Receives a RSA asymmetric public key from the Client, generates a AES symmetric key - Java Network

Java examples for Network:Socket

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Introduction

  • Receives a RSA asymmetric public key from the Client
  • generates a AES symmetric key
  • encrypts the AES symmetric key with the RSA asymmetric public key
  • sends the encrypted data to the Client

Demo Code


import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import sun.misc.IOUtils;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PublicKey;
import java.security.SecureRandom;

public class SecureServer {

    private static final Logger logger = LogManager.getLogger(SecureServer.class);

    public static void main(String[] args) throws NoSuchPaddingException, NoSuchAlgorithmException, NoSuchProviderException {
        if (args.length != 1) {
            System.err.println("Usage: java SecureServer <port number>");
            System.exit(1);//from www. j av  a2s  . c  om
        }

        int portNumber = Integer.parseInt(args[0]);
        byte[] message = null;

        logger.trace("Sever started");

        try {
            ServerSocket serverSocket =
                    new ServerSocket(Integer.parseInt(args[0]));
            Socket clientSocket = serverSocket.accept();
            ObjectInputStream in = new ObjectInputStream(
                    clientSocket.getInputStream());

            // receives RSA asymmetric public key from Client
            PublicKey publicKey = (PublicKey) in.readObject();

            // generates AES symmetric key
            KeyGenerator keyGen = KeyGenerator.getInstance("AES");
            keyGen.init(128);
            SecretKey secretKey = keyGen.generateKey();

            logger.trace("generated AES symmetric key: " + secretKey.toString());
            logger.trace("received public key: " + publicKey.toString());


            // uses asymmetric public RSA key from client to encrypt symmetric AES key
            Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
            cipher.init(Cipher.ENCRYPT_MODE, publicKey);
            byte[] encryptedData = cipher.doFinal(secretKey.getEncoded());

            OutputStream outputStream = clientSocket.getOutputStream();
            DataOutputStream dataOutputStream = new DataOutputStream(outputStream);
            dataOutputStream.writeInt(encryptedData.length);
            dataOutputStream.write(encryptedData, 0, encryptedData.length);
            logger.trace("sent AES symmetric key");


            // read IV
            DataInputStream dataInputStream = new DataInputStream(
                    clientSocket.getInputStream());
            byte[] iv = new byte[16];
            dataInputStream.read(iv);
            IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

            // read encrypted message
            int length = dataInputStream.readInt(); // read length of incoming message
            if (length > 0) {
                message = new byte[length];
                dataInputStream.readFully(message, 0, message.length); // read the message
            }
            logger.info("received encrypted message: " + encryptedData);

            // use AES key for decrypting the message
            cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipher.init(Cipher.DECRYPT_MODE, secretKey, ivParameterSpec);
            String decrypted = new String(cipher.doFinal(message), "UTF-8");
            logger.info("decrypted message: " + decrypted );

        } catch (Exception e ){
            e.printStackTrace();
        }
    }
}

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