import java.io.*;
import java.net.*;
import java.util.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.math.BigInteger;
import java.nio.ByteBuffer;

public class Server {

    static ArrayList<Double> pastRand;

    public static void main(String args[]) throws Exception {

        // Listen for connections
        int port = Integer.parseInt(args[0]);
        ServerSocket ss = new ServerSocket(port);

        // infinite loop
        while(true) {

            try {

                Socket s = ss.accept();
                DataInputStream din = new DataInputStream(s.getInputStream());
                DataOutputStream dout = new DataOutputStream(s.getOutputStream());
                ObjectOutputStream oout = new ObjectOutputStream(s.getOutputStream());
                ObjectInputStream oin = new ObjectInputStream(s.getInputStream());

                String userid = din.readUTF();

                SecretKey desedeKey = keyAgreement(oin, oout,userid,dout,din);

                BufferedReader br = new BufferedReader(new FileReader(userid));
                String message = br.readLine();

                Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
                cipher.init(Cipher.ENCRYPT_MODE, desedeKey);
                byte[] output = cipher.doFinal(message.getBytes("UTF8"));
                dout.writeInt(output.length);
                dout.write(output);


            }
            catch (EOFException e) {
                System.err.println("client disconnected.");
                continue;
            }
        }
    }





    // Stage 2: manual DH

    private static SecretKey keyAgreement(ObjectInputStream oin, ObjectOutputStream oout,String userId,DataOutputStream dout,DataInputStream in) throws Exception {

        String skip1024String =
                "F488FD584E49DBCD20B49DE49107366B336C380D451D0F7C88B31C7C5B2D8EF6"+
                        "F3C923C043F0A55B188D8EBB558CB85D38D334FD7C175743A31D186CDE33212C"+
                        "B52AFF3CE1B1294018118D7C84A70A72D686C40319C807297ACA950CD9969FAB"+
                        "D00A509B0246D3083D66A45D419F9C7CBD894B221926BAABA25EC355E92F78C7";
        BigInteger base = BigInteger.valueOf(2);
        BigInteger modulus = new BigInteger(skip1024String, 16);

        BigInteger a;
        do {
            a = new BigInteger(1024, new Random());
        }while(a.bitLength() < 1024);

        BigInteger ea = base.modPow(a, modulus);
        oout.writeObject(ea);
        BigInteger eb = (BigInteger)oin.readObject();
        BigInteger key = eb.modPow(a, modulus);

        byte[] keyBytes = key.toByteArray();
        SecretKeyFactory desedeFactory = SecretKeyFactory.getInstance("DESede");
        KeySpec spec = new DESedeKeySpec(keyBytes);

        SecretKey finalkey =  desedeFactory.generateSecret(spec);

        byte [] encryptedsignature = new byte[in.readInt()];
        in.readFully(encryptedsignature);

        Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, finalkey);
        byte [] signature = cipher.doFinal(encryptedsignature);

        ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(userId+".pub"));
        PublicKey publicKey = (PublicKey) keyIn.readObject();
        keyIn.close();

        Signature sig = Signature.getInstance("DSA");
        sig.initVerify(publicKey);
        sig.update(eb.toByteArray());
        sig.update(ea.toByteArray());

        if (sig.verify(signature))
            System.out.println("Client logged in");
        else {
            System.out.println("Client failed to log in");
            System.exit(-1);
        }


        ObjectInputStream keyInServer = new ObjectInputStream(new FileInputStream("server.prv"));
        PrivateKey privateKey = (PrivateKey) keyInServer.readObject();
        keyInServer.close();

        Signature sigServer = Signature.getInstance("DSA");
        sigServer.initSign(privateKey);
        sigServer.update(ea.toByteArray());
        sigServer.update(eb.toByteArray());
        byte[] signatureServer = sigServer.sign();

        Cipher ecipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
        ecipher.init(Cipher.ENCRYPT_MODE, finalkey);
        byte[] output = ecipher.doFinal(signatureServer);
        dout.writeInt(output.length);
        dout.write(output);
        return finalkey;
    }





}