How do those smart card scanners work?

BogMonkey

Lately I've been using those 5-day rambler bus passes to get around and I can't help but wonder how the hell that box scans these things. I'm the kinda person that has to take everything apart to find out how they work but the bus driver wouldn't be too happy about me taking apart the smart card scanner on the bus. Does anyone here know how they work? Is there some kinda magnetic strip in the cardboard bus pass or does it have some kinda barcode like mechanism?

amacachi

(I'm assuming all this from my limited experience with the tickets)

The ticket you buy has an RFID chip implanted in it. It basically is always emitting a weak radio signal with the details of the ticket, which the scanner can pick up.

amacachi

http://en.wikipedia.org/wiki/RFID

3rd paragraph mentions 3 types of the chips, I assume that the transport tickets are generally the passive type.

Run_to_da_hills

amacachi wrote: »

http://en.wikipedia.org/wiki/RFID

3rd paragraph mentions 3 types of the chips, I assume that the transport tickets are generally the passive type.

That is correct.

Luas and CIE operate passive chips that work off 13.56 MHz

These are self powered and are charged by the reader when "touched" When radio waves from the reader are encountered by a passive rfid tag, the coiled antenna within the tag forms a magnetic field. The tag draws power from it, energizing the circuits in the tag. The tag then sends the information encoded in the tag's memory.

markpb

RTTH is correct about the technology but they're actually considerably more advanced than RFID, which can only emit a single, unchanging piece of data. DB cards have a chip inside which is an ISO14443 contactless smartcard, capable of storing data, executing programs and performing encryption. The details of the ticket are stored in non-volatile ram and can be updated by the bus ticket reader after the correct cryptographic keys have been presented.

Run_to_da_hills

Smart cards also have privacy issues particularly when registered to a user.

Over a time a profile can build up of the user, where he frequently travels to and the exact times of his journey. In the UK the police have taken advantage of this.http://news.bbc.co.uk/2/hi/uk_news/england/london/4800490.stm

One advantage of a fully implemented registered system is that they can lock out undesirables and trouble makers from using public transport. Already TFL has noted a 75% drop in school bus vandalism since they introduced the oyster card.

BogMonkey

Interesting ****. I've never seen the actual smart cards, are they plastic or cardboard?

Run_to_da_hills wrote: »

That is correct.

Luas and CIE operate passive chips that work off 13.56 MHz

These are self powered and are charged by the reader when "touched" When radio waves from the reader are encountered by a passive rfid tag, the coiled antenna within the tag forms a magnetic field. The tag draws power from it, energizing the circuits in the tag. The tag then sends the information encoded in the tag's memory.

While energised, do these tags continuously emit an EM signal which is picked up by the scanner? How do they modulate this kinda thing I wonder.

markpb wrote: »

RTTH is correct about the technology but they're actually considerably more advanced than RFID, which can only emit a single, unchanging piece of data. DB cards have a chip inside which is an ISO14443 contactless smartcard, capable of storing data, executing programs and performing encryption. The details of the ticket are stored in non-volatile ram and can be updated by the bus ticket reader after the correct cryptographic keys have been presented.

What does DB stand for? Are these cryptographic keys (send by the scanner and picked up by the chip) modulated in radio waves?

I can see the need for RAM in smart cards since they've to constantly update information about where and when it was scanned but these 5 day ramblers simply count down from 5 to 1. They could use a far cheaper mechanism for that which involves matching the tags circuitry with an incremental variable emitted by the reader. Then again I know very little about electronics so I don't know what the hell I'm talking about. Would you say they use a similar tag in these cardboard 5-day rambler cards, as the ones implemented in smart cards?

markpb

BogMonkey wrote: »

I can see the need for RAM in smart cards since they've to constantly update information about where and when it was scanned but these 5 day ramblers simply count down from 5 to 1. They could use a far cheaper mechanism for that which involves matching the tags circuitry with an incremental variable emitted by the reader.

Cards of the type you suggest were used years ago by Telecom Eireann for prepaid calling cards. They're easy to tamper with and impossible to authenticate so while they might be cheap, they're not used very much any more. The cards used by Dublin Bus are much more flexible, although DB aren't using much of the technology right now. They're standardised across the world and mass produced which makes them relatively cheap.

Would you say they use a similar tag in these cardboard 5-day rambler cards, as the ones implemented in smart cards?

The 5 day rambler cards are smartcards, just of the contactless variety.

KC61

DB = Dublin Bus

Run_to_da_hills

These cards have a capacitor, coil and antenna embedded in them. If you soak the card in nail varnish or cellulose thinners the card will dissolve leaving the electronic components behind. A fad in the London Oyster card was to remove the plastic and place the components inside watches, bracelets.http://boingboing.net/2008/05/05/paying-for-the-londo.html

NFC mobile phones will be the next fad and will hit the shelves within the next year. No doubt that these will become attractive as an alternative to smart cards.
http://www.techradar.com/news/phone-and-communications/oyster-card-in-your-phone-coming-soon-462241