# Reputation-Based Blockchain for Spatial Crowdsourcing in Vehicular Networks
## 4 ReBLOM-Based Crowdsourcing for EVs Routing Problem with Recharging Station
### Potential Threats  
In the vehicular networks, there are some widespread security threats [40] related to authentication, availability, integrity, and confidentiality. In particular, potential dangers whereby selfish malicious vehicle miners may cause damage to data communication and interaction security and the way our proposed scheme can mitigate the effects are listed here:  
* \"Sybil\" attack: In distributed vehicle-to-vehicle communication systems, malicious attackers can claim or register different identities to disrupt normal functioning. In the vehicular environment, selfish nodes with multiple identities and malicious intent can control other vehicles/nodes at a given moment, thereby disrupting the system performance. Considering the dynamic and fast-moving nature of the vehicular networks, such attacks are easily launched by attackers, so as to cause substantial damage to the system [41]. The blockchain has the characteristics of distributed ledgering and can utilize asymmetric encryption theory to ensure the security of information interaction/communication between blockchain nodes, e.g., ECC. Secondly, URC (see in Section 2.3) can ensure the confirmation of user identity at all stages of communication, such as the corresponding key, unreproducible digital signature and unique ID, etc. Thereby users participating in blockchain cannot be forged and duplicated. Further, based on the main-side chain mechanism established by TRC and MSC, it can realize real-time synchronization of comprehensive reputation across chains and assets, where is under the premise of correct identity verification. Finally, a trusted certificate authority based on smart contracts inside the block can also verify the identity of communicating entities to prevent \"Sybil\" attacks. * Denial of Service attack: In this kind of attack [7], malicious nodes can disrupt vehicle-to-vehicle communications by sending fake customer requests. That is, the attacker bombards the real server/host node with requests, so that the blockchain system perform excessive and useless calculations, rendering it unable to serve real requests. Hence, it may result in the consumption of computational resources and interruption of the normal service. As a result, EVs will not be able to obtain the required data, e.g., road conditions, and the stability of vehicular networks can even be undermined. In our scheme, when customers generate service requests, they will first submit their task requirements and publish to blockchain network. Once the validity of crowdsourcing tasks can be verified, the customer can release the tasks in the form of transactions after being paid (i.e., part of the incentive). Based on customer payment acting as a pledge, validity verification as a means, and penalty function (see in Section 4.3) as a defensive measure, it can verify customer identity and requests, thereby protecting the system from Denial of Service attack. It should be added that for miners, the historical honesty/dishnesty behaviors in each mining rounds will be recorded in the ledger, which is obviously bound to the unique ID. For the mining pool, a miner joins in by contributing computational resources, and the survival time indicator will serve as the most direct index to determine the historical honest behavior of miners. * Man in the Middle (MITM) attack: Malicious vehicle nodes mislead real vehicles in the vehicular networks by modifying routing information. MITM [30] establishes contact with senders and receivers, respectively, from which malicious entities obtain confidential information (i.e., keys or data), and falsify information. MITM is a critical attacker as all the vehicles can be spoofed as though the information came from real nodes. The attacker accesses the vehicular system and the sent packets, modifies the real transactions, and sends them to the sink nodes. In the formulated blockchain-based reputation system, the information exchange between vehicle nodes is realized through unique paired public/private keys.