Java加密技术（五）

接下来我们分析DH加密算法，一种适基于密钥一致协议的加密算法。 
DH  
Diffie-Hellman算法(D-H算法)，密钥一致协议。是由公开密钥密码体制的奠基人Diffie和Hellman所提出的一种思想。简单的说就是允许两名用户在公开媒体上交换信息以生成"一致"的、可以共享的密钥。换句话说，就是由甲方产出一对密钥（公钥、私钥），乙方依照甲方公钥产生乙方密钥对（公钥、私钥）。以此为基线，作为数据传输保密基础，同时双方使用同一种对称加密算法构建本地密钥（SecretKey）对数据加密。这样，在互通了本地密钥（SecretKey）算法后，甲乙双方公开自己的公钥，使用对方的公钥和刚才产生的私钥加密数据，同时可以使用对方的公钥和自己的私钥对数据解密。不单单是甲乙双方两方，可以扩展为多方共享数据通讯，这样就完成了网络交互数据的安全通讯！该算法源于中国的同余定理——中国馀数定理。   

流程分析： 

1.甲方构建密钥对儿，将公钥公布给乙方，将私钥保留；双方约定数据加密算法；乙方通过甲方公钥构建密钥对儿，将公钥公布给甲方，将私钥保留。 
2.甲方使用私钥、乙方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥加密数据，发送给乙方加密后的数据；乙方使用私钥、甲方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥对数据解密。 
3.乙方使用私钥、甲方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥加密数据，发送给甲方加密后的数据；甲方使用私钥、乙方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥对数据解密。 

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.KeyFactory;
 import java.security.KeyPair;
 import java.security.KeyPairGenerator;
 import java.security.PublicKey;
 import java.security.spec.PKCS8EncodedKeySpec;
 import java.security.spec.X509EncodedKeySpec;
 import java.util.HashMap;
 import java.util.Map;

 import javax.crypto.Cipher;
 import javax.crypto.KeyAgreement;
 import javax.crypto.SecretKey;
 import javax.crypto.interfaces.DHPrivateKey;
 import javax.crypto.interfaces.DHPublicKey;
 import javax.crypto.spec.DHParameterSpec;

 /**
  * DH安全编码组件
  *
  * @author 梁栋
  * @version 1.0
  * @since 1.0
  */
 public abstract class DHCoder extends Coder {
     public static final String ALGORITHM = "DH";

     /**
      * 默认密钥字节数
      *
      * <pre>
      * DH
      * Default Keysize 1024
      * Keysize must be a multiple of 64, ranging from 512 to 1024 (inclusive).
      * </pre>
      */
     private static final int KEY_SIZE = 1024;

     /**
      * DH加密下需要一种对称加密算法对数据加密，这里我们使用DES，也可以使用其他对称加密算法。
      */
     public static final String SECRET_ALGORITHM = "DES";
     private static final String PUBLIC_KEY = "DHPublicKey";
     private static final String PRIVATE_KEY = "DHPrivateKey";

     /**
      * 初始化甲方密钥
      *
      * @return
      * @throws Exception
      */
     public static Map<String, Object> initKey() throws Exception {
         KeyPairGenerator keyPairGenerator = KeyPairGenerator
                 .getInstance(ALGORITHM);
         keyPairGenerator.initialize(KEY_SIZE);

         KeyPair keyPair = keyPairGenerator.generateKeyPair();

         // 甲方公钥
         DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();

         // 甲方私钥
         DHPrivateKey privateKey = (DHPrivateKey) keyPair.getPrivate();

         Map<String, Object> keyMap = new HashMap<String, Object>(2);

         keyMap.put(PUBLIC_KEY, publicKey);
         keyMap.put(PRIVATE_KEY, privateKey);
         return keyMap;
     }

     /**
      * 初始化乙方密钥
      *
      * @param key
      *            甲方公钥
      * @return
      * @throws Exception
      */
     public static Map<String, Object> initKey(String key) throws Exception {
         // 解析甲方公钥
         byte[] keyBytes = decryptBASE64(key);
         X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);

         // 由甲方公钥构建乙方密钥
         DHParameterSpec dhParamSpec = ((DHPublicKey) pubKey).getParams();

         KeyPairGenerator keyPairGenerator = KeyPairGenerator
                 .getInstance(keyFactory.getAlgorithm());
         keyPairGenerator.initialize(dhParamSpec);

         KeyPair keyPair = keyPairGenerator.generateKeyPair();

         // 乙方公钥
         DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();

         // 乙方私钥
         DHPrivateKey privateKey = (DHPrivateKey) keyPair.getPrivate();

         Map<String, Object> keyMap = new HashMap<String, Object>(2);

         keyMap.put(PUBLIC_KEY, publicKey);
         keyMap.put(PRIVATE_KEY, privateKey);

         return keyMap;
     }

     /**
      * 加密<br>
      *
      * @param data
      *            待加密数据
      * @param publicKey
      *            甲方公钥
      * @param privateKey
      *            乙方私钥
      * @return
      * @throws Exception
      */
     public static byte[] encrypt(byte[] data, String publicKey,
             String privateKey) throws Exception {

         // 生成本地密钥
         SecretKey secretKey = getSecretKey(publicKey, privateKey);

         // 数据加密
         Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
         cipher.init(Cipher.ENCRYPT_MODE, secretKey);

         return cipher.doFinal(data);
     }

     /**
      * 解密<br>
      *
      * @param data
      *            待解密数据
      * @param publicKey
      *            乙方公钥
      * @param privateKey
      *            乙方私钥
      * @return
      * @throws Exception
      */
     public static byte[] decrypt(byte[] data, String publicKey,
             String privateKey) throws Exception {

         // 生成本地密钥
         SecretKey secretKey = getSecretKey(publicKey, privateKey);
         // 数据解密
         Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
         cipher.init(Cipher.DECRYPT_MODE, secretKey);

         return cipher.doFinal(data);
     }

     /**
      * 构建密钥
      *
      * @param publicKey
      *            公钥
      * @param privateKey
      *            私钥
      * @return
      * @throws Exception
      */
     private static SecretKey getSecretKey(String publicKey, String privateKey)
             throws Exception {
         // 初始化公钥
         byte[] pubKeyBytes = decryptBASE64(publicKey);

         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(pubKeyBytes);
         PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);

         // 初始化私钥
         byte[] priKeyBytes = decryptBASE64(privateKey);

         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(priKeyBytes);
         Key priKey = keyFactory.generatePrivate(pkcs8KeySpec);

         KeyAgreement keyAgree = KeyAgreement.getInstance(keyFactory
                 .getAlgorithm());
         keyAgree.init(priKey);
         keyAgree.doPhase(pubKey, true);

         // 生成本地密钥
         SecretKey secretKey = keyAgree.generateSecret(SECRET_ALGORITHM);

         return secretKey;
     }

     /**
      * 取得私钥
      *
      * @param keyMap
      * @return
      * @throws Exception
      */
     public static String getPrivateKey(Map<String, Object> keyMap)
             throws Exception {
         Key key = (Key) keyMap.get(PRIVATE_KEY);

         return encryptBASE64(key.getEncoded());
     }

     /**
      * 取得公钥
      *
      * @param keyMap
      * @return
      * @throws Exception
      */
     public static String getPublicKey(Map<String, Object> keyMap)
             throws Exception {
         Key key = (Key) keyMap.get(PUBLIC_KEY);

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

再给出一个测试类： 

 import static org.junit.Assert.*;

 import java.util.Map;

 import org.junit.Test;

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

     @Test
     public void test() throws Exception {
         // 生成甲方密钥对儿
         Map<String, Object> aKeyMap = DHCoder.initKey();
         String aPublicKey = DHCoder.getPublicKey(aKeyMap);
         String aPrivateKey = DHCoder.getPrivateKey(aKeyMap);

         System.err.println("甲方公钥:\r" + aPublicKey);
         System.err.println("甲方私钥:\r" + aPrivateKey);

         // 由甲方公钥产生本地密钥对儿
         Map<String, Object> bKeyMap = DHCoder.initKey(aPublicKey);
         String bPublicKey = DHCoder.getPublicKey(bKeyMap);
         String bPrivateKey = DHCoder.getPrivateKey(bKeyMap);

         System.err.println("乙方公钥:\r" + bPublicKey);
         System.err.println("乙方私钥:\r" + bPrivateKey);

         String aInput = "abc ";
         System.err.println("原文: " + aInput);

         // 由甲方公钥，乙方私钥构建密文
         byte[] aCode = DHCoder.encrypt(aInput.getBytes(), aPublicKey,
                 bPrivateKey);

         // 由乙方公钥，甲方私钥解密
         byte[] aDecode = DHCoder.decrypt(aCode, bPublicKey, aPrivateKey);
         String aOutput = (new String(aDecode));

         System.err.println("解密: " + aOutput);

         assertEquals(aInput, aOutput);

         System.err.println(" ===============反过来加密解密================== ");
         String bInput = "def ";
         System.err.println("原文: " + bInput);

         // 由乙方公钥，甲方私钥构建密文
         byte[] bCode = DHCoder.encrypt(bInput.getBytes(), bPublicKey,
                 aPrivateKey);

         // 由甲方公钥，乙方私钥解密
         byte[] bDecode = DHCoder.decrypt(bCode, aPublicKey, bPrivateKey);
         String bOutput = (new String(bDecode));

         System.err.println("解密: " + bOutput);

         assertEquals(bInput, bOutput);
     }

 }

控制台输出： 

 甲方公钥:
 MIHfMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYXrgHz
 W5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpDTWSG
 kx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgANDAAJAdAWBVmIzqcko
 Ej6qFjLDL2+Y3FPq1iRbnOyOpDj71yKaK1K+FhTv04B0zy4DKcvAASV7/Gv0W+bgqdmffRkqrQ==

 甲方私钥:
 MIHRAgEAMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYX
 rgHzW5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpD
 TWSGkx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgAQyAjACJRfy1LyR
 eHyD+4Hfb+xR0uoIGR1oL9i9Nk6g2AAuaDPgEVWHn+QXID13yL/uDos=

 乙方公钥:
 MIHfMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYXrgHz
 W5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpDTWSG
 kx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgANDAAJAVEYSfBA+I9nr
 dWw3OBv475C+eBrWBBYqt0m6/eu4ptuDQHwV4MmUtKAC2wc2nNrdb1wmBhY1X8RnWkJ1XmdDbQ==

 乙方私钥:
 MIHSAgEAMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYX
 rgHzW5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpD
 TWSGkx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgAQzAjEAqaZiCdXp
 2iNpdBlHRaO9ir70wo2n32xNlIzIX19VLSPCDdeUWkgRv4CEj/8k+/yd

 原文: abc
 解密: abc
  ===============反过来加密解密==================
 原文: def
 解密: def

如我所言，甲乙双方在获得对方公钥后可以对发送给对方的数据加密，同时也能对接收到的数据解密，达到了数据安全通信的目的！