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01 April 2008, 11:41

Radio controlled door opener for cars and buildings cracked

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Scientists at the Ruhr-Universität Bochum have defeated the Keeloq immobiliser and door opener used in many cars. Attackers need only intercept two transmissions between the transmitter and receiver in order to clone the digital key and gain access to the car. Microchip Technology's RFID-based KeeLoq process, is used in automobiles manufactured by Chrysler, Daewoo, Fiat, General Motors, Honda, Toyota (Lexus), Volvo, Volkswagen and Jaguar. KeeLoq is also used in building access systems and garage door openers. Signal interception is possible at a range of 100 metres, according to Professor Christof Paar of the School of Electronics and Information Technology. In addition to gaining unauthorised access, the systems can be manipulated, denying the rightful owners access.

Both the KeeLoq transmitter and receiver encrypt their signals. A proprietary, non-linear encryption algorithm is used which encrypts controller commands with a unique code before transmission to the vehicle. A 32 bit initialisation vector together with a 32 bit hopping code is used as a key. An ID unique to each electronic key is added to the calculation.

But there is also a manufacturer's master key for all of the products in a series. This is precisely what Professor Paar's Bochum group was able to retrieve using a procedure known as side channel analysis. To obtain the master key the researchers used differential power analysis (DPA) and differential electromagnetic analysis (DEMA) at both the transmitter and receiver during the transmission. Once the master key is known, only two transmissions are needed in order to obtain the crypto key of a particular KeeLoq remote control. The vulnerability was tested on commercial systems, according the Bochum scientists.

In early February the researchers presented a detailed description of the attack that required them to intercept a number of activation procedures in order to obtain the manufacturer's key. At the CRYPTO 2007 cryptography conference, an international group of researchers presented a method by which the individual keys could be cracked using distributed computing.


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