CL-ASV: Pairing-free certificateless anamorphic signature scheme for secure VANET communications

Vehicular ad hoc networks (VANETs) require efficient authentication, conditional privacy, and secure transmission of sensitive information. Existing conditional privacy-preserving authentication schemes mainly focus on message authentication and traceability, while sensitive information is usually protected by additional encryption or signcryption mechanisms, which introduce extra ciphertext components and communication overhead. Recently, anamorphic signatures were proposed to embed sensitive information into ordinary-looking signatures. However, existing anamorphic-signature schemes were constructed on bilinear groups and exhibit limited scalability when multiple hidden message blocks are transmitted. To address these issues, this paper proposes a pairing-free certificateless anamorphic signature scheme for VANETs (CL-ASV). Our CL-ASV scheme enables a specified target receiver to recover the embedded sensitive messages, and allows everyone to only verify the identity of senders without knowing the messages. CL-ASV avoids the time-consuming bilinear mapping in the authentication and verification phases and allows to embed multiple sensitive message blocks through lightweight PRF-based masking. We first present the concrete construction of our CL-ASV scheme, and then prove its security. Finally, experimental results show that CL-ASV achieves lower computational and communication overhead than existing related schemes.