Java加密技术（六）——数字签名算法DSA

    接下来我们介绍DSA数字签名，非对称加密的另一种实现。 
DSA 
DSA-Digital Signature Algorithm 是Schnorr和ElGamal签名算法的变种，被美国NIST作为DSS(DigitalSignature Standard)。简单的说，这是一种更高级的验证方式，用作数字签名。不单单只有公钥、私钥，还有数字签名。私钥加密生成数字签名，公钥验证数据及签名。如果数据和签名不匹配则认为验证失败！数字签名的作用就是校验数据在传输过程中不被修改。数字签名，是单向加密的升级！  

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.PrivateKey;
 import java.security.PublicKey;
 import java.security.SecureRandom;
 import java.security.Signature;
 import java.security.interfaces.DSAPrivateKey;
 import java.security.interfaces.DSAPublicKey;
 import java.security.spec.PKCS8EncodedKeySpec;
 import java.security.spec.X509EncodedKeySpec;
 import java.util.HashMap;
 import java.util.Map;

 /**
  * DSA安全编码组件
  *
  * @author 梁栋
  * @version 1.0
  * @since 1.0
  */
 public abstract class DSACoder extends Coder {

     public static final String ALGORITHM = "DSA";

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

     /**
      * 默认种子
      */
     private static final String DEFAULT_SEED = "0f22507a10bbddd07d8a3082122966e3";

     private static final String PUBLIC_KEY = "DSAPublicKey";
     private static final String PRIVATE_KEY = "DSAPrivateKey";

     /**
      * 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(byte[] data, String privateKey) throws Exception {
         // 解密由base64编码的私钥
         byte[] keyBytes = decryptBASE64(privateKey);

         // 构造PKCS8EncodedKeySpec对象
         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);

         // KEY_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(keyFactory.getAlgorithm());
         signature.initSign(priKey);
         signature.update(data);

         return encryptBASE64(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(byte[] data, String publicKey, String sign)
             throws Exception {

         // 解密由base64编码的公钥
         byte[] keyBytes = decryptBASE64(publicKey);

         // 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(keyFactory.getAlgorithm());
         signature.initVerify(pubKey);
         signature.update(data);

         // 验证签名是否正常
         return signature.verify(decryptBASE64(sign));
     }

     /**
      * 生成密钥
      *
      * @param seed
      *            种子
      * @return 密钥对象
      * @throws Exception
      */
     public static Map<String, Object> initKey(String seed) throws Exception {
         KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);
         // 初始化随机产生器
         SecureRandom secureRandom = new SecureRandom();
         secureRandom.setSeed(seed.getBytes());
         keygen.initialize(KEY_SIZE, secureRandom);

         KeyPair keys = keygen.genKeyPair();

         DSAPublicKey publicKey = (DSAPublicKey) keys.getPublic();
         DSAPrivateKey privateKey = (DSAPrivateKey) keys.getPrivate();

         Map<String, Object> map = new HashMap<String, Object>(2);
         map.put(PUBLIC_KEY, publicKey);
         map.put(PRIVATE_KEY, privateKey);

         return map;
     }

     /**
      * 默认生成密钥
      *
      * @return 密钥对象
      * @throws Exception
      */
     public static Map<String, Object> initKey() throws Exception {
         return initKey(DEFAULT_SEED);
     }

     /**
      * 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 DSACoderTest {

     @Test
     public void test() throws Exception {
         String inputStr = "abc";
         byte[] data = inputStr.getBytes();

         // 构建密钥
         Map<String, Object> keyMap = DSACoder.initKey();

         // 获得密钥
         String publicKey = DSACoder.getPublicKey(keyMap);
         String privateKey = DSACoder.getPrivateKey(keyMap);

         System.err.println("公钥:\r" + publicKey);
         System.err.println("私钥:\r" + privateKey);

         // 产生签名
         String sign = DSACoder.sign(data, privateKey);
         System.err.println("签名:\r" + sign);

         // 验证签名
         boolean status = DSACoder.verify(data, publicKey, sign);
         System.err.println("状态:\r" + status);
         assertTrue(status);

     }

 }

控制台输出： 

 公钥:
 MIIBtzCCASwGByqGSM44BAEwggEfAoGBAP1/U4EddRIpUt9KnC7s5Of2EbdSPO9EAMMeP4C2USZp
 RV1AIlH7WT2NWPq/xfW6MPbLm1Vs14E7gB00b/JmYLdrmVClpJ+f6AR7ECLCT7up1/63xhv4O1fn
 xqimFQ8E+4P208UewwI1VBNaFpEy9nXzrith1yrv8iIDGZ3RSAHHAhUAl2BQjxUjC8yykrmCouuE
 C/BYHPUCgYEA9+GghdabPd7LvKtcNrhXuXmUr7v6OuqC+VdMCz0HgmdRWVeOutRZT+ZxBxCBgLRJ
 FnEj6EwoFhO3zwkyjMim4TwWeotUfI0o4KOuHiuzpnWRbqN/C/ohNWLx+2J6ASQ7zKTxvqhRkImo
 g9/hWuWfBpKLZl6Ae1UlZAFMO/7PSSoDgYQAAoGAIu4RUlcQLp49PI0MrbssOY+3uySVnp0TULSv
 5T4VaHoKzsLHgGTrwOvsGA+V3yCNl2WDu3D84bSLF7liTWgOj+SMOEaPk4VyRTlLXZWGPsf1Mfd9
 21XAbMeVyKDSHHVGbMjBScajf3bXooYQMlyoHiOt/WrCo+mv7efstMM0PGo=

 私钥:
 MIIBTAIBADCCASwGByqGSM44BAEwggEfAoGBAP1/U4EddRIpUt9KnC7s5Of2EbdSPO9EAMMeP4C2
 USZpRV1AIlH7WT2NWPq/xfW6MPbLm1Vs14E7gB00b/JmYLdrmVClpJ+f6AR7ECLCT7up1/63xhv4
 O1fnxqimFQ8E+4P208UewwI1VBNaFpEy9nXzrith1yrv8iIDGZ3RSAHHAhUAl2BQjxUjC8yykrmC
 ouuEC/BYHPUCgYEA9+GghdabPd7LvKtcNrhXuXmUr7v6OuqC+VdMCz0HgmdRWVeOutRZT+ZxBxCB
 gLRJFnEj6EwoFhO3zwkyjMim4TwWeotUfI0o4KOuHiuzpnWRbqN/C/ohNWLx+2J6ASQ7zKTxvqhR
 kImog9/hWuWfBpKLZl6Ae1UlZAFMO/7PSSoEFwIVAIegLUtmm2oQKQJTOiLugHTSjl/q

 签名:
 MC0CFQCMg0J/uZmF8GuRpr3TNq48w60nDwIUJCyYNah+HtbU6NcQfy8Ac6LeLQs=

 状态:
 true

注意状态为true，就验证成功！