On: The tiny chip that powers Montreal subway tickets

[kevincox]

You can fail open. The QR code contained a signed ticket ID and expiry. You locally validate the signature and expiry and remotely attempt to validate reuse. If the remote validation is slow or fails just accept the ticket and log it.

[rswail → kevincox]

That is what happens, however it exposes the transit company to a risk that many of them aren't willing to accept.