private byte[] createChecksum() {

        try {
            InputStream fis = new FileInputStream(file);

            byte[] buffer = new byte[1024];
            MessageDigest complete = MessageDigest.getInstance("SHA1");
            int numRead;
            do {
                numRead = fis.read(buffer);
                if(numRead > 0) {
                    complete.update(buffer, 0, numRead);
                }
            } while(numRead != -1);
            fis.close();

            return complete.digest();

        } catch (FileNotFoundException e) {
            System.out.println("Geen inputstream kunnen maken");
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            System.out.println("Geen MD5 algoritme kunnen laden");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("Bestand niet kunnen lezen");
            e.printStackTrace();
        }
        return null;
    }