# Secure Trust-Based Blockchain Architecture to Prevent Attacks in VANET
## 2 Related Works
However, in a high-mobility and dynamic environment, it is difficult to select vehicles as CHs due to the high velocity of the vehicles. This could lead to inefficiency as well as unnecessary waste of energy of the nodes. Not only that, the periodic update of vehicles' passwords could also lead to an increased computational overhead in the network, as the OBUs need to compute the identity and password of each vehicle before a new password could be passed to the vehicle. [PERSON] proposed a hybrid approach for privacy-preserving authentication scheme (HEPPA), which combines features of pseudonym-based approaches and group signature-based approaches, with conditional anonymity [27]. According to the researchers, the real identity of an attacker canbe uncovered during the detection of a malicious activity. This hybrid approach uses a simple and lightweight pseudonym which provides conditional anonymity. The pseudonym provides a trapdoor mechanism to enable the detection of malicious nodes and subsequently revoke such users from the network. They also introduced a cloud-assisted modular architecture that acts as a certification authority (CA), which is responsible for vehicle registration and verification of their credentials. Another feature of the hybrid approach is the grouping of vehicles based on regions that are managed by the CA using similar credentials, so that attackers cannot differentiate between vehicles in the group. The scheme does not require a vehicle to manage the certificate revocation list (CRL) to reduce processing overhead on OBU and bandwidth consumption. The researchers used elliptic curve cryptography (ECC) as the cryptographic tool, in which the elliptic curve integrated encryption scheme (ECIES) is used for encryption and elliptic curve digital signature algorithm (ECDSA) is used for the signatures of the vehicles. The performance of the proposed hybrid approach was analyzed via simulation using vehicles in network simulation (Veins), in terms of communication and computation overheads, end-to-end delay, PDR, and packet loss. The simulation results showed that the proposed hybrid approach is feasible enough to enhance the privacy of users in VANET. Nevertheless, a drawback of this approach is the region-based grouping of vehicles in the highly dynamic and high-speed network. Vehicles enter and leave a region quickly due to their high velocity, therefore increasing the difficulty in managing the groups by the CA. [PERSON] proposed an efficient, scalable, and privacy-preserving authentication (ESPA) protocol using a hybrid cryptography approach for inter vehicle communications [28]. ESPA is comprised of two phases--Phase I: V2I pre-authentication, and Phase II: V2V authentication. After off-line registration of vehicles and RSUs, the beacon signal of each vehicle is pre-authenticated by RSU during V2I communication to verify whether the vehicle belongs to any base stations in the network or is an unauthorized vehicle. The pre-authentication is carried out using asymmetric public key infrastructure (PKI). In the second phase, only vehicles that have been pre-authenticated can get involved in the V2V communication. ESPA considers V2V communication covered by the same agents of trusted authority, with vehicles having the same secure keys. ESPA was evaluated via simulation using NS-3.23, as well as traffic simulators, simulation of urban mobility (SUMO), and mobility model generator for vehicular network (MOVE), considering a two-lane, two-way highway. From the simulation analysis, ESPA was found to reduce transmission and computation overheads. According to the researchers, ESPA provides better security and meets the privacy properties requirements in VANET. [PERSON] proposed a secure privacy-preserving authentication scheme for VANET with cuckoo filter (SPACF) to enhance the security and privacy of users, as well as to minimize the communication overhead [29].