###### Abstract  
In ad-hoc vehicle networks (VANETs), the random mobility causes the rapid network topology change, which leads to the challenge of the reliable data transmission. In this paper, we propose a hybrid-price auction-based secure routing (HPA-SR) protocol using advanced speed and cosine similarity-based (ASCS) clustering to establish a secure route to avoid sinkhole attacks and improve connectivity between nodes. The main features and contributions of the proposed HPA-SR protocol are as follows. First, the HPA-SR protocol is employed by the first- and second-price auctions to avoid sinkhole attacks. More specifically, using the Markov decision process (MDP), each node can select a kind of auction method to establish the secure route by avoiding the sinkhole attack. Second, the advanced speed cosine similarity clustering protocol that is considered as underlying structure is presented to improve the connectivity between nodes. The ASCS is constructed based on the cosine similarity and distance between nodes using the speed and direction of the nodes. The results of the performance show that the proposed HPA-SR protocol can establish the secure route avoiding the sinkhole attack while the proposed ASCS clustering can support the strong connectivity. Besides, the HPA-SR with ASCS protocol can show better performance than the benchmark protocol in terms of the routing delay, packet loss ratio, number of packet loss, and control overhead.  
secural security; sinkhole attack; vehicular ad-hoc networks 20222225811 202222225811 20222225811 20222225811 202222225811 20222222 222225811 2022222 222222 222222 2222 2222 22222 2222 2222 2222 2222 2222 2222 2222 22  
In VANETs, vehicles driving along roads can be formed into groups to facilitate communication. Clustering stabilizes the connectivity between nodes by hierarchizing the network architecture, where each cluster can be divided into three kinds of nodes, called cluster head (CH), cluster member (CM), and gateway (GW) [9; 10]. When CM needs to communicate with other nodes, CM sends the message to its CH. This CH can communicate with other CHs. If the intermediate CH is out of transmission coverage, the GW helps to relay between CH and CH. When the data packet arrives at the last CH, the CH sends message to the desired CM.  
Routing protocols play an essential role in ensuring reliable data communication [11]. The routing protocol can select the suitable next nodes from a source node to a destination node among intermediate nodes. Routing in a VANET is complicated due to its dynamic nature including significant mobility and various network topologies. Therefore, routing protocols designed for the VANET environment must meet the standards of scalability, efficiency, and comparability. Recently, the security has become one of the critical issues in the network [12]. Considering the accessibility of the network and also cyber security has drawn much attention for cyber-physical systems (CPS) [13]. Moreover, blockchain [14; 15] is one of the solutions when it comes to supporting credible distributed communication, and basically having the main characteristics of decentralization, distributed consistency, etc. In VANET, there are three types of attacks. The first type is an attack on the communication infrastructure, such as routing protocols, the second type is an attack on VANET's functions, such as location monitoring, and the third type is an attack on security requirements, such as authentication protocols. The sinkhole attack is one of the network threats in which the sinkhole node announces itself as having the best path to the sink or destination node and prevents data transmission between a source and a destination node by broadcasting fake routing information [16; 17]. During the routing process, the sinkhole node can provide fake information. Therefore, the data packet sent by the source node does not arrive at the destination node.