# PetroBlock: A Blockchain-Based Payment Mechanism for Fueling Smart Vehicles
## 1 Introduction  
The emergence of Internet of Things (IoT) technologies plays a vital role in various walks of human life, including business, agriculture, healthcare, transport, etc. According to Cisco and Ericsson, the quantity of IoT devices in daily usage will exceed over 100 billion by 2020 [1]. IoT devices, i.e., smart mirrors, smart cameras, smart cars, smartphones, etc., connect a user with a diverse range of services like traveling, manufacturing, transactions, etc., by harnessing the Internet. Most of these IoT devices depend upon machine-to-machine (M2M) communication, which involves communication without humans' intervention. The M2M communication-based systems are capable of automating the process transaction through online payment systems [2]. Although M2M communication transactions are broadly being harnessed across the globe, the context data in M2M communication have a severe concern regarding security and privacy. The contemporaryM2M-based applications face three significant challenges: (i) transparency, (ii) interoperability, and (iii) trust [3]. Transparency is one of the most significant issues faced by IoT and M2M-based applications. The current IoT and M2M devices are highly insecure in nature; therefore, communication among them must be secured by employing different encryption techniques. Moreover, data ownership is also non-persistent in these devices. Encrypting IoT and M2M infrastructure involves huge complexity. Interconnection among peripherals enhances productivity in industrial settings as well as residential area. However, when the quantity of devices increases and network connections expand due to increased population, the issue of interoperability arises. The third challenge involves the trust of users. Figure 1 illustrates an example of M2M communication wherein a smart vehicle uses limited-range wireless communication (e.g., Bluetooth and NFC) to make payment for refueling while the user of the smart car trusts vendor by providing credit card information. The smart car and gas station are equipped with IoT applications that hold the digital wallet of a user. The M2M and IoT applications that exchange physical or digital assets of users should be reliable and provide risk-free interfaces during transactions. However, the current IoT applications do not hold a consistent structure for the security, access control, and privacy-related models [4]. This raises serious concerns related to the safety and reliability of transaction processing. Recently, there has been a boom of the latest Information technology Blockchain [5]. The concept of blockchain is deemed as a decentralization ledger shared among all connected networks. Since it is not feasible to mathematically update the ledger, cryptographic-based methods are employed for the said purpose. The data structure of a blockchain comprises immutable, ordered, and timestamped data blocks. Each block in a design holds a connection with the preceding block, which forms a strict order. In a blockchain, the first block is known as the genesis block used to create the blockchain blocks, also known as block zero. These blocks consist of multiple ordered transactions. Such data structure allows provenance wherein a transaction has a single origin. All users involved in the blockchain network authenticate and approve the transaction. It is a decentralized technology wherein all records are maintained at different locations. This decentralized behavior enables blockchain to govern under multiple entities, indicating that governments or other authorities do not have any access to that. Therefore, the data in the blockchain system could not be altered. Figure 1: A typical smart pump IoT application which persist user information (e.g., credit card). Blockchain has significant properties that directly address the challenges of Intelligent Transportation System (ITS). Therefore, the companies dealing with financial services emphasize on using blockchain because it ensures highly secured transactions of assets [6].