Gone in 360 Seconds: Hijacking with Hitag2

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An electronic vehicle immobilizer is an anti-theft device which prevents the engine of the vehicle from starting unless the corresponding transponder is present. Such a transponder is a passive RFID tag which is embedded in the car key and wirelessly authenticates to the vehicle. It prevents a perpetrator from hot-wiring the vehicle or starting the car by forcing the mechanical lock. Having such an immobilizer is required by law in several countries. Hitag2, introduced in 1996, is currently the most widely used transponder in the car immobilizer industry. It is used by at least 34 car makes and fitted in more than 200 different car models. Hitag2 uses a proprietary stream cipher with 48-bit keys for authentication and confidentiality. This article reveals several weaknesses in the design of the cipher and presents three practical attacks that recover the secret key using only wireless communication. The most serious attack recovers the secret key from a car in less than six minutes using ordinary hardware. This attack allows an adversary to bypass the cryptographic authentication, leaving only the mechanical key as safeguard. This is even more sensitive on vehicles where the physical key has been replaced by a keyless entry system based on Hitag2. During our experiments we managed to recover the secret key and start the engine of many vehicles from various makes using our transponder emulating device. These experiments also revealed several implementation weaknesses in the immobilizer units.

Roel Verdult and Flavio D. Garcia
Radboud University Nijmegen

Josep Balasch
KU Leuven ESAT/COSIC and IBBT