其實DSA的實現和RSA差不多，只是改了改介面名稱。

注意，我的程式碼只是用jdk實現，並沒有用BC，想學的人可以自己深究一下。

程式碼：

package 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;

public class DSA {
	
	//jdk只提供了SHA1withDSA,其他的用BC實現
	
	private static String dsa = "CYK";
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		jdkDSA();
	}
	
	public static void jdkDSA() {
		//1.初始化祕鑰
		KeyPairGenerator keyPairGenerator;
		try {
			keyPairGenerator = KeyPairGenerator.getInstance("DSA");
			keyPairGenerator.initialize(512);
			KeyPair keyPair = keyPairGenerator.generateKeyPair();
			DSAPublicKey dsaPublicKey = (DSAPublicKey)keyPair.getPublic();
			DSAPrivateKey dsaPrivateKey = (DSAPrivateKey)keyPair.getPrivate();
			
			//執行簽名
			PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(dsaPrivateKey.getEncoded());
			KeyFactory keyFactory = KeyFactory.getInstance("DSA");
			//這一步注意更改一下catch，讓它獲取所有錯誤
			PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
			//宣告簽名的物件
			Signature signature = Signature.getInstance("SHA1withDSA");
			signature.initSign(privateKey);
			signature.update(dsa.getBytes());
			byte[] result = signature.sign();
			System.out.println("jdk dsa sign:" + result);
			
			//3.驗證簽名
			X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(dsaPublicKey.getEncoded());
			keyFactory = KeyFactory.getInstance("DSA");
			PublicKey publicKey = keyFactory.generatePublic(x509EncodedKeySpec);
			signature = Signature.getInstance("SHA1withDSA");
			signature.initVerify(publicKey);
			signature.update(dsa.getBytes());
			boolean bool = signature.verify(result);
			System.out.println("jdk dsa verify:" + bool);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}