## 2 Background and Related Work
### Related Work
The focus is on improving the authentication process and reducing communication burdens between vehicles and RSUs. Their designed protocol has an authority named local authority (LA) responsible for managing vehicles' anonymous information. Utilizing a third-party authority will lead to elevated expenses, as regular commissions must be paid to these entities. Also, there is no authentication between roadside units. In [39], [PERSON] et al. proposed a mutual authentication protocol for the IoV environment. This protocol can tackle various security concerns, such as identity compromise, identity theft, and replay attacks. Each vehicular user must register with a trust authority (TA), and then TA issues a smart card. The vehicular user can use the smart card to authenticate with the roadside unit. However, it is significant to note that specific vulnerabilities, such as distributed denial-of-service attacks, are not explicitly addressed in their study. Once the attacker sends multiple authentication requests to TA, TA must compare the dynamic login identity (DIDV) and value CV to the stored value. After this, the TA creates a random integer and a session key and saves them to its storage. The approach will cause a waste of storage and does not deal with the risks of denial-of-service attacks. Blockchain mechanisms are used for anonymous authentication in [40]. With the rapid advancements in modern vehicles and distributed fog services, the expansion of vehicular fog services (VFSs) is becoming increasingly important, necessitating their presence across multiple geographically dispersed data centers. Consequently, the need for cross-data center authentication arises. However, traditional cross-data center authentication models are ill suited for the specific scenario of high-speed moving vehicles accessing VFSs. These models disregarded user privacy and failed to meet the time constraints of driving vehicles. In this protocol, only the fog node closest to the vehicle is required to authenticate vehicles, after which the fog node broadcasts the authentication result to other fog nodes and records the results on the blockchain. Therefore, this paper did not consider a fog node compromise attack. Once a fog node is controlled or compromised, the reported result on the blockchain could be misleading. In [41], [PERSON] et al. proposed a mutual authentication scheme called Octopus for the edge-fog-cloud network architecture, which utilizes a master secret key for new users to authenticate themselves to the fog server. However, the scheme has a limitation: it openly transmits the user's identity over a public channel, compromising user anonymity. Also, Octopus is primarily designed for stationary smart cards and devices, which increases the risk of interference from masquerading servers. In a large-scale fog computing environment, reusing the same master password can pose a significant security risk. Cloud computing and IoT convergence have limitations for low-latency and mobile applications. Fog computing bridges this gap by bringing computation closer to end devices. However, remote and unprotected fog nodes require secure solutions, especially in IoT healthcare systems. In [42], [PERSON] et al. proposed a fog-driven IoT healthcare system authentication key agreement protocol. Fog nodes connect cloud data centers and end devices, aiming for efficient and secure healthcare services. It considers resource-constrained fog nodes, mobile healthcare devices, and low-latency communication requirements. The protocol leverages bilinear pairings to establish secure cryptographic keys among the entities involved, ensuring authentication and secure communication. It also employs an Authenticated Key Agreement (AKA) protocol, which involves three components: a fog node, a cloud server, and sensors. It introduces a security model, provides formal security proof, and defends against common attacks. The performance evaluation considers communication and computation costs.