Hallo,
I did AES crypt for my UDP chat, but it write this error: javax.crypto.BadPaddingException: Given final block not properly padded. On line with: 
byte dekodovani[]=cipher.doFinal(encrypt);
.Thanks for your advice.
package aes;
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;
 
/**
 *
 * @author Lolek
 */
public class Main {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        try {
 
            String hostname;
            if (args.length==0)
            {
                hostname = "127.0.0.1";
            }
            else
            { 
                hostname = args[0];
            }
 
            InetAddress ia = InetAddress.getByName(hostname);
 
 
            OdeslatVlakno odeslat = new OdeslatVlakno(ia, 4000);
            odeslat.start();
 
            PrijimatVlakno prijimat = new PrijimatVlakno(odeslat.getSocket());
            prijimat.start();
 
        } catch (UnknownHostException ex) {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
 
}
class OdeslatVlakno extends Thread
{
    private InetAddress server;
    private DatagramSocket klient;
    private int port;
 
    private byte addPacket[]=new byte[3];
    private String test="add";
    private String key1 = "1234567891234567";
 
    public OdeslatVlakno(InetAddress adresa,int port)
    {
        try {
            this.server = adresa;
            this.port = port;
            this.klient = new DatagramSocket(5000);
            this.klient.connect(adresa, port);
 
        } catch (SocketException ex) {
            Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    public DatagramSocket getSocket()
    {
        return this.klient;
    }
    @Override
    public void run()
    {   try {
 
            byte[] key2 = key1.getBytes();
 
            SecretKeySpec keySpec = new SecretKeySpec(key2, "AES");
 
            Cipher cipher = Cipher.getInstance("AES");
 
            cipher.init(Cipher.ENCRYPT_MODE, keySpec);
            //addPacket = test.getBytes();
            //DatagramPacket testPacket = new DatagramPacket(addPacket, addPacket.length, server, port);
            //.send(testPacket);
            BufferedReader cteni = new BufferedReader(new InputStreamReader(System.in));
            while (true) {
                try {
 
                    String poRadcich = cteni.readLine();
                    byte data[] = poRadcich.getBytes();
                    if (poRadcich.equals("/q")) {
                        break;
                    }
                    byte[] nactenaData = cipher.doFinal(data);
                    DatagramPacket odesilanaData = new DatagramPacket(nactenaData, nactenaData.length, server, port);
                    klient.send(odesilanaData);
                } catch (IllegalBlockSizeException ex) {
                    Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
                } catch (BadPaddingException ex) {
                    Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
                } catch (IOException ex) {
                    Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        } catch (InvalidKeyException ex) {
            Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchAlgorithmException ex) {
            Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchPaddingException ex) {
            Logger.getLogger(OdeslatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}
 
class PrijimatVlakno extends Thread
{
    DatagramSocket klient;
    private byte[] prijimana = new byte[256];
    private String key1 = "1234567891234567";
 
    public PrijimatVlakno (DatagramSocket pomA)
    {
        this.klient=pomA;
    }
 
    @Override
    public void run()
    {   
        try {
            byte[] key2 = key1.getBytes();
            SecretKeySpec keySpec = new SecretKeySpec(key2, "AES");
 
            Cipher cipher = Cipher.getInstance("AES");
 
            cipher.init(Cipher.DECRYPT_MODE, keySpec);
            while (true) {
                try {
 
                    DatagramPacket prijimaci = new DatagramPacket(prijimana, prijimana.length);
                    klient.receive(prijimaci);
                    byte encrypt[]=prijimaci.getData();
                    byte dekodovani[]=cipher.doFinal(encrypt);
                    String vypis = new String(dekodovani,0,dekodovani.length);
                    System.out.println(vypis);
                } catch (IllegalBlockSizeException ex) {
                    Logger.getLogger(PrijimatVlakno.class.getName()).log(Level.SEVERE, null, ex);
                } catch (BadPaddingException ex) {
                    Logger.getLogger(PrijimatVlakno.class.getName()).log(Level.SEVERE, null, ex);
                } catch (IOException ex) {
                    Logger.getLogger(PrijimatVlakno.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        } catch (InvalidKeyException ex) {
            Logger.getLogger(PrijimatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchAlgorithmException ex) {
            Logger.getLogger(PrijimatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        } catch (NoSuchPaddingException ex) {
            Logger.getLogger(PrijimatVlakno.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}