Few times ago I have published an article about two RFID locks that I encountered while traveling and a rough blackbox analysis of these two technologies. Unfortunately, back then, I only had few samples of key cards regarding Vingcard’s locks and that led me to take false assumptions.
But I was lucky enough very recently as to meet this lock once more. And because it was a three weeks stay, it was pretty easy to purposely tell the reception that my card was not working anymore, a couple of times, in order to have them reprogram it (yay, I’m a bad guy!). The purpose here was, first, to check what values can change over time (they usually encode the duration of the stay instead of the checkout timestamp) and secondly, to ensure that there is not a kind of timestamp-dependant key.