Where do RFID cards store information?

April 29, 2008 6:11 PM

[RFID filter] When you add money to an RFID metro card, does the information get stored in the card's chip or in a central database?

I know that both systems are possible. London's Oyster card stores the balance on the card rather than the central database according to its Wikipedia page. Hong Kong's Octopus card connects to the database whenever possible.

I'm specifically curious about Atlanta's Breeze Card system for MARTA. I know they use Cubic Transportation's Nextfare system, and that the data is encrypted, but I can't find the answer to my question.

If you have two identical cards (same ID) with 1 ride left and use up the ride on the first card, would the second card say it has 0 or 1 ride left?

posted by shoesandships to Technology (4 answers total)

Maybe you can find the answer by checking their policy for lost cards. If they can replace a lost card so that you can continue to use the remaining fares you had on it, then it must be in a central database. (But if they don't that doesn't necessarily mean that it's on the chip)
posted by winston at 6:15 PM on April 29, 2008

I don't know the system in particular, but "best practices" are to store a unique ID on a card and have it match up with a database. There are major problems if you don't do it that way, including opening yourself up to fraud and all sorts of technical errors.

My understanding of RFID, though, is that it's a read-only device. Your card, then, would just have a unique ID, which would be looked up in a database.

The college I attend allowed us to keep a small balance on our student IDs, for vending machines and the like. They used to do it the "wrong way" and store the balance on the card. A friend ran out of money and went to put $20 on his card, but some freak problem with the machine put hundreds of dollars on his card. I was tech-savvy enough to realize what was going on, and immature enough to look into buying a USB magstripe reader and adding some 0's to my balance.... They "fixed" the system before I could, though.
posted by fogster at 6:57 PM on April 29, 2008

There exists RFID chips that are read/write.
posted by mmascolino at 7:08 PM on April 29, 2008

I think your information about oyster cards is incomplete.

while the pay-as-you-go balance for unregistered oysters is only stored on the cards, a registered card you top up online can easily replaced when lost, giving you the full balance back (minus three quid deposit for the card). an unregistered card usually requires a credit card statement and even then they don't always do it. london transport keeps quite extensive records of where we go, what we spend on our rides and so on. going to a ticket counter to dispute a deduction usually prompts the agent to print out a quick list of the last ten or twenty stations you have swiped in or out at. I have changed my (unregistered) oysters once or twice in the time I've been here but it's fairly safe to say they still know too much about me.
posted by krautland at 2:03 AM on April 30, 2008