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You might think being able to pay in shops with a wave of your bank card or open doors with your security pass is smart. But the RFID tags that make that possible are due for an intelligence upgrade.

Today’s RFID tags can only broadcast fixed data back to a reader device, whether that’s details of your passport or of an endangered bird. Researchers are now working to add brains to the tags in the form of microcomputers, opening the way for much smarter applications.

Because RFID tags lack batteries and scavenge all their power from the radio transmissions from their readers, limited power makes computation a challenge. But that also has the advantage of making so-called computational RFID tags – CRFIDs – cheap, robust and long-lasting.

Batteries not included

“Ten years ago we would have thought this was science fiction – doing programming without a battery,” says Kevin Fu, who works on CRFIDs at the University of Massachusetts Amherst.

Fu and his colleagues are working on CRFIDs using hardware from Intel called WISP (Wireless Identification and Sensing Platform). Intel’s smarter tags use a 16-bit microcontroller and can store programs up to 32 kilobytes in size. They can also store small amounts of electricity picked up from a reader for short periods in a capacitor.

Because power, computational capacity and memory are all so limited, researchers have to write their code cleverly to accomplish anything useful. In fact, Fu says, they sometimes use algorithms written in the 1970s for inspiration.

Tight fit

“It’s those tight constraints that make the research so interesting,” says Ari Juels, a computer scientist at RSA Laboratories in Cambridge, Massachusetts, who is collaborating with Fu.

The Massachusetts groups have been investigating energy-efficient ways for CRFIDs to store data – a big challenge that further limits the amount of computing the tags can do.

Because they rely on external power, CRFIDs need a way to back up their computations frequently so they don’t have to start again from scratch if the power is lost. That requires flash memory unaffected by power outages, like that used in memory cards – but the memory systems in such cards are power-hungry, taking the CRFID designers back to square one.

Fu and his colleagues have developed a strategy to sidestep flash memory. They have shown it can be less energy-intensive to back up a computation by sending it back to a reader for storage, even when extra work must be done to encrypt the data first.

The technique “enables long-running computations to make progress despite continual power interruptions”, the researchers explain.

“I think that their approach to the problem is absolutely correct,” says Joshua Smith an engineer at Intel Research Seattle who leads development of WISP. “That is one of the interesting things about using RFID technology: a lot of the system-design issues turn out to be very different.”

Concrete data

CRFIDs are too new to have ventured far from the lab bench yet. But Juels says enabling them to encrypt and decrypt data could make chips in passports or credit cards more secure.

Adding sensors is another possibility. Fu’s team has tried embedding CRFIDs into concrete to report moisture content, which could give engineers early warning of structural faults.

A paper (PDF) on the team’s efficient data transmission techniques was presented today at the Usenix Security Symposium in Montreal, Canada.

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