The chips in these cards are a perfect example of a computer you own but don't control, and when that's a good thing. The only reason fast transit cards work i

The chips in these cards are a perfect example of a computer you own but don't control, and when that's a good thing. The only reason fast transit cards work is that the chips on them are under control of the transit agency, and designed in a way that makes it impossible for the card owner to hack in and modify the balance. If somebody finds a fundamental flaw in Suica, I suspect things will get pretty interesting indeed. If you tried to implement Suica with cards where the card owner had full control, you would have to do this with asymmetric keys, cryptographic signatures, and a round trip to the server for every transaction.