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New Scientist

A chip that blocks a reader from identifying items tagged with unique electronic codes may allay privacy fears over radio frequency identification (RFID) technology.

The silicon chip RFID blocker tag has been developed at RSA Laboratories in Bedford, Massachusetts. It works like a normal RFID chip but prevents tagged goods or people being tracked by scanners after a purchase has been made.

By mounting a denial of service attack on a RFID reader, the "blocker tag" removes the reader's ability to capture the unique code it would usually be able to probe.

Privacy concerns have so far stalled the widespread adoption of the tags and RSA believes the new blocker tag will make using RFID more acceptable.

"Most people think either you get privacy or convenience but you can't have both," says Burt Kaliski, director of RSA Laboratories. "We believe you can have both with a blocker tag."

RFID tags are computer chips that broadcast a unique 96-bit code when contacted by a reader that also powers them. Manufacturers and shop owners prefer them to barcodes because they uniquely label individual items, rather than just product types, and because they can be read remotely and in high volume.

But privacy advocates say that ubiquitous tagging will allow advertisers to track the intimate shopping habits of consumers. Storing this information along with the RFID codes of items that customers carry with them would allow advertisers to target individuals - a gross intrusion of privacy, they say.

The solution, says RSA, is for consumers to carry a RFID tag that has been programmed to flood the reader with responses, instead of beaming back one unique code.

A reader works by moving through each bit in the 96-bit string and probing whether any tags present have a 1 in that position and then whether they have a 0. When tags have the digit that is being queried in the correct position, they respond with a signal. Otherwise they remain quiet and the reader moves on to the next bit in the string.

The reader quickly runs through the possibilities based on these signals and can almost instantly record the presence of a large number of unique tags.

But a blocker wreaks havoc with this system. Instead of waiting for the queries that are specific to its 96-bit string, it answers every query, preventing the reader from moving on to the next bit.

Good to see my old profession is still in business... Electronic Warfare reaches the High Street!

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