Abstract. KeeLoq remote keyless entry systems are widely used for access control purposes such as garage openers or car door systems. We present the first successful differential power analysis attacks on numerous commercially available products employing KeeLoq code hopping. Our new techniques combine side-channel cryptanalysis with specific properties of the KeeLoq algorithm. They allow for efficiently revealing both the secret key of a remote transmitter and the manufacturer key stored in a receiver. As a result, a remote control can be cloned from only ten power traces, allowing for a practical key recovery in few minutes. After extracting the manufacturer key once, with similar techniques, we demonstrate how to recover the secret key of a remote control and replicate it from a distance, just by eavesdropping on at most two messages. This key-cloning without physical access to the device has serious realworld security implications, as the technically challenging part can be outsourced to specialists. Finally, we mount a denial of service attack on a KeeLoq access control system. All proposed attacks have been verified on several commercial KeeLoq products. MotivationThe KeeLoq block cipher is widely used for security relevant applications, e.g., remote keyless entry (RKE) systems for car or building access, and passive radio frequency identification (RFID) transponders for car immobilizers [13]. In the course of the last year, the KeeLoq algorithm has moved into the focus of the international cryptographic research community. Shortly after the first cryptanalysis of the cipher [1], more analytical attacks were proposed [4,5], revealing Amir Moradi performed most of the work described in this contribution as a visiting researcher at Ruhr University Bochum.

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