
		byte[] key = generateKey();	
		byte[] encrypt = encrypt("胃炎F#*（x）".getBytes(), key);
		System.out.println(new String(decrypt(encrypt, key)));
		
		
		/*
		 * 使用CBC mode
		 * 使用金鑰工廠生成金鑰，加密 解密
		 * iv: DES in CBC mode and RSA ciphers with OAEP encoding operation.
		 */
		DESKeySpec dks = new DESKeySpec(generateKey());
		SecretKeyFactory factory = SecretKeyFactory.getInstance(KEY_ALGORITHM);
		SecretKey secretKey = factory.generateSecret(dks);
		Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM_CBC);
		cipher.init(Cipher.ENCRYPT_MODE, secretKey, new IvParameterSpec(getIV()));
		byte[] enc = cipher.doFinal("胃炎A%F#*（x）".getBytes()); //加密
		
		cipher.init(Cipher.DECRYPT_MODE, secretKey, new IvParameterSpec(getIV()));
		byte[] dec = cipher.doFinal(enc); // 解密
		System.out.println(new String(dec));
	}
	
	static byte[] getIV() {
		String iv = "asdfivh7"; //IV length: must be 8 bytes long
		return iv.getBytes();
	}

	/**
	 * 生成金鑰
	 * 
	 * @return
	 * @throws Exception
	 */
	private static byte[] generateKey() throws Exception {
		KeyGenerator keyGenerator = KeyGenerator.getInstance(KEY_ALGORITHM);
		keyGenerator.init(56); //des 必須是56, 此初始方法不必須呼叫
		SecretKey secretKey = keyGenerator.generateKey();
		return secretKey.getEncoded();
	}

	/**
	 * 還原金鑰
	 * 
	 * @param key
	 * @return
	 * @throws Exception 
	 */
	private static Key toKey(byte[] key) throws Exception {
		DESKeySpec des = new DESKeySpec(key);
		SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(KEY_ALGORITHM);
		SecretKey secretKey = keyFactory.generateSecret(des);
		return secretKey;
	}
	
	/**
	 * 加密 
	 * @param data 原文
	 * @param key
	 * @return 密文
	 * @throws Exception
	 */
	public static byte[] encrypt(byte[] data, byte[] key) throws Exception {
		Key k = toKey(key);
		Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM_ECB);
		cipher.init(Cipher.ENCRYPT_MODE, k, new SecureRandom());
		return cipher.doFinal(data);
	}
	/**
	 * 解密
	 * @param data 密文
	 * @param key
	 * @return 明文、原文
	 * @throws Exception
	 */
	public static byte[] decrypt(byte[] data, byte[] key) throws Exception {
		Key k = toKey(key);
		Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM_ECB);
		cipher.init(Cipher.DECRYPT_MODE, k, new SecureRandom());
		return cipher.doFinal(data);
	}
}