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.spec.PKCS8EncodedKeySpec;  
import java.security.spec.X509EncodedKeySpec;  
import java.util.HashMap;  
import java.util.Map;  
  
import sun.misc.BASE64Decoder;  
import sun.misc.BASE64Encoder;  
  
/** 
 * 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！即 传输中的数据 可以不再加密，接收方获得数据后，拿到公钥与签名 验证数据是否有效 
 *  
 * @author stone 
 * @date 2014-03-11 09:50:51 
 */  
public class DSA {  
    //不仅可以使用DSA算法，同样也可以使用RSA算法做数字签名  
    /*public static final String KEY_ALGORITHM = "RSA"; 
    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";*/  
      
    public static final String KEY_ALGORITHM = "DSA";  
    public static final String SIGNATURE_ALGORITHM = "DSA";  
      
    public static final String DEFAULT_SEED = "$%^*%^()(HJG8awfjas7"; //默认种子  
    public static final String PUBLIC_KEY = "DSAPublicKey";  
    public static final String PRIVATE_KEY = "DSAPrivateKey";  
      
    public static void main(String[] args) throws Exception {  
        String str = "!@#$!#^$#&ZXVDF呆军工路爱着你*()_+";  
        byte[] data = str.getBytes();  
          
        Map<String, Object> keyMap = initKey();// 构建密钥  
        PublicKey publicKey = (PublicKey) keyMap.get(PUBLIC_KEY);  
        PrivateKey privateKey = (PrivateKey) keyMap.get(PRIVATE_KEY);  
        System.out.println("私钥format：" + privateKey.getFormat());  
        System.out.println("公钥format：" + publicKey.getFormat());  
          
          
        // 产生签名  
        String sign = sign(data, getPrivateKey(keyMap));  
          
        // 验证签名   
        boolean verify1 = verify("aaa".getBytes(), getPublicKey(keyMap), sign);  
        System.err.println("经验证 数据和签名匹配:" + verify1);     
          
        boolean verify = verify(data, getPublicKey(keyMap), sign);  
        System.err.println("经验证 数据和签名匹配:" + verify);     
    }  
      
    /**   
     * 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 {  
        System.out.println("生成密钥");  
          
        KeyPairGenerator keygen = KeyPairGenerator.getInstance(KEY_ALGORITHM);  
        SecureRandom secureRandom = new SecureRandom();     
        secureRandom.setSeed(seed.getBytes());   
        //Modulus size must range from 512 to 1024 and be a multiple of 64  
        keygen.initialize(640, secureRandom);    
          
        KeyPair keys = keygen.genKeyPair();  
        PrivateKey privateKey = keys.getPrivate();  
        PublicKey publicKey = keys.getPublic();  
          
        Map<String, Object> map = new HashMap<String, Object>(2);  
        map.put(PUBLIC_KEY, publicKey);     
        map.put(PRIVATE_KEY, privateKey);  
        return map;  
    }  
      
    /**   
     * 生成默认密钥   
     *    
     * @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()); //base64加密私钥  
    }     
    
    /**   
     * 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()); //base64加密公钥  
    }     
      
    /** 
     *  用私钥对信息进行数字签名 
     * @param data  加密数据 
     * @param privateKey 私钥-base64加密的 
     * @return  
     * @throws Exception 
     */  
    public static String sign(byte[] data, String privateKey) throws Exception {  
        System.out.println("用私钥对信息进行数字签名");  
          
        byte[] keyBytes = decryptBASE64(privateKey);  
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);  
        KeyFactory factory = KeyFactory.getInstance(KEY_ALGORITHM);  
        PrivateKey priKey = factory.generatePrivate(keySpec);//生成 私钥  
          
        //用私钥对信息进行数字签名  
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);  
        signature.initSign(priKey);  
        signature.update(data);  
        return encryptBASE64(signature.sign());  
    }  
      
    /** 
     * BASE64Encoder 加密 
     * @param data 要加密的数据 
     * @return 加密后的字符串 
     */  
    private static String encryptBASE64(byte[] data) {  
        BASE64Encoder encoder = new BASE64Encoder();  
        String encode = encoder.encode(data);  
        return encode;  
    }  
      
    /** 
     * BASE64Decoder 解密 
     * @param data 要解密的字符串 
     * @return 解密后的byte[] 
     * @throws Exception  
     */  
    private static byte[] decryptBASE64(String data) throws Exception {  
        BASE64Decoder decoder = new BASE64Decoder();  
        byte[] buffer = decoder.decodeBuffer(data);  
        return buffer;  
    }  
      
    /** 
     * 校验数字签名 
     * @param data 加密数据 
     * @param publicKey 
     * @param sign 数字签名 
     * @return 
     * @throws Exception 
     */  
    public static boolean verify(byte[] data, String publicKey, String sign) throws Exception {  
        byte[] keyBytes = decryptBASE64(publicKey);   
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);  
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);    
        PublicKey pubKey = keyFactory.generatePublic(keySpec);  
          
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);     
        signature.initVerify(pubKey);   
        signature.update(data);  
          
        return signature.verify(decryptBASE64(sign)); //验证签名  
    }  
      
}