4 ms·

I don't understand why the vending machine would trust the client to tell it how much credit the user had without first verifying from an upstream centralized d

• ddebernardy 8y ago
  My initial thought was that this was how the developers were overcoming the potential for network problems. But in that case it would have been a mere cache, so agreed on that it's bad design.
• tokyodude 8y ago
  AFAIK this is how Felica works which is the system for many of the transit systems across the world as well as a payment system built into feature phone since 2005, Android since 5-6 years ago and iPhone since iPhone7 in Japan and 8 everywhere else. https://en.wikipedia.org/wiki/FeliCa https://en.wikipedia.org/wiki/FeliCa I don't know for a fact that it works without a DB but I do know that they exist in places that don't seem to access to a DB and they work instantly (no long pause like credit cards).
  • lifthrasiir 8y ago
    It works without a DB as far as I know, and there are handful incidents where people knowingly blocked a connection to the payment system to charge the card with no money spent. Primary security measures against fraudulent transport cards had been blacklisting, which seems to work well enough as there are not much hacked cards.