package digital_signature;

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.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

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

public class JavaDSA {

	private static String src = "Can I help you?";
	
	public static void main(String[] args) throws Exception {
		jdkDSA();
	}

	public static void jdkDSA() throws Exception{
		
		//1.初始化密钥
		KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DSA");
		keyPairGenerator.initialize(512);
		KeyPair keyPair = keyPairGenerator.generateKeyPair();
		DSAPublicKey dsaPublicKey = (DSAPublicKey) keyPair.getPublic();
		DSAPrivateKey dsaPrivateKey = (DSAPrivateKey) keyPair.getPrivate();
		
		//2.执行签名【私钥签名】
		PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(dsaPrivateKey.getEncoded());
		KeyFactory keyFactory = KeyFactory.getInstance("DSA");
		PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
		Signature signature = Signature.getInstance("SHA1WithDSA");
		signature.initSign(privateKey);
		signature.update(src.getBytes());
		byte[] result = signature.sign();
		System.out.println("JDK实现DSA数字签名:" + Hex.encodeHexString(result));
		
		//3.验证签名【公钥验证】
		X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(dsaPublicKey.getEncoded());
		keyFactory = KeyFactory.getInstance("DSA");
		PublicKey publicKey = keyFactory.generatePublic(x509EncodedKeySpec);
		signature = Signature.getInstance("SHA1WithDSA");
		signature.initVerify(publicKey);
		signature.update(src.getBytes());
		boolean bool = signature.verify(result);
		System.out.println("数字签名有效?" + bool);
	}
}