server.java

package DiffieHellman;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Inet4Address;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;


public class server implements host 
{
  private static final int DEFAULT_PORT = 12323;
  private ServerSocket serverSocket;  
  private Socket socket;
  
  /**
    *Open a new connection on the default port.
    */
  public server() throws IOException 
  {
    new server(DEFAULT_PORT);
  }

  /**
    *Open a new connection on the specified port.
    */
  public server(int port) throws IOException 
  {
    serverSocket = new ServerSocket(port);
  }

  /**
    *Run the server.
    */
  public void run() throws IOException 
  {
    while (true) 
    { 
      acceptConnection();
      int privateKey = getPrivateKey();
      String cipher = readMessage();
      String decryption = decryptMessage(cipher, privateKey);
      printMessages(cipher, decryption);
      socket.close();
    }
  }

  /**
    *Wait for a connection to the server socket from the client and accept it.
    */
  private void acceptConnection() throws IOException 
  {
    System.out.println(getInetAddress() + " Listening on port " + 
    serverSocket.getLocalPort() + "...");
    
    this.socket = serverSocket.accept();
    
    System.out.println("Accepted connection from " + 
    socket.getRemoteSocketAddress());
  }
  
  private int getPrivateKey() throws IOException 
  {
    diffieHellmanKeyDelivery creator = 
    new diffieHellmanKeyDelivery(this, false);
    return creator.calculateKey();
  }
  
  /**
    *Get the local IPv4 address.
    */
  private String getInetAddress() 
  {
    try 
    {
      return Inet4Address.getLocalHost().getHostAddress();
    } catch (UnknownHostException e) 
    {
      return "";
    }
  }
  
  /**
    *Read the input from the client and prints the data in UTF format.
    */
  public String readMessage() throws IOException 
  {
    DataInputStream inputStream = new DataInputStream(socket.getInputStream());
    return inputStream.readUTF();
  }
  
  /**
    *Decrypts the cipher sent by the client. 
    */
  private String decryptMessage(String cipher, int privateKey) 
  {
    encryption scheme = new encryption(privateKey);
    return scheme.decrypt(cipher);
  }
  
  /**
    *Print the encrypted and decrypted messages.
    */
  private void printMessages(String cipher, String decryption) 
  {
    System.out.println("\nReceived encrypted message:\n" + cipher + "\n");
    System.out.println("Decrypted:\n" + decryption + "\n");
  }
  
  /**
    *Sends a message to the client.
    */
  public void sendMessage(String message) throws IOException 
  {
    DataOutputStream outputStream = 
    new DataOutputStream(socket.getOutputStream());
    outputStream.writeUTF(message);
  }
  
  /**
    *Retrieve the port from the args array.
    */
  private static int getPortFromArgs(String[] args) 
  {
    if (args.length > 0) 
    {
      try 
      {
        return Integer.parseInt(args[0]);
      } catch (NumberFormatException e) 
      {
        return DEFAULT_PORT;
      }
    }
    return DEFAULT_PORT;
  }
  
  public static void main(String[] args) 
  {
    int port = getPortFromArgs(args);
    try 
    {
      server s = new server(port);
      s.run();
    } catch (IOException e) 
    {
      e.printStackTrace();
    }
  }
}