Sending the key with Socket

Question

Hello!
I have made an application that encrypts a byte[], sends it to a server.
And after that i am trying to decrypt it. But that gives me problem.
The exception i get is:
BadPaddingException: javax.crypto.BadPaddingException: Given final block not properly padded.
This is my code.
The client
import java.net.*;
import java.io.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.security.*;
import java.security.spec.*;
import java.util.*;
class Client
  public static void main(String a[])
    Socket socket = null;
    try
      // Create Key
      KeyGenerator kg = KeyGenerator.getInstance("DES");
      SecretKey secretKey = kg.generateKey();
      // Create Cipher
      Cipher desCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
      desCipher.init(Cipher.ENCRYPT_MODE, secretKey);
      socket = new Socket("localhost", 3000);
      DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
      ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
      File file = new File("Mattias.jpg");
      FileInputStream fileInputStream = new FileInputStream(file);
      byte[] bytes = new byte[(int)file.length()];
      fileInputStream.read(bytes);
      fileInputStream.close();
      byte[] encryptedBytes = new byte[(int)file.length()];
      encryptedBytes = desCipher.doFinal(bytes);
      out.writeInt((int)file.length());
      out.writeObject((Object)secretKey);
      dataOutputStream.write(encryptedBytes);
      out.flush();
      dataOutputStream.flush();
      out.close();
      dataOutputStream.close();
    catch(IOException e)
      e.printStackTrace();
    catch (NoSuchPaddingException e)
      System.err.println("Padding problem: " + e);
    catch (NoSuchAlgorithmException e)
      System.err.println("Invalid algorithm: " + e);
    catch (InvalidKeyException e)
      System.err.println("Invalid key: " + e);
    catch (IllegalBlockSizeException e)
      System.err.println("IllegalBlockSizeException: " + e);
    catch (BadPaddingException e)
      System.err.println("BadPaddingException: " + e);
    finally
      try
        socket.close();
      catch(IOException e)
        e.printStackTrace();   
The server
import java.net.*;
import java.io.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.security.*;
import java.security.spec.*;
import java.util.*;
class Server
  public static void main(String a[]) throws IOException
    new Server().listen(3000);
  public void listen(int port) throws IOException
    ServerSocket serverSocket = new ServerSocket(port);
    new SocketHandler(serverSocket.accept()).start();
  class SocketHandler extends Thread
    Socket socket = null;
    SocketHandler(Socket socket)
      this.socket = socket;
    public void run()
      try
        SecretKey secretKey = null;
        File file = new File("file.jpg");
        OutputStream fileOutputStream = new FileOutputStream(file);
        BufferedInputStream bufferedInputStream = new BufferedInputStream(socket.getInputStream());
        ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
        int fileSize = in.readInt();
        byte[] encryptedBytes = new byte[fileSize * 8];
        byte[] bytes = new byte[fileSize];
        secretKey = (SecretKey)in.readObject();
        // Create Cipher
        Cipher desCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
        desCipher.init(Cipher.DECRYPT_MODE, secretKey);
        int i = -1;
        while (true)
          i = bufferedInputStream.read(encryptedBytes, 0, encryptedBytes.length);
          bytes = desCipher.doFinal(encryptedBytes);
          if (i == -1)
            break;
          fileOutputStream.write(bytes, 0, i);
        bufferedInputStream.close();
        fileOutputStream.flush();
        fileOutputStream.close();
      catch (IOException ioe)
        ioe.printStackTrace();
        catch(ClassNotFoundException cnfe)
        cnfe.printStackTrace();
      catch (NoSuchPaddingException e)
        System.err.println("Padding problem: " + e);
      catch (NoSuchAlgorithmException e)
        System.err.println("Invalid algorithm: " + e);
      catch (InvalidKeyException e)
        System.err.println("Invalid key: " + e);
      catch (IllegalBlockSizeException e)
        System.err.println("IllegalBlockSizeException: " + e);
      catch (BadPaddingException e)
        System.err.println("BadPaddingException: " + e);
      finally
        try
          socket.close();
        catch (IOException ioe)
          ioe.printStackTrace();
}What am i doing wrong? How should i solve it?

Answer 1

This looks suspect -DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
      ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());It is normally a bad idea to attach a single OutputStream to 2 or more 'filter' streams.
You could always sent the data as an object i.e.out.writeObject(encryptedBytes);Also, you make the assumption that the encrypted length is the same as the file length. With PKCS5Padding this is never the case since it pads with 1 to 8 bytes to make up to the block size. This is probably the cause of the BadPaddingException. If you send the encrpted data over as an object then you don't need to send the length.
Your stream uses in the client and server differ. You have no DataInputStream in the server to match the DataOuputStream in the client. To be safe, stick to Object streams or Data streams but don't mix.
P.S. Isn't sending the key with the cipher text a litte insecure!!!