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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

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    You don't store the balance on the card itself, for exactly that reason. These cards have encryption capabilities to help prevent fraud by stealing the card, but this is generally to protect individual consumers, not processors. Terminals that process Debit transactions almost always are hooked up with a realtime connection (to an ACH or the bank itself), specifically to mitigate these types of attacks - on older systems, this was the only way to verify the pin! Used for Credit they might not be, but you'd still be on the hook, so... – Clockwork-Muse Dec 2 '14 at 11:41
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    @Zaibis We have a similar system in Brazil, and I, like you, would love the answer for this question. The balance IS saved JUST on the card. – Lucas NN Dec 2 '14 at 18:54
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    superinformado.com.br/wp-content/uploads/2013/03/…, image of our system in Brazil, NO internet connection. – Lucas NN Dec 2 '14 at 18:55
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    @Zaibis "I have 10 binary identical smardcard's" And that is where you run in to a problem. The smart cards can't be copied (Without destroying them for finding a flaw in the software running on them) So there is no way to get 10 copies of the card, you will only ever have 1 copy. – Scott Chamberlain Dec 2 '14 at 22:53
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    Posting this to validate the question as worthy to be asked: Some stored value cards actually store the value on the card itself. Here is an example where the protocol (to deduct the value) is insecure, and the "deduct payment" instruction is hidden youtube.com/watch?v=vZ4MqMUO5NY – goodguys_activate Dec 3 '14 at 15:35
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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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    Great answer. I didn't know about the mc's. Your answer would benefit from some links or references to (credible) sources though. – agtoever Dec 3 '14 at 16:34
  • en.wikipedia.org/wiki/Smart_card#Design The other article is german only. – Zaibis Dec 4 '14 at 6:57
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Offline system has an overwhelming advantages of minimal infrastructure server and network cost and the transaction is fast and reliable.

There is no way you can avoid duplication even with the most advanced encryption technology of smart cards.

The preventive solutions:

  1. setting an upper limit to reduce the total lost each time.
  2. verify ad-normal transaction and ad-normal card ID and black-list them.
  3. With CCTV in place in many stores, it will discourage people to take the risk.
  • Hi, and welcome! Please, no signatures and no self-promotion. Answers should stand on their own. – schroeder Dec 20 '16 at 7:48
  • How would blacklisting work in an offline procdeure? – Zaibis Dec 20 '16 at 18:00

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