SigTest.java

[SigTest.java]

import client.Client;
import server.Server;

import java.security.KeyPair;
import java.security.PrivateKey;
import java.security.PublicKey;

public class SigTest {
    public static void main(String[] args) throws Exception {
        String text = "This is plain text!";

        KeyPair kp = Client.ReadKey();
        PrivateKey privateKey = kp.getPrivate();
        PublicKey publicKey = kp.getPublic();
        byte[] signature = Client.Sign(text, privateKey);

        Server.Verify(text, signature, publicKey);
    }
}

[Client.java]

package client;

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import javax.xml.bind.DatatypeConverter;

import java.security.Security;
import java.security.Signature;
import java.security.KeyPair;
import java.security.PrivateKey;

import java.security.SignatureException;
import java.security.NoSuchAlgorithmException;
import java.security.InvalidKeyException;

import org.bouncycastle.openssl.PEMKeyPair;
import org.bouncycastle.openssl.PEMParser;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

public class Client {
    public static byte[] Sign(String text, PrivateKey privateKey) throws NoSuchAlgorithmException, InvalidKeyException, UnsupportedEncodingException, SignatureException {
        Signature dsa = Signature.getInstance("SHA256withECDSA");
        dsa.initSign(privateKey);
        dsa.update(text.getBytes("UTF-8"));
        byte[] signature = dsa.sign();
        System.out.println("Signature: " + DatatypeConverter.printHexBinary(signature));

        return signature;
    }

    public static KeyPair ReadKey() throws IOException {
        String filename = "./key/secret.key";
//        String filename = "./key/private_prime256v1.key";
        PEMParser pemParser = new PEMParser(new FileReader(new File(filename)));
        PEMKeyPair params = (PEMKeyPair) pemParser.readObject();
        KeyPair kp = new JcaPEMKeyConverter().getKeyPair(params);

        return kp;
    }
}

[Server.java]

package server;

import java.io.UnsupportedEncodingException;

import java.security.Signature;
import java.security.PublicKey;

import java.security.NoSuchAlgorithmException;
import java.security.InvalidKeyException;
import java.security.SignatureException;

public class Server {
    public static void Verify(String text, byte[] signature, PublicKey publicKey) throws NoSuchAlgorithmException, InvalidKeyException, UnsupportedEncodingException, SignatureException {
        Signature dsa = Signature.getInstance("SHA256withECDSA");
        dsa.initVerify(publicKey);
        dsa.update(text.getBytes("UTF-8"));
        boolean verifyResult = dsa.verify(signature);
        System.out.println("Verify: " + verifyResult);
    }
}