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 Client {

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

        String host = args[0];
        int port = Integer.parseInt(args[1]);
        String userId = args[2];

        // Connect to server
        Socket s = new Socket(host, port);
        DataInputStream din = new DataInputStream(s.getInputStream());
        DataOutputStream dout = new DataOutputStream(s.getOutputStream());
        ObjectInputStream oin = new ObjectInputStream(s.getInputStream());
        ObjectOutputStream oout = new ObjectOutputStream(s.getOutputStream());

        dout.writeUTF(userId);
        SecretKey desedeKey = keyAgreement(oin, oout,userId,din,dout);

        byte [] encryptedoutput = new byte[din.readInt()];
        din.readFully(encryptedoutput);

        Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, desedeKey);
         String fileval = new  String(cipher.doFinal(encryptedoutput));

        System.out.println(fileval);

    }




    // Stage 2: manual DH
    private static SecretKey keyAgreement(ObjectInputStream oin, ObjectOutputStream oout,String userId,DataInputStream in,DataOutputStream out) throws Exception {

        String skip1024String =
                "F488FD584E49DBCD20B49DE49107366B336C380D451D0F7C88B31C7C5B2D8EF6"+
                        "F3C923C043F0A55B188D8EBB558CB85D38D334FD7C175743A31D186CDE33212C"+
                        "B52AFF3CE1B1294018118D7C84A70A72D686C40319C807297ACA950CD9969FAB"+
                        "D00A509B0246D3083D66A45D419F9C7CBD894B221926BAABA25EC355E92F78C7";

        BigInteger base = BigInteger.valueOf(2);
        BigInteger modulus = new BigInteger(skip1024String, 16);

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

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

        BigInteger key = ea.modPow(b, modulus);

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

        SecretKey finalkey =  desedeFactory.generateSecret(spec);

        ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(userId+".prv"));
        PrivateKey privateKey = (PrivateKey) keyIn.readObject();
        keyIn.close();

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

        Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, finalkey);
        byte[] output = cipher.doFinal(signature);
        out.writeInt(output.length);
        out.write(output);

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

        Cipher dcipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
        dcipher.init(Cipher.DECRYPT_MODE, finalkey);
        byte [] signatureServer = dcipher.doFinal(encryptedServerSignature);

        ObjectInputStream keyInServer = new ObjectInputStream(new FileInputStream("server.pub"));
        PublicKey publicKey = (PublicKey) keyInServer.readObject();
        keyInServer.close();

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

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

        return finalkey;
    }

}