CSAS-V: Certificateless Schnorr Aggregate Signature for VANETs

Efficient message authentication mechanisms for securing vehicular message exchange in VANETs are essential for meeting the diverse needs of real-time communication, driver safety, and data integrity. As such, certificateless aggregate signature (CLAS) schemes are widely used in this area, since they can significantly lower the communication and verification costs and overcome certificate management as well as key escrow issues that existing cryptography systems have. Nonetheless, bilinear pairings are still widely used in existing CLAS schemes, imposing a heavy computational burden and limiting scalability in high-density vehicular scenarios. In this paper, we develop CSAS-V, a novel Certificateless Schnorr Aggregate Signature scheme for VANETs. CSAS-V also utilizes the lightweight and pairing-free property of Schnorr signatures on a certificateless model to enable rapid, secure, and scalable message authentication. Our scheme achieves conditional privacy with pseudonyms, traceability with respect to a trusted authority, and strong security guarantees against both Type I and Type II adversaries under the assumption of the Discrete Logarithm Problem (DLP) in the random oracle model. Hence, we provide a thorough security analysis and show the performance of CSAS-V in terms of computational cost, communication cost, and scalability compared to recent CLAS schemes. To this end, the results show that CSAS-V provides a significant saving in the signing and verification time compared with existing signatures, without loss of security and privacy, and is particularly suitable for real-time applications in future intelligent transportation systems.