4 ms·

> ...tamper-proof secure element... It doesn't even need to be held in anything secure, you just need to sign the balance when writing and check the signature

• shaftway 10y ago
  What's your replay attack mitigation strategy?
• throwanem 10y ago
  If your turnstiles can't talk to a server, they can't check key revocation lists, and I tend to imagine that in a city the size of New York somebody's going to leak a key every now and again - it's been known to happen with physical keys; why not digital ones, too?
  • dsr_ 10y ago
    But they don't need to have a realtime revocation list -- it's fine if a broken card works until the end of the day, or even the end of the week, as long as it stops working faster than keys are leaked or cracked. So a bus turnstile can do transactions when it returns to the garage, and turnstiles in locations where it's hard to run data for whatever reason can get a plug-in every so often on a regular maintenance run.