We propose the use of "selective blocking" by "blocker tags" as a way of protecting consumers from unwanted scanning of RFID tags attached to items they may be carrying or wearing.
While an ordinary RFID tag is a simple, cheap (e.g. five-cent) passive device intended as an "electronic bar-code" for use in supply-chain management, a blocker tag is a cheap passive RFID device that can simulate many ordinary RFID tags simultaneously. When carried by a consumer, a blocker tag thus "blocks" RFID readers. It can do so universally by simulating all possible RFID tags. Or a blocker tag can block selectively by simulating only selected subsets of ID codes, such as those by a particular manufacturer, or those in a designated "privacy zone."
We believe that this approach, when used with appropriate care, provides a very attractive alternative for addressing privacy concerns raised by the potential (and likely) widespread use of RFID tags in consumer products.
We also discuss possible abuses arising from blocker tags, and means for detecting and dealing with them.
You might consider this paper to be Ron Rivest's reply to Barry Steinhardt's concerns about RFID.
The Blocker Tag [PDF]