Unlinkable Signcryption Scheme for Multi-Receiver in VANETs

An increasing number of researchers are turning their attention to signcryption, particularly in the context of multi-receiver communication scenarios, due to its ability to simultaneously provide authentication, integrity, and confidentiality of messages. However, existing signcryption schemes have not been able to fully implement sender unlinkability. Specifically, when a sender signcrypts a secret message and obtains the corresponding ciphertext, the intended recipient must use the sender's identity or public key to complete the unsigncryption process and retrieve the plaintext. Consequently, the recipient can link the sender via the same identity or public key. To address this issue, we present an Unlinkable Signcryption Scheme for Multi-Receiver (USS-MR). With Chinese Remainder Theorem (CRT), our USS-MR enables a vehicle to send the same secret message to a group of RoadSide Units (RSUs). Additionally, when a new message requires signcryption, the vehicle generates a new key pair, making it impossible for any RSU to link the vehicle through its public key. In our USS-MR, we have adopted a pseudonym mechanism to provide conditional privacy, which hides the real identity of the vehicle through the use of pseudonyms and avoids linking it to the identity. Moreover, if a vehicle is found to engage in malicious behavior, it will not only be tracked but also subjected to revocation. Comprehensive security analyses demonstrate that our USS-MR satisfies various security, privacy, and functionality requirements and effectively resists common attacks in Vehicular Ad-hoc Networks (VANETs). Finally, our USS-MR demonstrates certain advantages in terms of computation and communication when compared to relevant studies. In particular, our USS-MR maintains a consistent communication burden of $388$ bytes.