數字簽名算法DSA

DSA數字簽名，非對稱加密的另外一種實現。
DSA
DSA-Digital Signature Algorithm 是Schnorr和ElGamal簽名算法的變種，被美國NIST做爲DSS(DigitalSignature Standard)。簡單的說，這是一種更高級的驗證方式，用做數字簽名。不僅僅只有公鑰、私鑰，還有數字簽名。私鑰加密生成數字簽名，公鑰驗證數據及籤 名。若是數據和簽名不匹配則認爲驗證失敗！數字簽名的做用就是校驗數據在傳輸過程當中不被修改。數字簽名，是單向加密的升級！

經過java代碼實現以下：

package com.java.security;
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安全編碼組件
 * 
 */
public class DSAUtil extends EncryptUtils {

    public static final String ALGORITHM = "DSA";

    /**
     * 默認密鑰字節數
     */
    private static final int KEY_SIZE = 1024;

    /**
     * 默認種子
     */
    private static final String DEFAULT_SEED = "0f22507a10bbddd07d8a3082122966e3";
    private static final String PUBLIC_KEY = "DSAPublicKey";
    private static final String PRIVATE_KEY = "DSAPrivateKey";

    /**
     * 用私鑰對信息生成數字簽名
     * 
     * @param data  加密數據
     * @param privateKey 私鑰
     * 
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, String privateKey) throws Exception {
        // 解密由base64編碼的私鑰
        byte[] keyBytes = decryptBASE64(privateKey);

        // 構造PKCS8EncodedKeySpec對象
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);

        // KEY_ALGORITHM 指定的加密算法
        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);

        // 取私鑰匙對象
        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);

        // 用私鑰對信息生成數字簽名
        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());
        signature.initSign(priKey);
        signature.update(data);

        return encryptBASE64(signature.sign());
    }

    /**
     * 校驗數字簽名
     * 
     * @param data   加密數據
     * @param publicKey 公鑰
     * @param sign  數字簽名
     * @return 校驗成功返回true 失敗返回false
     * @throws Exception
     * 
     */
    public static boolean verify(byte[] data, String publicKey, String sign) throws Exception {

        // 解密由base64編碼的公鑰
        byte[] keyBytes = decryptBASE64(publicKey);
        // 構造X509EncodedKeySpec對象
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);

        // ALGORITHM 指定的加密算法
        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);

        // 取公鑰匙對象
        PublicKey pubKey = keyFactory.generatePublic(keySpec);

        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());
        signature.initVerify(pubKey);
        signature.update(data);

        // 驗證簽名是否正常
        return signature.verify(decryptBASE64(sign));
    }

    /**
     * 生成密鑰
     * 
     * @param seed
     *            種子
     * @return 密鑰對象
     * @throws Exception
     */
    public static Map<String, Object> initKey(String seed) throws Exception {
        KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);
        // 初始化隨機產生器
        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;
    }

    /**
     * 默認生成密鑰
     * 
     * @return 密鑰對象
     * @throws Exception
     */
    public static Map<String, Object> initKey() throws Exception {
        return initKey(DEFAULT_SEED);
    }

    /**
     * 取得私鑰
     * @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());
    }

    /**
     * 取得公鑰
     * @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());
    }
    
    public static void main(String[] args) throws Exception{
        String inputStr = "abc";  
        byte[] data = inputStr.getBytes();  
  
        // 構建密鑰  
        Map<String, Object> keyMap = initKey();  
        // 得到密鑰  
        String publicKey = getPublicKey(keyMap);  
        String privateKey = getPrivateKey(keyMap);  
  
        System.err.println("公鑰:\r" + publicKey);  
        System.err.println("私鑰:\r" + privateKey);  
  
        // 產生簽名  
        String sign = sign(data, privateKey);  
        System.err.println("簽名:\r" + sign);  
  
        // 驗證簽名  
        boolean status = verify(data, publicKey, sign);  
        System.err.println("狀態:\r" + status);  
    }
}