Java encryption using AES

Question

I am trying to make an encryption system using AES class:

package Source;
import java.security.MessageDigest;
import java.util.Arrays;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.spec.IvParameterSpec;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AES {
  static String IV = "AAAAAAAAAAAAAAAA";
  static String plaintext = "test text 123\0\0\0"; /*Note null padding*/
  static String encryptionKey = "H4tch4repratygonetowil5h4kers";
  public static void main(String [] args) {
    try {

      System.out.println("==Java==");
      System.out.println("plain:   " + plaintext);

      byte[] cipher = encrypt(plaintext, encryptionKey);

      System.out.print("cipher:  ");
      for (int i=0; i<cipher.length; i++)
        System.out.print(new Integer(cipher[i])+" ");
      System.out.println("");

      String decrypted = decrypt(cipher, encryptionKey);

      System.out.println("decrypt: " + decrypted);

    } catch (Exception e) {
      e.printStackTrace();
    } 
  }

  public static byte[] encrypt(String plainText, String encryptionKey) throws Exception {
    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding", "SunJCE");
    SecretKeySpec key = new SecretKeySpec(encryptionKey.getBytes("UTF-8"), "AES");
    cipher.init(Cipher.ENCRYPT_MODE, key,new IvParameterSpec(IV.getBytes("UTF-8")));
    return cipher.doFinal(plainText.getBytes("UTF-8"));
  }

  private static String decrypt(byte[] cipherText, String encryptionKey) throws Exception{
    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding", "SunJCE");
    SecretKeySpec key = new SecretKeySpec(encryptionKey.getBytes("UTF-8"), "AES");
    cipher.init(Cipher.DECRYPT_MODE, key,new IvParameterSpec(IV.getBytes("UTF-8")));
    return new String(cipher.doFinal(cipherText),"UTF-8");
  }
}

And here is my implementation of code:

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JButton;
import java.awt.BorderLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JTextPane;


import Source.AES;
import javax.swing.JTextField;
import javax.swing.JPasswordField;
import javax.swing.JTextArea;

public class first {

    private JFrame frame;
    private JPasswordField passwordField;
    private JTextArea txtrEnterTextHere;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    first window = new first();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public first() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JOptionPane.showMessageDialog(null, "Welcome to Encryption System! ");
        JButton btnNewButton = new JButton("Send Info");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                String text = txtrEnterTextHere.getText();
                String pass = passwordField.getText();
                String str = null;
                try {
                    str = new String(AES.encrypt(text, pass));
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                txtrEnterTextHere.setText(str);

                JOptionPane.showMessageDialog(null, "Your intel has been encrypted!");

            }
        });
        frame.getContentPane().add(btnNewButton, BorderLayout.NORTH);

        passwordField = new JPasswordField();
        frame.getContentPane().add(passwordField, BorderLayout.SOUTH);

        txtrEnterTextHere = new JTextArea();
        txtrEnterTextHere.setText("ENTER TEXT HERE AND PASSWORD BELLOW!");

        frame.getContentPane().add(txtrEnterTextHere, BorderLayout.CENTER);
    }

}

How can I make the variable 'str' actually to have the value of my encrypted text? At runtime I get errors and an empty field ... is it ok to change from byte[] to string?

Update error:

java.lang.IllegalArgumentException: Empty key at javax.crypto.spec.SecretKeySpec.(SecretKeySpec.java:96) at Source.AES.encrypt(AES.java:41) at first$2.actionPerformed(first.java:62) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$500(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)

From the error, it seems something is wrong with `SecretKeySpec` constructor — Sujeet Sinha, Jun 17 '16 at 09:03
**General advice:** Please don't use a fixed IV. The IV is a non-secret value that is supposed to provide semantic security when it is freshly generated during encryption. Since it is not secret, it can be sent along with the ciphertext. A common way is to prepend it to the ciphertext during encryption and slice it off during decryption. — Artjom B., Jun 17 '16 at 10:18

score 3 · Accepted Answer · edited May 23 '17 at 11:58

You have several issues here.

You have Empty key at javax.crypto.spec.SecretKeySpec exception because you don't enter any password.
Once you enter the password you'll have an exception like Invalid AES key length: 8 bytes, because the key should be of the particular length (see more about that here).
After using hash to generate the key, you'll have the following exception - javax.crypto.IllegalBlockSizeException: Input length not multiple of 16 bytes, because your encryption mode doesn't use padding. You can change it to something like AES/CBC/PKCS5Padding

Finally with the following "encrypt" method you'll get what you want :

public static byte[] encrypt(String plainText, String encryptionKey) throws Exception {
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding", "SunJCE");
    MessageDigest sha = MessageDigest.getInstance("SHA-1");
    byte [] hashedPassword = sha.digest(encryptionKey.getBytes("UTF-8"));
    hashedPassword = Arrays.copyOf(hashedPassword, 16);
    SecretKeySpec key = new SecretKeySpec(hashedPassword, "AES");
    cipher.init(Cipher.ENCRYPT_MODE, key,new IvParameterSpec(IV.getBytes("UTF-8")));
    return cipher.doFinal(plainText.getBytes("UTF-8"));
}

(*) Of course in order to decrypt the message you'll have to do the similar changes in "decrypt" method as well...

Java encryption using AES

1 Answers1