## 6 IoT Security Solutions
### Blockchain-Based  
[PERSON] et al. showed the application and performance of blockchain in the case of IoV in [254]. It presents how data flow and re-transmission are related to network traffic growth. Security details will be considered in their future work. To make faster transaction confirmation and speed up new users, this work established a novel debit-credit mechanism for blockchain-based (PoW) data trading by [PERSON] et al in [255]. A vehicle can loan from multi vehicles as per demand by promising to pay interest and reward. It uses a two-stage Stackelberg game to maximize the profits of borrower vehicles and lender vehicles jointly. Nash equilibrium is reached when there are optimal pricing strategies. To make the account secure, it uses encrypted signatures using corresponding keys and certificates. It is assumed that an adversary cannot forge a signature of a vehicle or gain control over the majority of system resources. A blockchain-based incentive mechanism has been proposed by [PERSON] et al. in [256], where multiple vehicles can participate in bidding to allow their resources to complete a task through a smart contract for secure transactions. The method identifies malicious bidding by unusual price and quality of data provided. If any vehicle is identified as a malicious vehicle, then it will be removed from the network and it will not get any reward. For accomplishing any emergency task, the bidding process will be omitted, and multiple vehicles can make a cluster as per the same time allocation and resources. A novel time-window-based method is developed to manage the emergency task. Here, as malicious nodes are identified after receiving a report, a malicious incident can happen. Also, in case of an emergency task, it ignores the bidding, and the communication of inter-vehicle for clustering is not depicted which can compromise clustered vehicles and networks as well. [PERSON] et al. proposed a decentralized trust management system based on blockchain [257]. It employed a joint PoW and PoS consensus mechanism. Vehicles validate received messages from surrounding cars and calculate credibility using the Bayesian Inference Model. Vehicles consider the distance between sender and event location. Based on the result, vehicles upload ratings to neighboring RSUs and it then calculates trust offset to finalize data. RSUs work as a miner. It assumes that RSUs will not be compromised due to the limited resources of an attacker. [PERSON] et al. combined 5G network for low latency, a software-defined network (SDN) for effective network management, fog computing for avoiding frequent handovers, and an incorporated trust model to make the decision about message authenticity in [258]. The vehicles are equipped with SDN-enabled OBU. The practical Byzantine fault-tolerance consensus algorithm is used for verifying correctness. RSU hubs are used as miners, and PoW puzzle solutions are used in this blockchain method. In this method, peers provide verdicts about the trustworthiness of the information, such as time of event reporting, location of the event, etc. provided by the neighbor vehicle. The trust model is organized into three algorithms, (1) Cluster model: neighbor vehicles make a cluster, (2) Message forward model: Verdicts are collected and aggregated and forwarded the message to the other clusters in the network to create awareness. (3) Judgment model, which concerns the decision obtained over a sender's message after several verdicts. However, a Cluster should be random as vehicles are moving and no pattern follows. [PERSON] et al. proposed an energy-efficient transaction model using blockchain in [259]. This work mainly focused on fewer transactions to reduce network traffic. It used asymmetric encryption to incorporate security. Instead of sending direct data, it will send functions using an adaptive linear prediction algorithm where a certain amount of real data will be trained. If the new data is not within the preset value, it will forward the function.