# Connected Vehicles Security: A Lightweight Machine Learning Model to Detect VANET Attacks
## 3 Related Work
### Authentication  
This section discusses some studies on authentication and highlights their common drawbacks. One of the most important and challenging aspects of VANET security is authentication [25]. Maintaining a sufficient authentication system while simultaneously protecting privacy at the same time calls for careful consideration, and continues to pose a serious challenge. [PERSON] [24] pointed out that the lack of non-repudiation functionality in symmetric key-based authentication protocols has resulted in several security breaches in VANETs. Furthermore, elliptic curve cryptography (ECC) is used in public key-based authentication techniques, which complicates protocol implementation. To overcome these issues, [PERSON] presented an authentication protocol that uses Chebyshev chaotic maps. As a result, compared to other network models, their protocol presents a model with the least hardware complexity and surpasses others in terms of both performance and security. However, it should be highlighted that the main disadvantage of this approach is how time-consuming it is [26]. [PERSON] et al. [16] pointed out that authentication techniques are essential in VANETs for building mutual confidence between interacting entities. To ensure the reciprocal verifiability of transmitted communications, a centralized trust authority (CA) is often used in traditional authentication systems. However, in situations where there is a very high vehicle density inside the network, an excessive volume of authentication requests may cause a communication bottleneck in the CA, resulting in a single point of failure. [PERSON] et al. [27] reported that authenticated key agreement (AKA) methods currently in use have two major shortcomings. First, the overhead in communication and computation is too high to satisfy the demands of applications that are sensitive to delays (delay-sensitive applications). Second, the concept of a multi-trusted authority has not been considered. [PERSON] et al. [28] indicated that traditional conditional privacy-preserving authentication (CPPA) techniques have two drawbacks. First, an extremely short transmission delay is required for traffic emergency messages, yet the overhead in communication or storage is not sufficiently low enough. Second, although side-channel attack techniques and the wide use of the system secret key (SSK) increase the likelihood of SSK breaking, traditional CPPA systems do not consider updating the SSK. [PERSON] et al. proposed a new CPPA scheme to overcome these issues. To address the first issue, they proposed a CPPA signature scheme based on elliptic curve cryptography. This scheme can protect emergency traffic messages at extremely low communication costs. To address the second issue, they designed an SSK updating algorithm based on a secure pseudorandom function and [PERSON]'s secret sharing algorithm. According to the authors, the security and privacy criteria of VANETs are satisfied by the proposed scheme. Compared to other methods, it offers a smaller transmission delay and consumes less storage space. However, [PERSON] and [PERSON] [29] indicated that the proposed CPPA scheme is forgeable, insecure, and unable to satisfy conditional privacy. A technique is required for VANETs to authenticate messages, identify legitimate vehicles, and eliminate malicious vehicles. This technique can be offered via a public key infrastructure (PKI) that uses fixed public keys and certificates. However, fixed keys violate the privacy of drivers because they enable an eavesdropper to link a key to a certain vehicle and location [30]. The primary concept behind PKI systems is that each vehicle's OBU must preload a significant number of pair keys and their corresponding anonymous certificates, which significantly increases the TA's certification management workload. Furthermore, because of its limited storage capacity, a vehicle bears the responsibility of storage management.