KeeLoq is a rolling code cipher used in keyless entry and "secure" ignition devices in many makes of cars. While there have been slow methods for cracking KeeLoq in the past, a group of researchers have recently shown that all it takes is access (i.e., proximity) to a car's RFID key for about an hour to gather enough data from the key to inform their code cracking software, which takes about two days to run on a modern 50 node computing cluster.
For cars that have both a traditional machine etched key and KeeLoq, a thief would still need a copy of the key (or good lockpicking skills). Those cars that are really at the most risk here are ones with push-button ignitions, which do not require a physical key insertion. The Prius is of course one such car, but many luxury cars are at similar risk. It may be time for tin foil key cozies.
