// Sample use of Java classes MessageDigest and SecureRandom.  See the Java
// API for more information.  Recall, MessageDigest supplies hash objects and
// SecureRandom supplies a crytographically strong random number (a large
// number with a high probability of being prime).
import java.io.*;
import java.math.BigInteger;
import java.net.*;

public class DH_Server {
   public static void main (String arg[]) {
      InputStreamReader isr;
      BufferedReader in;
      PrintWriter out;

      try {
	 DiffieHellmanExchange dh = new DiffieHellmanExchange("DHKey");
	 
	 // Wait for a connection from a client then connect
	 ServerSocket socket = new ServerSocket(8284);
	 Socket connect = socket.accept();
	 isr = new InputStreamReader(connect.getInputStream());
	 in = new BufferedReader(isr);
	 out = new PrintWriter (connect.getOutputStream(), true);
	    
	 // Receive public key from the client
	 BigInteger pkey = new BigInteger(in.readLine());
	 System.out.println("Server: client's public key = "+pkey.toString());
	 dh.s_secret = pkey.modPow(dh.x, dh.key.p);	 
	 out.println(dh.x_pub.toString());
	 System.out.println("Server: server's public key = "+dh.x_pub.toString());
	 System.out.println("Server: secret = "+dh.s_secret);

	 // Leave
	 in.close();
	 out.close();
	 socket.close();
      } catch (Exception e) {
	 System.out.println("Whoops! - no network");
      }
   }
}