One Car, Two Frames: Attacks on Hitag-2 Remote Keyless Entry Systems Revisited

Since 2006, many papers were devoted to the analysis of the security of the Hitag-2 algorithm in the context of vehicles access control. While this algorithm was proven to be cryptographically broken, it is still in use in the car industry. Recently, new vulnerabilities regarding Hitag-2 based Remote Keyless Entry systems have been exposed, leading to the design of an attack allowing to unlock a vehicle and requiring the capture of four to eight radio packets. However, in this study, it will be shown that specific implementations of Hitag-2 based RKE systems exist, which apply interesting countermeasures and thus are not vulnerable to the aforementioned attack. Furthermore, a detailed black box analysis of such system, from the physical layer up to the rolling code implementation will be proposed. Finally, a new cryptographic weakness will be exposed, which can be exploited to forge valid packets without retrieving the cryptographic key and to open the target vehicle, requiring the capture of only two radio packets.