How to properly convert String to byte[] on text encryption/decryption in android? (Errors - WRONG_FINAL_BLOCK_LENGTH and IllegalBlockSizeException)

Question

Hello I was looking for answers in stack overflow. But any of this dont work. Could you please help me.

I'd like to do encryption and decryption text in android. Id like to do it as simple as I can. Firstly I wrote some code in java eclipse. It work fine but if i transfer it to Android Studio there is couple of errors.

I must transfer bytes[] to String because i use Firebase and this not support storing class object with bytes[]

I try to work with this hint, and many others but I have only failure.

generateKey()

private static SecretKey generateKey() throws Exception
    {

        SecretKey  key = new SecretKeySpec(org.apache.commons.codec.binary.Hex.decodeHex(klucz.toCharArray()), "AES");         

        return key;
    }

encrypt(msg)

public String encrypt(String messageText)
{
    try
    {
        byte[] data = messageText.getBytes("UTF-8");


        IvParameterSpec iv = new IvParameterSpec(iv_.getBytes("UTF-8"));
        SecretKeySpec key = (SecretKeySpec) generateKey();

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
        cipher.init(Cipher.ENCRYPT_MODE, key, iv);


        byte[] textBytes = cipher.doFinal(messageText.getBytes("UTF-8"));
        String textString = Base64.encodeToString(textBytes, Base64.DEFAULT);

        return  textString;


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

    return null;
}

decrypt(msg)

   public String decrypt(String msgText)
    {
        try
        {
            byte[] data = msgText.getBytes("UTF-8");

            IvParameterSpec iv = new IvParameterSpec(iv_.getBytes("UTF-8"));
            SecretKeySpec skeySpec = (SecretKeySpec) generateKey();

            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, skeySpec, iv);


            byte[] original = cipher.doFinal(data);
            String textString = new String(original, "UTF-8");
            return textString;


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

        return null;
    }

When I do sth like this I got error:

WRONG_FINAL_BLOCK_LENGTH

When I try to change it to simple AES with

Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);

I got error:

IllegalBlockSizeException:

Do you get the WRONG_FINAL_BLOCK_LENGTH in the decrypt ? You should show your full decrypt methode as well, Including the code that removes the base64 before decrypt. — Ebbe M. Pedersen, Feb 11 '17 at 17:25
My decrypt looks similar to encrypt, but I edited orginal post. — Kainka, Feb 11 '17 at 17:34
As expected .. the error is the missing base64 decode in the decrypt .. :) — Ebbe M. Pedersen, Feb 11 '17 at 19:05

score 2 · Accepted Answer · answered Feb 11 '17 at 18:35

You have encoded the ciphertext in base64 after encryption, but you have not decoded it before decryption

Remove in decrypt() this code

  byte[] data = msgText.getBytes("UTF-8");

And add

byte[] data = Base64.decode(msgText, Base64.DEFAULT);

Note: do not use AES in Cipher cipher = Cipher.getInstance("AES");. Use a specific mode to avoid unexpected results in android

How to properly convert String to byte[] on text encryption/decryption in android? (Errors - WRONG_FINAL_BLOCK_LENGTH and IllegalBlockSizeException)

1 Answers1