## 10 Blockchain  
A blockchain operates on a peer-to-peer network and uses cryptographic algorithms to secure and validate transactions. It eliminates the need for intermediaries, as the transactions are verified by multiple participants in the network [113]. A blockchain is the underlying technology behind cryptocurrencies, e.g., Bitcoin, but its applications extend beyond just financial transactions, including supply chain management, healthcare, and voting systems [83]. A blockchain can support optimizing energy distribution and resource allocation in a smart city. By enabling peer-to-peer energy trading and data-driven resource management, a blockchain can minimize waste, improve energy efficiency, and foster sustainability within the city. A blockchain facilitates secure energy trading within a smart grid. It allows individuals and businesses to buy, sell, and exchange energy directly, optimizing energy usage [97; 114]. A blockchain allows for the creation of a decentralized and tamper-proof ledger. By storing transactional data, contracts, and other information on a blockchain, smart cities ensure records' transparency and integrity. This transparency improves trust between stakeholders, including citizens, businesses, and government. Moreover, a blockchain can track and manage waste disposal and recycling processes. Creating an immutable record of waste generation, collection, and recycling enables transparency and accountability. This data can be utilized to optimize waste management systems, reduce waste, and promote recycling efforts [115]. Summing up, a blockchain can be deployed in smart cities to enhance their efficiency in several ways, as presented in Table 15[114; 115; 116]. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Benefit** & **Blockchain-Based Smart City** \\ \hline Transparency and trust & A blockchain provides an immutable and transparent ledger, ensuring that data cannot be tampered with or altered. This enhances trust and accountability within the city infrastructure, allowing citizens to trace how resources are allocated, ensuring transparency in decision-making processes, and minimizing corruption. \\ \hline Efficiency and automation & Smart contracts on a blockchain can automate various processes, e.g., energy distribution, traffic management, and waste management, improving efficiency and reducing administrative costs. Smart contracts can automate and enforce agreements between different entities within a smart city ecosystem. It eliminates the need for intermediaries, reduces administrative costs, and ensures transparent and efficient transactions. \\ \hline Supply chain management & A blockchain can enhance supply chain traceability in smart cities. By recording every transaction and movement of goods on a distributed ledger, stakeholders can have real-time visibility of the entire supply chain. This improves efficiency, prevents fraud, and promotes sustainable practices by monitoring the environmental impact of goods and services. \\ \hline Enhanced security & A blockchain provides a decentralized and tamper-proof system, ensuring the integrity and security of data. This prevents cyber-attacks and unauthorized access to sensitive information, ensuring a safer environment for smart city residents. \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Benefits of deploying blockchain for smart cities. Security is among the benefits achieved by deploying a blockchain for smart cities. Blockchain-based solutions can have critical roles in improving the security of smart cities. The security benefits can be summarized as follows [117]. * Transparency: A blockchain's decentralized nature ensures that all transactions within a smart city network are recorded in an immutable and transparent manner. This transparency helps identify unauthorized or fraudulent activities, improving security. * Data integrity and authentication: By leveraging a blockchain, smart cities can ensure the integrity and authenticity of their data.