DerivationParameters param = new KDFCounterParameters(sessionKey, null /* prefix */, suffix /* suffix */, r /* r */);
        gen.init(param);

        byte[] derived = new byte[16];
        gen.generateBytes(derived, 0, 16);
        return derived;
    }


    /**
     * @param string
     * @return null terminated ASCII bytes
     */
    private static byte[] toCBytes ( String string ) {