Efficient Key-Escrow-Free and Vehicle-Revocable Data Sharing Protocol for Vehicular Ad Hoc Network

Vehicular ad hoc network (VANET), as an important part of intelligent transportation system, attracts more and more attention since it can provide communication about traffic and vehicle conditions, and optimize the transportation. It is noted that it also faces a series of security challenges. One of core issues is how to achieve secure data sharing and access control. Ciphertext-policy attribute-based encryption (CP-ABE) technique is often used to achieve these goals simultaneously. However, in the execution process of applying CP-ABE to VANET, there are two crucial issues that need to be resolved. One is key-escrow issue, which means that all vehicles' secret keys will be leaked once if the central attribute authority (CAA) is compromised, and another is the revocation issue of departing vehicles from current region. In order to resolve these two issues simultaneously, in this article, we propose an efficient data sharing protocol for VANET with the key-escrow-free and vehicle-revocable properties. More specifically, we design a subprotocol between CAA and vehicles, which interactively issues secret keys for these vehicles. But CAA does not know any user's true secret key, which guarantees that it is still secure even if CAA is compromised. In addition, we additionally introduce an entity named group manager, which manages and updates the unrevoked users in the current group. In order to improve the efficiency of the whole system, we adopt the online/offline encryption method for data owner and outsourced decryption technique for the resource-constraint data users. Finally, the performance analysis show that our proposed protocol is competitive in the phases of online encryption, key generation and CAA-setup, and thus is useful in the practical applications of VANET.