# A Low-Overhead Message Authentication and Secure Message Dissemination Scheme for VANETs
## 2 Related Works  
Cluster-based vehicular cloud architectures have been proposed in [14; 15] for infrastructureless VANETs; under these approaches, vehicles are grouped into clusters based on their location, speed, computation capability, etc. Vehicles belonging to a cluster elect a Cluster Head (\(CH\)). The \(CH\) performs the creation, maintenance, and deletion of vehicles in that cluster. A scheme in [16] proposed a similar approach, where vehicles in a specific region form a vehicular cloud elect a broker among them. The broker collects the desired data from the vehicles and then sends it to a cloud server if further processing is required. Security-related issues are not addressed in these schemes. The authors in [15] designed a secure communication protocol for exchanging messages among vehicles in a smart city using an Elliptic Curve Cryptography (\(ECC\)) technique. In their scheme, Cluster Heads (\(CH\)s) are responsible for communicating and verifying messages within their clusters, and the CHs are verified by the Certification Authority (\(CA\)). In this scheme, frequent \(CH\) elections could occur if vehicles move fast.  
Many privacy-preserving authentication schemes, such as anonymous authentication [17], cooperative authentication [10], and dual authentication [18] have been proposed. For example, [PERSON] et al. [17] proposed a PKI-based efficient anonymous authentication scheme with a conditional privacy-preserving (EAAP) scheme for VANETs. The vehicles and \(R\)SUs communicate anonymously to provide privacy and anonymity during the authentication process, and the TA can revoke a misbehaving vehicle and find out its real identity in case of dispute. This scheme is secured against different attacks (e.g., impersonation attacks, message modification attacks, etc). However, in the above schemes [10, 17, 18], vehicles communicate not only with each other but also with the \(R\)SUs to verify the authenticity of the messages.  
Schemes presented in [19, 20, 21] used \(R\)SUs for authenticating, processing, and disseminating messages received from vehicles in its region. In [19], a safety warning system in fog-cloud-based VANETs using a Certificateless Aggregation Signcryption Scheme (CASS) have been proposed. Vehicles send traffic messages to the \(R\)SUs, which act as fog nodes. These fog nodes process and aggregate the received messages. These schemes [19, 20, 21] address the security and privacy issues for VANETs. However, they do not consider heavy densities of vehicles, which may cause increased computation and communication overhead.  
In our scheme, vehicles do not form clusters among themselves. Each \(R\)SU can decide when and where to form clusters in its region, based on the density of vehicles and other parameters such as the region from which the \(R\)SU receives a large number of messages. In addition, the \(R\)SU assigns the Group Leader \(GL\) (the Group Leader is not elected) for each cluster, and the \(GL\) is responsible for collecting, authenticating, and aggregating the messages received from its cluster/group and for forwarding them to the \(R\)SU. The \(R\)SU is responsible for collecting the messages sent by the \(GL\)s in its region, authenticating them, aggregating them, and forwarding them to the vehicles in its region and/or other \(R\)SUs for further dissemination. This approach reduces the computation and communication overhead for the \(R\)SUs.