Smartphones are quickly moving toward complementing or even replacing traditional car keys. We advocate a role-based access control policy mixed with attributes that facilitates access to various functionalities of vehicular on-board units from smartphones. We use a rights-based access control policy for in-vehicle functionalities similar to the case of a file allocation table of a contemporary OS, in which read, write or execute operations can be performed over various vehicle functions. Further, to assure the appropriate security, we develop a protocol suite using identity-based cryptography and we rely on group signatures that preserve the anonymity of group members for assuring privacy and traceability. To prove the feasibility of our approach, we develop a proof-of-concept implementation with modern smartphones, aftermarket Android head-units and test computational feasibility on a real-world in-vehicle controller. Our implementation relies on state-of-the-art cryptography, including traditional building blocks and more modern pairing-friendly curves, that facilitate the adoption of group signatures and identity-based cryptography in automotive-based scenarios.