4 ms·

Suica, Pasmo and the like are all contactless SCs. The Wikipedia page is a good start, and you can go deeper from there: https://en.wikipedia.org/wiki/Suica ht

• bschwindHN 9y ago
  Ah sorry, I mean how the machine verifies the validity of the card.
  • sly010 9y ago
    It's asymmetric key cryptography. Every vending machine can verify signatures using a CA certificate. Charging stations and a vending machines also have a signing key signed by that central certificate. Whatever is written on the card is signed by whoever wrote it. Charging a card goes like this: - Read everything from the card (data + signature) - Verify signature + expiration dates, etc - Extract amount on card - Decrement said amount - Write new amount to card - Sign data on card using local signing key It's a bit more complicated than that, but you get the idea. In some systems the logs of all transactions are reconciled asynchronously (if and when internet connection is available) so if a card is cloned it can eventually be detected and blocked.
    • bschwindHN 9y ago
      The "local signing key" is the interesting part to me. I guess only vending machines in certain areas can get IC card support. I wonder how often those local keys need to be rotated. That's a great answer though, thanks for writing it up!