> On the smart card, there is a value in nonvolatile memory that represents the amount of money on the card. When you add money, the VTM increments that value.

> On the smart card, there is a value in nonvolatile memory that represents the amount of money on the card. When you add money, the VTM increments that value. > Of course you can see the problems with this scheme: couldn't anyone just write a bigger number to the card? In my college days we had a vending machine which worked with a NFC card. I bough a NFC reader/writer, and quickly found out that the amount of money was exactly as described above. After a couple of tries I found out that the maximum amount of money was 22€. Free snacks for a couple of years until they changed the machine to accept only cash. No, I'm not ashamed. EDIT: The cards were anonymous, even if the machine somehow tracked the card use (I have no idea if they did), there was not way to trace it back to a person