Encrypting and Decrypting in Java

Question

I have 3 text boxes in my form.

1.To enter text- entered_txt

2.To show encrypted text - encrypted_txt

3.To show decrypted text - decrypted_txt

When I press encrypt_btn(button), get text from entered_txt and encrypt that and show the result in encrypted_txt

When I press decrypt_btn(button),get text from encrypted_txt and decrypt that and show the result in decrypted_txt

This functionality works fine but, When i use a clear button and try to use the form again Shows an exception,

Codes are shown below;

variable declaration --

byte [] input ;
byte [] keyBytes = "12345678".getBytes();
byte [] ivBytes ="input123".getBytes();

SecretKeySpec key = new SecretKeySpec(keyBytes,"DES");
IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
Cipher cipher;
byte[] cipherText;
int ctLength;

Encrypt button;

private void encrypt_btnActionPerformed(java.awt.event.ActionEvent evt) {                                            
  try{
      Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
      input = entered_txt.getText().getBytes();
      SecretKeySpec key = new SecretKeySpec(keyBytes, "DES");
      IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
      cipher = Cipher.getInstance("DES/CTR/NoPadding","BC");

      cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);
      cipherText = new byte[cipher.getOutputSize(input.length)];

      ctLength+=cipher.update(input, 0, input.length, cipherText, 0);

      ctLength+= cipher.doFinal(cipherText, ctLength);
      encrypted_txt.setText(new  String(cipherText));

  }catch(NoSuchAlgorithmException | NoSuchProviderException | NoSuchPaddingException | InvalidKeyException | InvalidAlgorithmParameterException | ShortBufferException | IllegalBlockSizeException | BadPaddingException e){
      JOptionPane.showMessageDialog(null, e);
      e.printStackTrace();
  }
}

Decrypt button;

private void decrypt_btnActionPerformed(java.awt.event.ActionEvent evt) {                                            
   try{
       cipher.init(cipher.DECRYPT_MODE, key, ivSpec);

       byte[] plainText = new byte[cipher.getOutputSize(ctLength)];

       int ptLength =cipher.update(cipherText,0,ctLength,plainText);
       ptLength+=cipher.doFinal(plainText, ptLength);

       decypted_txt.setText(new String(plainText));

   }catch(InvalidKeyException | InvalidAlgorithmParameterException | ShortBufferException | IllegalBlockSizeException | BadPaddingException e){

       e.printStackTrace();
   }

Clear button;

 private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    entered_txt.setText(null);
    encrypted_txt.setText(null);
    decypted_txt.setText(null);
}  

The exception;

javax.crypto.ShortBufferException: output buffer too short for doFinal()
at org.bouncycastle.jcajce.provider.symmetric.util.BaseBlockCipher.engineDoFinal(Unknown Source)
at javax.crypto.Cipher.doFinal(Cipher.java:2068)
at com.bit.project.NewJFrame.enActionPerformed(NewJFrame.java:140)
at com.bit.project.NewJFrame.access$100(NewJFrame.java:23)
at com.bit.project.NewJFrame$2.actionPerformed(NewJFrame.java:68)

Line 140 is ctLength+= cipher.doFinal(cipherText, ctLength);

How can I correct this code for use the form multiple times using clear button?

Answer 1

Can you try to clear out instead of setting for null? May be your encryption method is executing again and causing the issue on clearing.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    entered_txt.setText("");
    encrypted_txt.setText("");
    decypted_txt.setText("");
}