Java加密技术（二）

接下来我们介绍对称加密算法，最常用的莫过于DES数据加密算法。 
DES  
DES-Data Encryption Standard,即数据加密算法。是IBM公司于1975年研究成功并公开发表的。DES算法的入口参数有三个:Key、Data、Mode。其中Key为8个字节共64位,是DES算法的工作密钥;Data也为8个字节64位,是要被加密或被解密的数据;Mode为DES的工作方式,有两种:加密或解密。 
　　DES算法把64位的明文输入块变为64位的密文输出块,它所使用的密钥也是64位。 

通过java代码实现如下： Coder类见 Java加密技术（一）  

 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;


 /**
  * DES安全编码组件
  *
  * <pre>
  * 支持 DES、DESede(TripleDES,就是3DES)、AES、Blowfish、RC2、RC4(ARCFOUR)
  * DES                  key size must be equal to 56
  * DESede(TripleDES)    key size must be equal to 112 or 168
  * AES                  key size must be equal to 128, 192 or 256,but 192 and 256 bits may not be available
  * Blowfish             key size must be multiple of 8, and can only range from 32 to 448 (inclusive)
  * RC2                  key size must be between 40 and 1024 bits
  * RC4(ARCFOUR)         key size must be between 40 and 1024 bits
  * 具体内容 需要关注 JDK Document http://.../docs/technotes/guides/security/SunProviders.html
  * </pre>
  *
  * @author 梁栋
  * @version 1.0
  * @since 1.0
  */
 public abstract class DESCoder extends Coder {
     /**
      * ALGORITHM 算法 <br>
      * 可替换为以下任意一种算法，同时key值的size相应改变。
      *
      * <pre>
      * DES                  key size must be equal to 56
      * DESede(TripleDES)    key size must be equal to 112 or 168
      * AES                  key size must be equal to 128, 192 or 256,but 192 and 256 bits may not be available
      * Blowfish             key size must be multiple of 8, and can only range from 32 to 448 (inclusive)
      * RC2                  key size must be between 40 and 1024 bits
      * RC4(ARCFOUR)         key size must be between 40 and 1024 bits
      * </pre>
      *
      * 在Key toKey(byte[] key)方法中使用下述代码
      * <code>SecretKey secretKey = new SecretKeySpec(key, ALGORITHM);</code> 替换
      * <code>
      * DESKeySpec dks = new DESKeySpec(key);
      * SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(ALGORITHM);
      * SecretKey secretKey = keyFactory.generateSecret(dks);
      * </code>
      */
     public static final String ALGORITHM = "DES";

     /**
      * 转换密钥<br>
      *
      * @param key
      * @return
      * @throws Exception
      */
     private static Key toKey(byte[] key) throws Exception {
         DESKeySpec dks = new DESKeySpec(key);
         SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(ALGORITHM);
         SecretKey secretKey = keyFactory.generateSecret(dks);

         // 当使用其他对称加密算法时，如AES、Blowfish等算法时，用下述代码替换上述三行代码
         // SecretKey secretKey = new SecretKeySpec(key, ALGORITHM);

         return secretKey;
     }

     /**
      * 解密
      *
      * @param data
      * @param key
      * @return
      * @throws Exception
      */
     public static byte[] decrypt(byte[] data, String key) throws Exception {
         Key k = toKey(decryptBASE64(key));

         Cipher cipher = Cipher.getInstance(ALGORITHM);
         cipher.init(Cipher.DECRYPT_MODE, k);

         return cipher.doFinal(data);
     }

     /**
      * 加密
      *
      * @param data
      * @param key
      * @return
      * @throws Exception
      */
     public static byte[] encrypt(byte[] data, String key) throws Exception {
         Key k = toKey(decryptBASE64(key));
         Cipher cipher = Cipher.getInstance(ALGORITHM);
         cipher.init(Cipher.ENCRYPT_MODE, k);

         return cipher.doFinal(data);
     }

     /**
      * 生成密钥
      *
      * @return
      * @throws Exception
      */
     public static String initKey() throws Exception {
         return initKey(null);
     }

     /**
      * 生成密钥
      *
      * @param seed
      * @return
      * @throws Exception
      */
     public static String initKey(String seed) throws Exception {
         SecureRandom secureRandom = null;

         if (seed != null) {
             secureRandom = new SecureRandom(decryptBASE64(seed));
         } else {
             secureRandom = new SecureRandom();
         }

         KeyGenerator kg = KeyGenerator.getInstance(ALGORITHM);
         kg.init(secureRandom);

         SecretKey secretKey = kg.generateKey();

         return encryptBASE64(secretKey.getEncoded());
     }
 }

延续上一个类的实现，我们通过MD5以及SHA对字符串加密生成密钥，这是比较常见的密钥生成方式。 
再给出一个测试类： 

 import static org.junit.Assert.*;


 import org.junit.Test;

 /**
  *
  * @author 梁栋
  * @version 1.0
  * @since 1.0
  */
 public class DESCoderTest {

     @Test
     public void test() throws Exception {
         String inputStr = "DES";
         String key = DESCoder.initKey();
         System.err.println("原文:\t" + inputStr);

         System.err.println("密钥:\t" + key);

         byte[] inputData = inputStr.getBytes();
         inputData = DESCoder.encrypt(inputData, key);

         System.err.println("加密后:\t" + DESCoder.encryptBASE64(inputData));

         byte[] outputData = DESCoder.decrypt(inputData, key);
         String outputStr = new String(outputData);

         System.err.println("解密后:\t" + outputStr);

         assertEquals(inputStr, outputStr);
     }
 }

得到的输出内容如下： 

 原文: DES
 密钥: f3wEtRrV6q0=

 加密后:    C6qe9oNIzRY=

 解密后:    DES

    由控制台得到的输出，我们能够比对加密、解密后结果一致。这是一种简单的加密解密方式，只有一个密钥。 
    其实DES有很多同胞兄弟，如DESede(TripleDES)、AES、Blowfish、RC2、RC4(ARCFOUR)。这里就不过多阐述了，大同小异，只要换掉ALGORITHM换成对应的值，同时做一个代码替换 SecretKey secretKey = new SecretKeySpec(key, ALGORITHM); 就可以了，此外就是密钥长度不同了。 

 /**
  * DES          key size must be equal to 56
  * DESede(TripleDES) key size must be equal to 112 or 168
  * AES          key size must be equal to 128, 192 or 256,but 192 and 256 bits may not be available
  * Blowfish     key size must be multiple of 8, and can only range from 32 to 448 (inclusive)
  * RC2          key size must be between 40 and 1024 bits
  * RC4(ARCFOUR) key size must be between 40 and 1024 bits
  **/