javax.crypto.IllegalBlockSizeException: last block incomplete in decryption - Decrypting an encrypted AES String

You should decode the string instead of encoding the platform specific representation of the string, right at the start of your method.

byte[] base64TextToDecrypt = Base64.decodeBase64(textToDecrypt);

or more precisely:

byte[] bytesToDecrypt = Base64(base64TextToDecrypt);

if you name your variables correctly.

In general, each time you (feel like you have to) use the String.getBytes(): byte[] method or the String(byte[]) constructor you are likely doing something wrong. You should first think about what you are trying to do, and specify a character-encoding if you do need to use it.

In your case, the output in the converted variable is probably character-encoded. So you you could use the following fragment:

String plainText = new String(converted, StandardCharsets.UTF_8);
System.out.println(plainText);

instead of what you have now.

So thanks to @owlstead, I was able to figure out the solution. It was that I made the mistake of Base64encoding an already Base64 encoded string. The following is by code chunk.

public static String decryptText(String textToDecrypt) {
    try {
        byte[] decodedValue = Base64.decodeBase64(textToDecrypt.getBytes());

        byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
        IvParameterSpec ips = new IvParameterSpec(iv);

        byte[] input = textToDecrypt.getBytes();

        Cipher cipher = Cipher.getInstance(ENCRYPTION_METHOD);

        // decryption pass
        cipher.init(Cipher.DECRYPT_MODE, SECRET_KEY, ips);
        byte[] plainText = cipher.doFinal(decodedValue);

        return new String(plainText);
    } catch (Exception e) {
        e.printStackTrace();
        Log.e(TAG, "Decipher error for " + textToDecrypt, e);
    }

    return "";
}

The corresponding encrypting is like this

public static String encryptText(String textToEncrypt) {
    try {
        byte[] guid = "1234567890123456".getBytes("UTF-8");

        byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
        IvParameterSpec ips = new IvParameterSpec(iv);

        // The secret key from the server needs to be converted to byte array for encryption.
        byte[] secret = ENCRYPTION_SECRET_HASH.getBytes("UTF-8");

        // we generate a AES SecretKeySpec object which contains the secret key.
        // SecretKeySpec secretKey = new SecretKeySpec(secret, "AES");
        Cipher cipher = Cipher.getInstance(ENCRYPTION_METHOD);
        cipher.init(Cipher.ENCRYPT_MODE, SECRET_KEY, ips);

        byte[] cipherText = cipher.doFinal(textToEncrypt.getBytes());
        byte[] base64encodedSecretData = Base64.encodeBase64(cipherText);
        String secretString = new String(base64encodedSecretData);
        return secretString;
    } catch (Exception e) {
        e.printStackTrace();
        Log.e(TAG, "Encryption error for " + textToEncrypt, e);
    }
    return "";
}