Java加密技术篇（四）非对称加密算法RSA

RSA 
    这种算法1978年就出现了，它是第一个既能用于数据加密也能用于数字签名的算法。它易于理解和操作，也很流行。算法的名字以发明者的名字命名：Ron Rivest, AdiShamir 和Leonard Adleman。 
    这种加密算法的特点主要是密钥的变化，上文我们看到DES只有一个密钥。相当于只有一把钥匙，如果这把钥匙丢了，数据也就不安全了。RSA同时有两把钥匙，公钥与私钥。同时支持数字签名。数字签名的意义在于，对传输过来的数据进行校验。确保数据在传输工程中不被修改。

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。
2. 甲方使用私钥加密数据，然后用私钥对加密后的数据签名，发送给乙方签名以及加密后的数据；乙方使用公钥、签名来验证待解密数据是否有效，如果有效使用公钥对数据解密。
3. 乙方使用公钥加密数据，向甲方发送经过加密后的数据；甲方获得加密数据，通过私钥解密。

按如上步骤给出序列图，如下： 

通过java代码实现如下：

 package com.somnus.cipher;

 import java.io.InputStream;
 import java.security.Key;
 import java.security.KeyFactory;
 import java.security.KeyPair;
 import java.security.KeyPairGenerator;
 import java.security.PrivateKey;
 import java.security.PublicKey;
 import java.security.Signature;
 import java.security.interfaces.RSAPrivateKey;
 import java.security.interfaces.RSAPublicKey;
 import java.security.spec.PKCS8EncodedKeySpec;
 import java.security.spec.X509EncodedKeySpec;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;

 import javax.crypto.Cipher;

 import org.apache.commons.codec.binary.Base64;
 import org.apache.commons.codec.binary.Hex;

 /** 非对称加密算法RSA
  * @Title: RsaEncrypt.java
  * @Description: TODO
  * @author Somnus
  * @date 2015年6月5日 下午2:02:44
  * @version V1.0
  */
 public class RSAUtil {
     public static final String ALGORITHM = "RSA";
     public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

     private static final String PUBLIC_KEY = "RSAPublicKey";
     private static final String PRIVATE_KEY = "RSAPrivateKey";

     private static final String PUBLIC_KEY_PATH = "public.cer";
     private static final String PRIVATE_KEY_PATH = "private.key";

     /**
      * 用私钥对信息生成数字签名
      *
      * @param data
      *            加密数据
      * @param privateKey
      *            私钥
      * @return
      * @throws Exception
      */
     public static String sign(String data) throws Exception {
         // 解密由base64编码的私钥
         byte[] keyBytes = Base64.decodeBase64(getPrivateKey());
         // 构造PKCS8EncodedKeySpec对象
         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
         // ALGORITHM 指定的加密算法
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         // 取私钥匙对象
         PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);
         // 用私钥对信息生成数字签名
         Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
         signature.initSign(priKey);
         signature.update(Hex.decodeHex(data.toCharArray()));
         return Base64.encodeBase64String(signature.sign());
     }

     /**
      * 校验数字签名
      *
      * @param data
      *            加密数据
      * @param publicKey
      *            公钥
      * @param sign
      *            数字签名
      *
      * @return 校验成功返回true 失败返回false
      * @throws Exception
      *
      */
     public static boolean verify(String data,String sign)throws Exception {
         // 解密由base64编码的公钥
         byte[] keyBytes = Base64.decodeBase64(getPublicKey());
         // 构造X509EncodedKeySpec对象
         X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
         // ALGORITHM 指定的加密算法
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         // 取公钥匙对象
         PublicKey pubKey = keyFactory.generatePublic(keySpec);
         Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
         signature.initVerify(pubKey);
         signature.update(Hex.decodeHex(data.toCharArray()));
         // 验证签名是否正常
         return signature.verify(Base64.decodeBase64(sign));
     }

     /**
      * 解密<br>
      * 用私钥解密
      *
      * @param data
      * @return
      * @throws Exception
      */
     public static String decryptByPrivateKey(String data)throws Exception {
         // 对密钥解密
         byte[] keyBytes = Base64.decodeBase64(getPrivateKey());
         // 取得私钥
         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         Key privateKey = keyFactory.generatePrivate(pkcs8KeySpec);
         //初始化Cipher对象，设置为解密模式
         Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
         cipher.init(Cipher.DECRYPT_MODE, privateKey);
         // 执行解密操作
         byte[] buff = cipher.doFinal(Hex.decodeHex(data.toCharArray()));
         System.out.println(Arrays.toString(buff));
         return new String(buff);
     }

     /**
      * 解密<br>
      * 用公钥解密
      *
      * @param data
      * @return
      * @throws Exception
      */
     public static String decryptByPublicKey(String data)throws Exception {
         // 对密钥解密
         byte[] keyBytes = Base64.decodeBase64(getPublicKey());
         // 取得公钥
         X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         Key publicKey = keyFactory.generatePublic(x509KeySpec);
         //初始化Cipher对象，设置为解密模式
         Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
         cipher.init(Cipher.DECRYPT_MODE, publicKey);
         // 执行解密操作
         byte[] buff = cipher.doFinal(Hex.decodeHex(data.toCharArray()));
         System.out.println(Arrays.toString(buff));
         return new String(buff);
     }

     /**
      * 加密<br>
      * 用公钥加密
      *
      * @param data
      * @return
      * @throws Exception
      */
     public static String encryptByPublicKey(String data)throws Exception {
         // 对公钥解密
         byte[] keyBytes = Base64.decodeBase64(getPublicKey());
         // 取得公钥
         X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         Key publicKey = keyFactory.generatePublic(x509KeySpec);
         // 实例化Cipher对象，它用于完成实际的加密操作
         Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
         cipher.init(Cipher.ENCRYPT_MODE, publicKey);
         byte[] buff = cipher.doFinal(data.getBytes());
         System.out.println(Arrays.toString(buff));
         // 执行加密操作。加密后的结果通常都会用Base64编码进行传输
         return Hex.encodeHexString(buff);
     }

     /**
      * 加密<br>
      * 用私钥加密
      *
      * @param data
      * @return
      * @throws Exception
      */
     public static String encryptByPrivateKey(String data) throws Exception {
         // 对密钥解密
         byte[] keyBytes = Base64.decodeBase64(getPrivateKey());
         // 取得私钥
         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
         KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
         Key privateKey = keyFactory.generatePrivate(pkcs8KeySpec);
         // 对数据加密
         Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
         cipher.init(Cipher.ENCRYPT_MODE, privateKey);
         byte[] buff = cipher.doFinal(data.getBytes());
         System.out.println(Arrays.toString(buff));
         // 执行加密操作。加密后的结果通常都会用Base64编码进行传输
         return Hex.encodeHexString(buff);
     }

     /**
      * 取得私钥
      *
      * @param keyMap
      * @return
      * @throws Exception
      */
     public static String getPrivateKey()throws Exception{
         Key key = (Key)initKey().get(PRIVATE_KEY);
         return Base64.encodeBase64String(key.getEncoded());
     }

     /**
      * 取得公钥
      *
      * @param keyMap
      * @return
      * @throws Exception
      */
     public static String getPublicKey()throws Exception {
         Key key = (Key) initKey().get(PUBLIC_KEY);
         return Base64.encodeBase64String(key.getEncoded());
     }

     /**
      * 初始化密钥
      *
      * @return
      * @throws Exception
      * @throws Exception
      */
     public static Map<String, Object> initKey() throws Exception{
         InputStream in1 = RSAUtil.class.getClassLoader().getResourceAsStream(PUBLIC_KEY_PATH);
         InputStream in2 = RSAUtil.class.getClassLoader().getResourceAsStream(PRIVATE_KEY_PATH);
         try {
             KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
             /*生成公钥*/
             byte[] encodedpubkey = new byte[in1.available()];
             in1.read(encodedpubkey);
             X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encodedpubkey);
             PublicKey publicKey = keyFactory.generatePublic(pubKeySpec);
             /*生成私钥*/
             byte[] encodedprikey = new byte[in2.available()];
             in2.read(encodedprikey);
             PKCS8EncodedKeySpec priKeySpec = new PKCS8EncodedKeySpec(encodedprikey);
             PrivateKey privateKey = keyFactory.generatePrivate(priKeySpec);
             /*封装进map*/
             Map<String, Object> keyMap = new HashMap<String, Object>();
             keyMap.put(PUBLIC_KEY, publicKey);
             keyMap.put(PRIVATE_KEY, privateKey);
             return keyMap;
         } catch(Exception e){
             e.printStackTrace();
             throw e;
         } finally {
             in1.close();
             in2.close();
         }
     }
     /**
      * 初始化密钥 2
      * @return
      * @throws Exception
      */
     public static Map<String, Object> initKey2() throws Exception {
         KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(ALGORITHM);
         keyPairGen.initialize(1024);
         KeyPair keyPair = keyPairGen.generateKeyPair();
         // 公钥
         RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
         // 私钥
         RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
         Map<String, Object> keyMap = new HashMap<String, Object>(2);
         keyMap.put(PUBLIC_KEY, publicKey);
         keyMap.put(PRIVATE_KEY, privateKey);
         return keyMap;
     }

     public static void main(String[] args) throws Exception {
         String publicKey = getPublicKey();
         String privateKey = getPrivateKey();
         System.out.println("公钥:\r" + publicKey);
         System.out.println("私钥:\r" + privateKey);

         System.out.println("公钥加密————————————————————私钥解密");
         String data = "Somnus";
         System.out.println("原文: " + data);
         String encryptData = encryptByPublicKey(data);
         System.out.println("加密后: " + encryptData);
         String decryptData = decryptByPrivateKey(encryptData);
         System.out.println("解密后: " + decryptData);

         System.out.println("私钥加密————————————————————公钥解密");
         System.out.println("原文: " + data);
         String encryptData2 = encryptByPrivateKey(data);
         System.out.println("加密后: " + encryptData2);
         String decryptData2 = decryptByPublicKey(encryptData2);
         System.out.println("解密后: " + decryptData2);

         System.out.println("私钥签名——公钥验证签名");
         // 产生签名
         String sign = sign(encryptData2);
         System.out.println("签名:\r" + sign);
         // 验证签名
         boolean status = verify(encryptData2,sign);
         System.out.println("状态:" + status);
     }
 }

控制台输出： 

 公钥加密————————————————————私钥解密
 原文: Somnus
 [82, 112, 47, -49, -44, 28, 117, 87, -32, -5, -116, 56, -60, 87, -1, -36, 89, 84, -9, 17, -66, 64, -115, -114, 72, -86, 79, 63, -15, -35, -14, 40, -50, 16, -105, 73, 80, 7, -48, 75, -114, -64, 80, 74, 6, -74, 24, -59, -59, 31, 121, -63, 45, 93, 20, 25, -116, 51, -74, -40, 22, 55, -31, -106]
 加密后: 52702fcfd41c7557e0fb8c38c457ffdc5954f711be408d8e48aa4f3ff1ddf228ce1097495007d04b8ec0504a06b618c5c51f79c12d5d14198c33b6d81637e196
 [83, 111, 109, 110, 117, 115]
 解密后: Somnus
 私钥加密————————————————————公钥解密
 原文: Somnus
 [69, -38, -21, -84, -56, -1, 50, -33, -46, 11, 124, 37, -106, 53, 67, 81, -9, 39, -15, -89, 59, -49, 102, 71, 89, -7, 22, 42, 49, -29, 28, 114, -36, -1, -123, -7, 124, -104, -38, 83, 12, 76, 61, -117, 118, -54, 99, 99, 47, -118, 28, -119, 83, -5, 124, 122, -3, 109, 45, -38, -31, 98, 99, -107]
 加密后: 45daebacc8ff32dfd20b7c2596354351f727f1a73bcf664759f9162a31e31c72dcff85f97c98da530c4c3d8b76ca63632f8a1c8953fb7c7afd6d2ddae1626395
 [83, 111, 109, 110, 117, 115]
 解密后: Somnus
 私钥签名——公钥验证签名
 签名:
 GfLuZt88KdtRoTL7nJoeoRYGW0Lqu9eV4o9J8OVzH9jbHHGa/ZZDlCAjqS1jwkMYaXrut+W2a8v867mZDvQJtw==
 状态:true

    简要总结一下，使用公钥加密、私钥解密，完成了乙方到甲方的一次数据传递，通过私钥加密、公钥解密，同时通过私钥签名、公钥验证签名，完成了一次甲方到乙方的数据传递与验证，两次数据传递完成一整套的数据交互！

类似数字签名，数字信封是这样描述的： 

数字信封  
　　数字信封用加密技术来保证只有特定的收信人才能阅读信的内容。 
流程： 
    信息发送方采用对称密钥来加密信息，然后再用接收方的公钥来加密此对称密钥（这部分称为数字信封），再将它和信息一起发送给接收方；接收方先用相应的私钥打开数字信封，得到对称密钥，然后使用对称密钥再解开信息。