I don\'t know how well known this system is or maybe there are equal systems bet

Question

I don't know how well known this system is or maybe there are equal systems better known international. So I'll introduce the related points of the system:

It is a paymentsystem where your wallet is saved on the cardchip itself. The terminals you are able to pay with such a card on do not have to have a permanent internet connection.

And even if they have, the system isn't designed for synchronisation on real time. It has at least intervals of multiple hours (AFAIK even just 1 time per day) where the moneychange gets updated.

So if such terminals aren't sharing there information of moneychange in any kind of netwrok to other terminals, what is preventing a bad guy from just duplicating the chip and its data and paying with each chip on a diferent terminal? As the available money is just stored on the chip how could a terminal know that the represented ballance is invalid? Or even the chip it self is?

Of course in the synchronisation process it will get noticed. But untill that a lot of time can elapse

Explanation / Answer

I could figure out some informations about the smart card it self. The chip isn't just holding binary data which every terminal is able to access. The chip contains a micro controller which can get its own firmware set up. So the terminals aren't communicating with the stored data, they just have a API to the microcontroller.

So if you want to copy the data, you have to request the mc to read the data for you. What he ofcourse will deny.

So the other way is, to physically produce a identical chip containing the same controller with the same firmware running on, made for that chip. because only that chips own mc is able to access its binary data and read it correctly. (What sounds almost impossible to me. Even if not, the amount of money won't be enough for the work this would effort)

Or the other option for doing so is: get the controller seperated from the binary data, without destroying it. and hack the encryption he stored the data with, to be able to write plain data in the chips memory.

Without hacking the encryption we could try to shortcircuit the mc...

Even to short circuit the mc wouldn't work, as the money using terminals will use the API to the controller and are also not accesing the data directly.

And I would bet, you can't short circuit the mc, access the data directly and then set back the undamaged microcontroller, without at least making it invalid by some secruity flags or such kind of stuff.

Also notable is that the terminals in generell are just able to decrease the money amount. Such that are able to increase the money are hold by the bank it self and not given out. So they are probably on a way encrypted, that the chip contains a public key which keeps some information about how the "money decrese" has to be encrypted. What would missmatch in case of a increase.

That was all I figgured out, and I would guess this is enough to be an answer even in some one else eyes.

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