Abstract
Vehicular Ad-hoc Networks (VANETs) have potential applications in improving the efficiency and safety for intelligent transportation systems. The openness of VANETs, however, also introduces privacy and security implications. Despite a number of conditional privacy-preserving authentication (CPPA) schemes with anonymity and conditional traceability have been designed for VANETs, a majority of these schemes cannot be directly applied to a real-world setting (e.g., due to the need for a certificate manager for issuing keys in PKI-based solutions, or the inherent key escrow problem in ID-based solutions). There have also been attempts to design blockchain-based CPPA schemes, but these schemes may not support key revocation or are inefficient (e.g., due to on-chain operations). This paper proposes an efficient blockchain-based CPPA (EBCPPA) scheme, which is designed to mitigate the above limitations. Our proposal consists of two key building blocks, namely: signature of knowledge and smart contract. To evaluate the feasibility, we present the security and performance analyses of EBCPPA. Specifically, the performance evaluations show that EBCPPA is more efficient than other existing state-of-the-art solutions, in terms of signing (improving at least 49.71%), the verification (improving at least 32.84%) and bandwidth requirement (reducing at least 27.59%).