1 Introduction

The global population residing in urban areas has rapidly increased over the last few years. Between 2018 and 2050, the worldwide urban population is expected to rise by 2.5 billion, with about 90% concentrated in Asia and Africa. Thus, around two-thirds (68%) of the global population will have settled in urban areas by the middle of the century [1]. The global urbanization trend has drastically enhanced the quality of people’s lives in several domains, including healthcare, literacy, transit, economic system, and working and living conditions. However, the global rise in urban dwellers is often accompanied by additional difficulties and challenges. Due to the growing population levels, residents’ living conditions are drastically impacted by traffic jams, air pollution, greenhouse gas emissions, and waste produced. Such concerns drives residents to formulate innovative solutions for the economic growth of the cities as well as the enhancement of their standards of living [2, 3]. The concept of ‘Smart City’ is presented in this regard.

Although the term ‘Smart City’ doesn’t have a commonly agreed-upon definition, but Fernandez-Anez attempted to provide an initial categorization of the various denotations of a smart city [4]. The conceptualization of a smart city is contingent on the location and on the level of growth, desire to adapt and improve, assets, and expectations of the city dwellers. In Europe, a smart city might have a different meaning than, say, America [4]. Every urban resident has a list of infrastructure and facility requests that reflect his or her level of expectations based on their perception of a smart city. One way to define a smart city is it being a metropolitan area where sensory information is gathered using IoT devices and further leveraged in applications, resources, and facilities effectively. The sensory data obtained from residents, machines, and resources is currently being stored and evaluated for tracking and controlling traffic and transit infrastructure, power stations, services, water management, waste management, law enforcement, colleges, medical centers, and municipal facilities.

The Smart City framework combines Information and Communication Technology (ICT) and distinct smart devices connected to IoT systems in order to maximize the performance of community activities and engagement with people [5]. Such systems allow local representatives to communicate with the resources of both the society and the public to track of the region and its progression. ICT is used to improve the efficiency, productivity, and functionality of public facilities in an effort to minimize expenditures by lowering the usage of resources, and to maximize interaction between people and governance in a friction-less fashion [6, 7]. Smart cities improves people’s quality of life through various positive implications, including enhanced transparency, civic engagement, efficient traffic and public transit maintenance, optimum usage of resources, greater security of the ecosystem, smart app monitoring, and enhanced medical, power, and educational facilities.

In this paper, we will will go over the brief history of Blockchain, classifying its various types and providing a detailed descriptions of its architecture. We will then delve into the various ways that Blockchain can be integrated into a plethera of smart city domains that include smart governance, smart transportation, smart grids, smart management, trade & finance, smart healthcare, smart home, e-commerce, and others with a scope of development. Additionally, this paper will provide areas of interest where Blockchain can be analyzed further to promote the development of smart cities application and services using Blockchain.

2 Blockchain systems

The blockchain, simply put, is a digital database that is transparent, distributed, unchangeable, decentralized, and accessible to the public. Everyone on the blockchain network is given access and can authenticate the transactions recorded on it. It organizes the data into blocks, that are chained together hence the name blockchain. Every block will have several transactions, and each transaction is represented in Hash form. Hash is a unique address allocated to each block during its development, and any further change in the block would result in changing its hash code.

2.1 Classification of blockchain systems

There are four main types of blockchain system: public blockchains, private blockchains, consortium blockchains, and hybrid blockchains. The primary distinguishing feature of each system is its access rights. This section aims to distinguish between each system by listing its benefits, drawbacks and ideal uses. Figure 1 offers a high-level illustration of the intersecting and mutually exclusive features of the described blockchain types.

Fig. 1
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Classification of blockchain systems

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2.1.1 Public blockhain

A public blockchain is permission-less. Meaning, anyone from around the world can join the network and read, write, or participate in the authentication process. Additionally, users can log a transaction and even receive a copy within the blockchain itself. There is no single entity that has complete control over the network. Thus, information stored on the public blockchain is safe, as data is unchanged or unaltered once authenticated. Ethereum and Bitcoin are two widely used public blockchains [8].

2.1.2 Private blockhain

Private blockchains, also known as permissioned blockchains, have some set of restrictions on who can access them and participate in the transaction and validation process. Only pre-selected entities will have the access rights to the blockchain [8]. Participation of nodes is determined either by providing some rules or by the network will determine the access control policies. This pushes the system towards using a centralized network, which distracts from Nakamoto’s stated primary blockchain features of decentralization as well as transparency [8]. These are generally used in private organizations to store confidential details that can be accessible by only a certain number of people in the organization. The data is within the organization and should be beyond the control of any other entities [8].

2.1.3 Consortium blockhains

A consortium blockchain offers a combination of both public as well as private blockchain attributes. In consortium blockchain systems, few users manage the consensus process, while other users participate in the transactions [8]. It is public because it is not controlled by a single entity, but rather it is shared by various users [8]. It is private because every user cannot access the blockchain(restricted). So, it is partially public and partially private [8].

2.1.4 Hybrid blockhains

Hybrid blockchain is a distinct form of blockchain technology that combines elements of both public and private blockchains or attempts to use the best aspects of both public and private blockchain solutions. In a hybrid blockchain, transactions and data are rendered private but may be validated as necessary, for as by granting access via a smart contract. Although private information is retained within the network, it is nevertheless verifiable. Even if a private organization owns the hybrid blockchain, it cannot alter transactions. A hybrid blockchain enables organizations to set up a private, permission-based system alongside a public, permissionless system, allowing them to control who has access to specific data stored in the blockchain and which data is made public.

2.2 Architecture of blockchain systems

The blockchain architecture consists of the elements like a node—user or computer that has a complete copy of the blockchain ledger, block—a data structure used for keeping a set of transactions, and transaction—the smallest building block of a blockchain system. As mentioned, blockchain is a distributed journal where all parties hold a local copy. However, based on the type of blockchain structure and its context, the system can be more centralized or decentralized. This simply refers to the blockchain architecture design and who controls the ledger. A private blockchain is considered more centralized since it is controlled by a particular group with increased privacy. On the contrary, a public blockchain is open-ended and thus decentralized. In a public blockchain, all records are visible to the public and anyone could take part in the agreement process. On the other hand, this is less efficient since it takes a considerable amount of time to accept each new record into the blockchain architecture. In terms of efficiency, the time for each transaction in a public blockchain is less eco-friendly since it requires a huge amount of computation power compared to private blockchain architecture (Fig. 2).

Fig. 2
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Architecture of blockchain systems

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2.2.1 Transactions

The smallest elements of the blockchain network are transactions. Transactions are organized in the form of a block and distributed to every node in the network. Whenever a transaction is added to the network, every node validates and processes them individually. Each transaction is time-stamped.

2.2.2 Blocks

The block in a blockchain network holds all the transactions that are shared across the network. Each block consists of a block header with certain data, the hash value of the current block, and the last one is the hash value of the previous block. Cryptographic hash algorithms are used for generating hash values for each block which helps in identifying the block easily in the blockchain network. Whenever a block is created, it automatically attaches a hash value to it. Any changes that are made to the block can be identified using hash values. The hash value of the previous block plays a vital role as it creates the chain of blocks and is an important element behind the blockchain architecture.

2.2.3 Peer-to-peer network

The blockchain is a peer-to-peer network. All peers can equally access and participate in the transactions of the network while interacting via a consensus algorithm. These types of networks are generally more secure as they will be no common point of failure as in the centralized systems. The sole responsibility of the peer-to-peer network is to create a decentralized network.

2.2.4 Consensus algorithm

The consensus algorithm is a rule that every user of the network is expected to obey [9]. There is no single entity to validate and verify the transactions, but still, each and every transaction in the blockchain is secured and verified [9]. This is achieved through a consensus algorithm which is a core part of the blockchain network [9]. This procedure ensures that whatever local copy each entity has, is synchronized with others and is the latest one. Proof-of-Work and Proof-of-Stake are some widely used consensus algorithms [9]. Consensus can be achieved in a blockchain network by using the Proof-of-Work algorithm. It is the original consensus algorithm first used in Bitcoin [10]. It validates the transactions and then generates new blocks in the blockchain. The time taken for creating a block is around 10 min. Nodes that perform these validations get rewarded. Hash algorithm-based mathematical problems can be solved. The usage of this algorithm proves that the nodes spent a lot of time in solving this problem and restraining data forgery [11].

2.2.5 Proof-of-Stake algorithm

An improvement to PoW is the Proof-of-Stake algorithm. It is designed to mitigate the limitations of PoW. Some nodes in the blockchain network are responsible for creating new transactions. These nodes are known as validators in Proof-of-stake. In order to participate in creating new transactions, the validations will increase the stake values. All nodes that are validating the next block increase their stake. The validators with the highest stake value will be likely selected for carrying out new transactions. The most common methods for selecting the validator are coin-age and randomized block selection. The validator then generates the blocks by validating the transactions. In the randomized block selection method, the process of selecting validators is done by searching for nodes with minimum hash value and maximum stake. In the coin-age method, node selection is done depending on the time the coins are staked [12]. When a block is generated by a node, its coin-age will be reset to zero thus giving other nodes priority over the current node in the generation of a new block [12]. This mitigates the dominance of the nodes having a large stake. The validator will lose their stake, in case the block is not verified by others [12].

3 Smart cities

The concept of smart city was first proposed by International Business Machines Corporation (IBM) in 2008 as a solution to the ‘smart earth’ strategy. Smart city is an application of the IoT system that connects public resources, such as power grids, highways, and water supply systems via various types of embedded smart sensors [13]. This system dynamically retrieves the key information from the sensors, thus, the analysis and integration of the data resources generated in city operations might be performed to achieve refined resources and efficient configuration, which would facilitate intelligent governance and the operation of production activities leading to a sustainable development of the city [13].

3.1 Characteristics of a smart city

Smart cities can strengthen and develop their facilities and amenities by leveraging smart technologies, software, and data. That requires exposure to water and electricity supplies. Ensuring affordable housing for all, providing better education and health care, and increasing IT accessibility. Smart cities can upgrade or build unplanned and badly planned places, such as slums, with a goal to keep communities secure and less disaster-prone. Using surveillance cameras, illegal activity will be monitored, and significant safety steps will be implemented to secure women, children, and elderly people.

A significant variety of public services will be made more easily available to citizens. Services will be delivered digitally, particularly by using mobiles to minimize charges for services and offering facilities without heading to government offices [14]. It’ll have increased transparency, accountability as well as civic engagement. E-group creation would allow citizens to express their views and to provide suggestions, track programs and events with the assistance of cyber tour worksites. The development and preservation of parks play areas and leisure areas would mitigate urban impacts. Living spaces will be designed to meet the increase in population and to improve their quality of life. Increasing accessibility to public transit and innovative approaches such as smart parking, traffic management, and advanced modal transit. Smart cities should be more pedestrian and bike accessible with essential administrative facilities at reduced walking distances.

By minimizing the quantity of waste produced and even by making good use of natural resources, infrastructure would be more efficient and eco-friendlier. Smart Cities pursue a goal of enhancing sustainability and maximizing people’s standard of living by transforming and redeveloping urban communities by leveraging technologies to achieve successful outcomes. Smart cities will employ technologies and data in order to develop their facilities and upgrade their services. It would significantly improve the standard of living, generate more employment and raise wages for everyone, specifically those from a lower-middle-class background. Smart city infrastructure will allow cities more sustainable and competitive, which is essential in consideration of the anticipated rapid increase of urban residents in the coming decades. Consequently, in accordance with the research done by BCC [15], in IT sector of the global smart cities market will reach about $800 billion by 2022. Smart City is a global phenomenon in the usage of advanced technology, economic growth, and a better standard of living for its residents and particularly focused on sustainability. Due to the above factors, implementation of blockchain technology in smart cities makes sure of the data integrity, encourages organizations such as healthcare, schools, colleges, governments, and citizens to exchange data and make collaborative decision-making, openness in the city maintenance and foster the execution of a reliable, transparent, safe and democratized smart city [16]. The Fig. 3 shows a few of the applications of smart cities where blockchain technology can be implemented. The rest of the paper discusses how blockchain technology is used in government, transportation, management, trade & finance, and some other services in smart cities.

Fig. 3
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Applications of smart cities

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4 Blockchain in smart cities

4.1 Smart governance

Blockchain technology is emerging rapidly because of its huge potential to enable smart governance services.

4.1.1 Smart government

Many Blockchain applications were introduced for various Government sectors, as there are explored to enhance the cost of their operations [9]. Blockchain technology has the ability, in the digital government sense, to promote direct connections between public bodies, people, and economic agents. Blockchain decentralization is the key innovation that will reshape how governments communicate with people and with each other. For carrying out economic activities, the government can use blockchain technology for storing and sharing data. Rather, the government will have a superior role in carrying out the transactions that occur within the network [17]. For exchanging information between public administrations, blockchain technology can be used as an interface. Instead of simply registering in a centralized way, distributed registration of documents and properties is argued to offer both technological and economic benefits [18]. As blockchain technology is a distributed network, it may generate uncertainty with respect to network stability, as it eliminates one control point. In the banking sector, the controlling power is among the centralized entities(banks), whereas if we implement blockchain technology in this sector, all the users will be given equal privileges [19].

4.1.2 Digital identity

Digital identity is one of the most important aspects which helps the government to identify each individual or entity uniquely. It also helps the citizens to access all the online services offered by the government more securely. It is becoming a focus for individuals, companies, and public authorities, as the aspirations of users are to take ownership of their data as they use many of the current digital services [9, 20]. One example is the cities that are embracing Blockchain technology to innovate their city services in Estonia. Estonia is implementing a digital identity system. There is an electronic chip inside each Estonia ID card that contains, the data about its citizen owner, two certificates, one for authenticating the identity and one for having a digital signature. This ID card can be used in many online environments, for example, purchasing public transport tickets, online elections, and many other city services [3]. One more example is that the digital identity network in Canada provides its citizens to maintain all their information privately and they themselves can decide on the information that is being shared with service providers [21].

4.1.3 Voting systems

Current voting systems rely on the central electoral authorities to organize the voting process and vote counting. This requires a lot of trust from the representatives, and the security flaws are faced by the central agencies [22]. Using blockchain technology we can implement a decentralized service for voting. An e-voting system can be implemented with the help of smart contracts that can be executed in a decentralized network. An e-voting system should be secure, thus not allowing duplicate votes, and also securing the user’s identity. These systems are safer, simpler, faster, transparent, and more user-friendly [23]. Ethereum offers a blockchain platform that can be deployed using smart contracts. All functions in the Ethereum network are (at least intended to be) in real-time, and all the blocks are written in the overall chain in exchange for some Ethers (the Ethereum network currency). In the Ethereum network for the confirmation-of work, there is no necessity of a centralized entity. All peers are free to measure the contract results without any intervention. The Ethereum network can also provide self-tallying [24].

4.1.4 Tax collection

Taxation is critical for running a government. This generates funds not only for the government’s routine operations but for national infrastructure, civil service, and defense programs as well. It contributes to a fiscal deficit and prevents economic growth as governments struggle to recover taxes from the populace. Hence, tax collection is important for the government [25]. The tax system usually includes complex filing processes that are modified in accordance with new rules. The dynamic method of following the tax remission procedures is difficult to manage. Because of this, citizens sometimes refuse to make use of the tax laws [26]. This process is also difficult for anyone who isn’t sufficiently educated regarding tax rules and regulations. Governments collect taxes from organizations as well as people on the basis of their salary, revenue earned from their sales, and financial activities. The tax collected by the government which is known as Value Added Tax (VAT) depends on the products that are purchased. Implementing blockchain in the tax collection system allows the government to collect the taxes easily and it also makes the entire process of collecting taxes secure. As blockchain technology offers a secure, open, and decentralized way of storing data, it will help the authorities to maintain the tax records of payment [27]. Alkhodre et al. [28] provides a decentralized model for validating tax processes. This architecture offers a platform for exchanging the CoA (Certificate of Arrival) documents which avoids the necessity of keeping various modules. Two smart contracts are integrated into the blockchain to manage the sharing of data among various companies. It also includes the criteria to check if a transaction is valid. Ethereum framework is used to implement this architecture. Blockchain-based smart contracts help the government to minimize the difficulties in the process of tax collection. As a result, blockchain-based smart contracts will automatically deduct the tax amount owed. Based on the government rules, tax returns can be generated [29].

4.1.5 Conveyance of funds challenge

Every agency receives a budget within the Federal Government and is charged with the responsibility of using those funds to carry out its activities. A permitted blockchain will allow allocation of the budget and monitoring of funds at each phase of the process [30]. Such a program will provide the opportunity to perform a complete audit of the transfer of funds from allocation to final spending, and to do so quite instantly, at any time, simply by reading every sequential record in the ledger [31]. An organization must document all transfer funds, whether intra-agency, inter-agency, or external, allowing the immediate responsibility and allocation of funds to be made available. Expenditures that are considered sensitive may have certain aspects shielded by encryption so that only approved users could see full details of such transactions, while also providing a less comprehensive view for other users [32]. To some extent, decentralization is challenging, as it is inconsistent with the hierarchical systems of states, companies, and marketplaces, as we know them today. The privacy and organizational effect of blockchain implementations should therefore be considered by governments, considering their fundamental differences with conventional information infrastructures [33] (Table 1).

Table 1 Overview of smart governance, smart transportation, and smart grid applications
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4.2 Smart transportation

In recent years smart vehicles have gained widespread interest [43]. For vehicles, to communicate with each other thus making them smart, internet access is required which is discussed in [44] mentioned as Intelligent Transportation System (ITS). Smart transportation focuses on offering comfort, convenience for both drivers and passengers, reducing traffic and transit quality, and enhancing road safety for vehicles. The features of blockchain technology help in sharing the information mostly in public transportation such as local buses. Blockchain technology helps in building a decentralized, transparent, and safe transportation system [45]. A few of the use cases of blockchain in transportation are:

4.2.1 Vehicle-to-vehicle communication

Vehicle communication management is used for controlling traffic and also helps in mitigating accidents. Enhancement of traffic safety can be achieved by sharing traffic-related information among vehicles. Inaccurate messages that suspicious vehicles exchange have a negative effect on other vehicles in the traffic. So, an efficient trust management system in-vehicle networks have to be built in an untrusted environment [34]. As the deployment of smart vehicles has been increasing rapidly, it is difficult for a trustworthy centralized agency to manage a huge number of vehicles. So, a decentralized system helps in building trust more effectively. Blockchain’s characteristics of decentralization, accountability, and immutability make it a perfect option for this kind of system. Allowing vehicles to share information related to roads is another difficult task [46]. An effective announcement system called CreditCoin which is based on blockchain is discussed via an aggregation protocol and it also identifies suspicious users by ensuring that announcements are made accurately. In addition, a blockchain-based reward system is discussed to enable vehicles to interchange the information related to roads by earning some credibility points called the Coins [35].

4.2.2 Electric vehicle charging management

Electric vehicles have gained widespread interest in developing green transport systems and are also being used in many countries. Specifically, in cities charging stations are greatly used in order to guarantee regular driving. In fact, electric cars must pay a certain amount of cash for charging vehicles. A smart contract-based blockchain system for carrying out charging services securely for electric vehicles is implemented [36]. A localized peer-to-peer method named PETCON based on blockchain is discussed for enhancing the exchange of electricity between PHEVs. For charging and discharging PHEVs, a double auction mechanism is implemented in PETCON [37].

4.2.3 Blockchain-based ride-sharing service

Transportation is an important area for sharing economy. People tend to travel and there are always vacancies while riding personal vehicles. Sharing a ride helps in minimizing fuel costs and travel costs. Ride-sharing had gained publicity and specialists think it is a good option for minimizing traffic jams. A ridesharing service model names SmaRi is developed using Blockchain technology. Benefiting from the blockchain architecture, the SmarRi model mitigates the problems and conflicts, thereby enabling a more robust management structure and improving driver-passenger interactions. Cryptographic methods make blockchain registered information permanent, irreversible, time-stamped, and secure. In a blockchain system, every block keeps a copy of the transactions held in the blockchain in order to maintain the decentralized network [38].

4.2.4 Integrated smart parking system

Parking authorities have experienced enormous difficulties in maintaining city parking services to minimize pollution and the misuse of property because customers switch to the necessary, affordable, and sufficient parking area. There’s been a lot of work to create innovative parking solutions. Despite this, city commuters faced difficulties in reserving the parking place of their choice. The user always has to be physically present to check out the empty parking spaces [39]. Often, they must pay high parking rates because parking spaces are available a little further away. To resolve such issues, city people need a system that helps in searching all the details in an organized manner under a shared platform named Integrated Smart Parking system [39]. An integrated smart parking network puts together a number of parking infrastructure vendors under a common platform to share information with smart city riders. The main components of this network are a parking authority, a blockchain system, and a rider. The parking authority manages the details related to parking spaces, and parking charges. The blockchain system contains a shared ledger and it can be updated only when the transactions are valid. A rider is a person who requests parking the vehicle. This system provides multiple interfaces for carrying out communications [40].

4.2.5 Universal transit payment/ticketing

The process of obtaining and using tickets is often fragmented and time-consuming, particularly across various public transport modes. Some who want to ride multiple trains, get on a bus, and then rent a bike can need to make four separate transactions [41]. There are many reasons for not using public transportation. By deploying the blockchain system and the use within the framework of a common clearing and settlement currency, commuters can now buy transit tickets from the starting point to the destination in a much simpler and time-effective way. A blockchain-driven platform will provide a one-stop-shop for such a transaction inefficient legacy systems and processes. Thus, offering a superior user experience to the commuters, and saving time and money in the process [42].

4.3 Smart grid

Demand for electricity is increasingly growing along with the progress of the industrial era. The smart grid concept was introduced to ensure efficient delivery of and for securing the supply of electricity. It will maximize energy usage by setting consumption patterns, suited to a specific situation, taking into account different parameters such as the house’s price, user preferences, or appliance parameters of the house [47]. The current centralized power grid system cannot handle multiple users and consumers, so a blockchain-based power system is a smart grid phenomenon. Blockchain technology helps in enhancing smart grid systems’ reliability, data protection along with the development of transparent, secure, and efficient power systems [48,49,50].

4.3.1 Energy trading

[51] provides a new infrastructure that uses digital technologies for creating a decentralized network. The main objective is to use renewable energy resources. This framework brings together all the consumers and producers by deploying renewable energy. From production to usage, most of the power grids rely on one-way communication. Whereas the smart grids incorporate remotely controllable machines and automate the activities of every consumer. The grid will become smarter with this kind of two-way communication. In [52], it describes a bidirectional system taking Digital-Grid-Router as a platform. This model uses energy coins for keeping track of energy being shared. All the transactions based on blockchain are carried out with the Ethereum network. When the user requests energy, its flow is controlled with the help of DGR and once the electricity sharing is complete, the energy coin is updated.

4.3.2 Securing smart grids

Data security is very critical in smart grid systems for both power companies and their customers. On the one side, consumers want to prevent overpayment and to learn how their machines use the energy. On the other hand, incorrect data can deceive a grid system’s control center into making bad decisions which could lead to system instability and economic losses. So, maintaining accurate data and reliability is important for power providers and their users. Blockchain’s striking features like its unchangeable nature and decentralization make it ideal for the protection of data, reliability, and consistency in these systems. [53] proposes a data protection framework focused on blockchain to strengthen the data security of the power systems. Smart meters act as a block for measuring consumption thus ensuring its reliability and accuracy in the blockchain system. The Advanced Metering Infrastructure AMI is proposed in [54] which smart meters are used to gather information regarding power consumption. All this information is helpful at the time of billing. After the consumer clears the payment, the smart meter generates a new node for further validation steps in the blockchain. This helps in charging the customer with the information stored on the blockchain. AMI system is not only limited to power trading, it can also be used in the networks like water and gas for carrying out billing transactions [55].

4.3.3 Energy management

Energy management is one of the most hazardous issues affecting smart cities due to the complexity of the product and the vital role it plays. In this regard, it is essential for every smart city to come up with energy management techniques to avert the problems associated with it [56]. The generation of energy in smart cities has attracted the attention of most cities in the world. Most of the smart cities have adopted a mechanism of generating energy that has less pollution to the environment for instance biomass generation [57]. It is also a suitable alternative for minimizing emissions and meeting the energy demands in those cities. These cities require a lot of energy generated to meet the various technological activities. Smart cities have gradually moved to a system that produces cheap renewable energy. The cities have adopted complex energy storage systems that ensure that several kinds of energy such as thermal, kinetic, and electric are incorporated. These energy systems serve various purposes in the energy sector. They have contributed to the integration of renewable sources and the delivery of demand systems in the cities. The storage ensures that energy is stored in the right way when not needed. This enables the cities to streamline the net load shape and hence making it more efficient in the production of energy. The electric energy storage systems have participated immensely in demand-response mechanisms in the smart cities by aiding in the management of the demand curve and hence streamlining ups and downs [58].

There are various storage technologies that have been enabled by blockchain. Batteries have been modified to store electric energy in the form of chemical energy. Such batteries are manufactured in a way that is efficient and compatible with the storage of electrical energy [59]. The demerit associated with these batteries is the high prices. In addition, they have potential environmental hazards, a reduced life cycle, and are limited to the amount of current and voltages they can hold. Due to the environmental hazard they may have, they are continually being reduced from the market. Similarly, blockchain has initiated a fast response where energy is needed in large amounts like in the case of frequency control systems. The electric energy is stored in a magnetic field which is produced by the direct current flow [60]. Another form of storage in smart cities is in the form of hydroelectric. It utilizes a potential power of water from lower to high elevation reservoir that at the end produce electricity through the turbines.

The infrastructure of the smart cities’ electric power grids has to exhibit the highest technology since they are the foundation of such cities in terms of energy [61]. They enable the transmission of power from the generators to the final consumers [57]. Therefore, they have to be effective and reliable. Smart cities dropped conventional grids due to the inconveniences and the technical hiccups associated with them. Such conventional grids are associated with a lack of efficient communication systems and unidirectional barriers which affect energy transmission hence delaying some of the processes in the cities [62]. The cities have therefore adopted infrastructures that have the potential to meet the increased consumer demands. Such infrastructure grids are resilient to attacks and are never affected by natural calamities [63]. They are the best quality incorporating both microgrids and an integrated power-source structure. These systems have the capacity to interchange power or even work separately in situations when some of the grids have to be maintained or have technical hikes [59].

4.4 Smart management

Smart management helps to run the smart city project efficiently and effectively by closely looking at smart city initiative as a unique complex project and identifying projects of the smart city majoring in the successes and the practices and challenges. Most general factors like IT that promote the transformation to the smart city should be considered as policies to guarantee a successful implementation of the project [64]. A smart city project needs smart management made of people to enable the environment to make effective management and organization to participate in the success of the project. The management should have a clear vision based on the city vision the goals, objectives baseline measurement systems from the start of the initiatives. The management should demonstrate strong leadership and define the project structure and the method to manage the project. There should be a framework for the realization of benefits which should be brought about by project management institutions for organizations to identify the advantages and align them with a formal strategy in order to make sure the project benefits are gained and delivered during project execution and sustained at the end of the project. About the managerial and operational aspects in speeding up the work, available workforce, labor market flexibility. Smart management should also focus on humans as they make the smart city so smart.

Smart management involves the management of other measures to put into place the blockchain and make the smart city a successful project. The measures involve smart payments, smart waste, smart water, and security [65]. Smart management is more intelligent when it is related to a higher number of smart city fundamental measurements, which are economy, administration, living, environment, individuals, mobility, and individuals [66]. This has made the entire globe to be happy to receive smart city innovation for keeping their country on the bend of this world full of competition [67, 68]. That is, blockchain has to use the internet that enhances effective transactions without any complications. These IoT gadgets are interconnected through remote systems administration for the machine-to-machine interchanges [69]. When smart management is led by quality leaders with vision help to make more advanced choices that make everything work effectively [70]. Thus, this shows IoT is very essential in helping the effective running of smart cities [71, 72]. A huge number of IoT gadgets are utilized in smart cities and make enormous information for granting smart administrations managing the city, good water supply, smart waste management, administration conveyance improvement, and other agreeable administrations [73].

4.4.1 Smart payments

Providing essential services in smart cities is based on two areas that involve; smart payments and identifying citizens eligible for a given service. Many services like transport, information systems, and utilities are not freely offered. Hence, smart cities look for the best payment technologies to enhance easy and convenient methods of payment for the citizens. Smart payments in blockchain are applied in the transport sector globally through the introduction of transit cards that can be used in different modes of transport. The card entails the person’s identity and can be used by students disabled. Examples of these cards are the NOL card in Dubai and the Kyiv smart card. Sometimes mobile wallets pay for transport. Paying for utilities or services like power, gas, and water is essential for smart city residents. Smart payments can be done through debits through the bank, online portals, and bill collection centers. Smart payments are also applied in the acquisition of public facilities. These include parking spaces, recreational facilities, community halls, public areas. In national parks camping sites are booked through smart payments and booking of barbeque pits. Mobile payment is also a form of smart payment. Blockchain enhances access to secure and government-supported mobile payment apps. These apps or applications are easy and convenient options to transact. Between the involved parties to enhance a cashless city [74]. The data obtained from smart payments will be utilized to meet the goals of a smart city. For instance, information obtained from transit cards can be used by the management body to improve the transport sector hence smart transport. They facilitate, embedding digital payment culture technology which enhances the quality of life. Globally, smart payments have enhanced the best modes of payments in smart cities [75]. Blockchain has been the best-used mode of payment that has influenced the growth of smart cities. Blockchain mostly does not encourage middlemen in paying thus reducing loss and increasing profits in trading [76]. Ongoing studies delineate that significant smart management can spare a high amount when it embraces the use of blockchain. This is said it could happen by giving a smart transportation framework and furthermore give plenty of chances and advantages by giving a superior nature of administrations. In this connection, smart management could assist with running smart cities proficiently and adequately (Table 2).

Table 2 Overview of smart management and smart grids breakdown
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4.4.2 Smart waste

Smart waste is managed technologically currently in the smart city blockchain project. Here, the use of sensors to measure the trash bin fill level. The results of the measurement are forwarded to the cloud for analysis. This enhances the planning of the trash collection and the routes the trucks use to be optimized. This smart waste management involving technology was used to provide a solution to the sensorless solution. Through the use of blockchain in waste management the stakeholders like customers use the provided platform for making requests regarding the collection of waste. The customer service officer in the municipal council makes the request for the collection of waste instead of customers. Inspectors visit the areas for the survey, contactors are then responsible for managing operations in the waste management department. Police perform legal actions and finally, the Admn manages the waste management system. Therefore, blockchain provides a transparent and easily traceable way to control waste management [77]. Blockchain eradicates problems associated with waste management like issues of fraud and manipulation this is done through enhancing monthly reports when contractors dispose of the waste. The problem associated with a lack of integrity is solved as every data collected is timestamped and immutable. Blockchain also controls information loss or wrong information and how documents are streamlined.

The application of automation through cyber-physical systems can effectively turn waste management practices smart in the smart city paradigm. In this context, the chapter provides insights into the current trends of the applicability of IoT techniques, including radio-frequency identification (RFID) techniques, sensors and actuators, embedded systems, and wireless mobile communication technologies for effective waste segregation, real-time collection, optimal transportation, and future perspectives considering product lifecycle for the reduction in waste generation and increasing waste recycling for achieving circular economy in the smart cities [78].

4.4.3 Smart water

Blockchain is also being applied to solve water issues in smart cities. It has helped in solving water conflicts among citizens. To solve this blockchain has enhanced water transparency through the distribution of transparent, secure ledger accounts. Here, the data cannot be modified or any corrupt behavior by the government. water quantity and quality can hence be used to make quality and better decisions to solve problems of water scarcity. This data is used by consumers in deciding if to conserve or consume water [79]. Blockchain also ensures cooperation for smarter water management to solve issues associated with water monopolies. Blockchain is working together with the Internet of Things (IoT) to make water systems smarter efficient and safer. Through the use of IoT, water distributions have smart sensors to collect data on the quality and pressure of water. The sensors send each other data to report on leaks, contamination, and burst. This then reaches water managers to control pressure to prevent much damage. IoT gives more insight and control over all parts of the city in water networking.

Therefore, this review summarises first both existing and potential applications related to network-based UWI, characterised by different spatial and temporal resolution of measurement and control data. Second, a comprehensive analysis of ICT is provided, which is extended with exemplary applications in the field [80]. The analysis reveals that a coordination between intended application and usable communication technology is required to realise an efficient monitoring and control network in the field of UWI networks [80].

4.4.4 Pollution management

Smart cities have shown a big step in pollution management. According to statistics, climate change has the potential of increasing the number of deaths by more than a hundred thousand due to air pollution. This is one of the key challenges that smart cities are dealing with. Various artificial intelligence platforms have been developed to assess big data and predict the areas of poor air quality. The information that is provided by the big data sources has helped to reduce air pollution in various parts of the cities [81]. Besides, IoT is also applied in weather and natural disaster management and disease control in smart cities [82]. IoT Libelium sensors have been used in these cities to monitor mobile technology, hence minimizing pollution. These sensors are used in combination with other tools such as static sensing stations. These devices provide quality and accurate data which help in mitigating pollution. Similarly, smart cities have been competent in mapping pollution. Various technologies are used to achieve this. Google cars are embedded with sensors to collect data from the environment [60]. The information obtained from the mapping processes is essential in providing loud and clear data that can be used by city dwellers to predict further challenges associated with industrialization. There are also mechanisms developed to deal with dense clouds of smog in the cities [83]. Dense clouds have a potential impact on environmental pollution if not dealt with within the appropriate time. They result in overhead pollution which may increase the effects of climate change and the greenhouse effect. Towers such as the smog-free tower in Beijing have been constructed with the right technology to clean air within a short period and use a minimal amount of power. This process involves breaking the compressed smog particles to help reduce environmental covering. These particles are therefore used to make rings and cufflinks [57]. Most of the smart cities in the world have plans to eliminate diesel and gas vehicles from the road in the next 20 years and come up with hybrid cars or electric-generated cars by 2030. This mechanism will have a positive impact in mitigating air pollution within the cities.

4.5 Trade and finance

Blockchain has features that can be of great use in the financial sector. One of these features is its ability to create one version ledger. This ledger is then shared across multiple computers enabling access [85]. This is important in the finance industry as it’s an effort towards transparency. This encourages the workers in that department, as they know of the progress of their department even without being called in for the annual general meeting. This also affects the senior personnel who use the time they would have spent on elaborating on the progress of the organization on other fruitful activities. This also makes easy the work of compiling financing reports as this single ledger holds all the financial transactions of the organization. Another feature suitable for finance is that of a smart contract. This technology works to facilitate, verify, and enforce contracts [86]. Through this technology, the buying and selling of property are made more transparent as there are no more middlemen. All the rules and requirements passed during this contract are enacted and enforced automatically. There exists a code that acts as a mode of settling the contract in that if payment is made the party receives a key to unlock that code. This technology is useful in banks and other money lending institutions as the contract the two parties signed can be enforced automatically reducing the cases of delayed payments.

4.5.1 Privacy protection

Specialists proposed different privacy protection approaches on the blockchain such as a novel privacy-preserving methodology namely RZKPB and FPPB [87, 88]. In [87] authors found it challenging to find a way in maintaining a balance between speed and privacy of transactions. To solve this problem, a novel privacy-preserving method RZKPB was suggested. By using this method, the financial transactions are held from the public point of view as they do not store in the blockchain system. In this study, the researchers used an online platform in sharing economy to present RZKPB in their project. The outcome of this study indicated that RZKPB is more efficient than already available blockchain-based privacy-preserving methods [87]. In another study conducted by Wang et al., an additional privacy-preserving method was proposed namely the Fast and Privacy-Preserving method which is based on the permissioned Blockchain (FPPB) for carrying out transactions securely. The outcome of the study indicated that FPPB preserves the confidentiality of transactions. It would not be able to target the authentication protocol and introduce new off-blockchain contact. Moreover, Ethereum is used to implement the experiments to assess the efficiency of FPPB. The method only slows down transactions slightly relative to regular transactions [88].

4.5.2 Financial transactions

Coyne and Onabolu [89] mentioned that Blockchain technologies support peer-to-peer financial transactions, where deals in a shared record specify payer, payee, date, amount, and the services to be exchanged such as a bank statement, Uber service, energy services. Also, expert practitioners have to draw peer-to-peer contracts with their knowledge, or at least conform to contract templates put together [89]. According to Wang et al., Blockchain is a constantly rising list of records, which uses cryptography to make all records connected and secured. A centralized problem, like a single-point failure and suspicious actions, has been effectively resolved in the sharing economy [87]. In a 2019 study, Pee, Kang, Song, & Jang proposed a new trading platform. By incorporating the energy exchange framework introduced in this document, the security issue can be solved and applied via the blockchain private network. Also, by using the peer-to-peer, transparency and immutability would be developed by accomplishing the automatic transaction. Therefore, there is no need to include a third party when using the smart contract [90].

4.5.3 Financial exchanges

Trade & finance in a smart city needs blockchain technology for financial exchanges, both household and universal, which identity with exchange receivables fund and worldwide exchange [91]. An example of these trade finance exchanges incorporates loaning, giving letters of credit, calculating, sending out credit and protection, and so on. These exchanges make up a large segment of worldwide exchange. Practically whenever products or administrations are purchased or sold over any fringe, there is some type of exchange account included. Blockchain innovation permits the production of a computerized record of exchanges that can be dispersed among an advanced system by utilizing cryptography. One of the challenges engaged with the exchange fund is the enormous volume of paper records that despite everything make up a significant part of the data stream. Banks are looking to decrease expenses and increment effectiveness by swapping the progression of paper for exchange funds with computerized information streams [92]. Blockchain innovation permits the production of a computerized record of exchanges that can be dispersed among an advanced system by utilizing cryptography [93]. Blockchain guarantees that it might be able to streamline the exchange account process. Along these lines, every member of the system can safely change that record without the requirement for a local authority [94].

All smart cities are embracing blockchain technology due to its effectiveness. In the modern era, the development of smart cities has led to the high utilization of blockchain technology [95]. For instance, automation in blockchain-based sharing administrations is the most remarkable component of administration connections between associations. A single blockchain can encapsulate the entirety of the important data in one computerized report, which is refreshed in a split second and perceptible by all individuals on the system simultaneously [96]. The mechanization of blockchain-based business has pulled in critical enthusiasm for different enterprises. Given the highlights of being sans trust and democratized, blockchain innovation has empowered business exchanges with outsiders without the requirement for a confided-in middle person. In the interim, the product can robotize a great part of the exchange procedure, permitting legally binding vows to be implemented without human contribution [97]. Among the best of blockchain’s points of interest is the accelerating of exchange settlement time (which at present takes days), expanding straightforwardness between all gatherings, and opening capital that would make some way or another be attached upholding on to be moved between parties in the exchange.

4.5.4 Banking sector

Given that banks deal with clients’ money it’s very important that the methods they adopt are safe and transparent. One of the impacts this technology has had on banks is that of increasing accuracy. Before adopting this technology, many banks relied on their workers for accurate financial reports. Errors were a common thing and through the blockchain, errors were minimized to almost none. This is because of its ability to consolidate the many financial transactions into one single ledger making it easier for adjustments, balancing, and compiling of final reports. In addition to that, the technology allows for the personalized access of client’s data where all transactions a client does with that bank are cryptographically posted in a way that only the client can decrypt and understand it.

The use of the blockchain has reduced the cases of embezzlement. This is due to the ability of this technology to protect its data from alterations. Once data has been entered through this technology it cannot be changed to meet the expectations of another person. Before its existence, people used to alter transactions to meet their desired results to cover their mistakes and misuse of funds. Attempts to alter data in a blockchain are made difficult by a cryptographic hash function, which reports any attempts to hack into the system through results. It uses the avalanche effect, which reports any small attempt to alter figures bypassing these changes through the entire block until the results report a huge difference [98]. The bank is therefore in a better position to identify the cause of their financial deficits as the technology allows them to backtrack all the changes to the original false entry and rectify it. They will also be in a position to stop any acts of fraud before they are affected.

Blockchain has also made cheaper the Know Your Customer (KYC) regulations. Before the technology, many banks had spent huge amounts of money on these regulations. For instance, JP Morgan spent 1.6 billion euros on additional expenses for the extra staff [99]. The banks that apply this technology have had their clients upload their identities to the blockchain. This reduces the procedures the client and the bank have to undergo to have the details. In addition to that, the blockchain allows another bank to access these clients’ details after they have shown interest in transacting with them. The data can also be used by a branch of that bank to perform transactions. This reduces the expenses banks have to use will acquiring and following the regulations (Table 3).

Table 3 Overview of blockchain’s impact on the banking sector
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Blockchains have also enabled faster cross-border transactions. Banks have for a long time experienced the problem of timely cross-border payments. In most cases, payments made from one bank to another take 2–5 days. SWIFT transfers from one bank to another take a long time [100]. This is due to the existence of middlemen. Blockchains remove the need for middlemen and hence save on time and money. Transactions become more efficient and economical. This has been experienced when SAP collaborated with ATB Financial and fintech Ripple and sent the first blockchain money transfer payment to Germany from Canada. This transaction was done in 20 s.

Blockchain technology offers a platform where assets can be exchanged without intermediaries. Banks can use this technology. This technology uses a digital token that acts as the certificate for authentication in that it shows the change of ownership. This increases the trust between the trading parties in addition to protecting their data using cryptography in a way that only these two parties have access to it [101]. This helps the bank reduce the cases of double-spacing hence maximizing their profits. If many banks are willing to pick this technology up, there is a big chance of saving a lot of money spent on middlemen and saving time used up in the trade transactions.

Banks use credit reporting to determine if a person is creditworthy. This means that numerous people fail to get loans and credits although they may be in dire need. However, with blockchain, peer-to-peer borrowing has been introduced [102]. These loans are fast and more efficient. Banks evaluate the creditworthiness of a person by checking the assets he has, his credit score, or his financial status. The credit score compiled by the credit institutions may not provide the correct information hence leading to poor decisions. This information about clients too can be dangerous in case it lands on the wrong Hans and therefore the use of peer-to-peer borrowing becomes the safer option.

4.6 Others

Few studies that were also performed by adopting blockchain technologies to other smart city areas are discussed below in areas like e-commerce, using smart devices in smart homes, the healthcare industry, and the administration of digital rights.

4.6.1 E-commerce

E-commerce has been very prominent in our lives in recent years. There are many benefits of implementing blockchain technologies in e-commerce, such as storing and exchanging information securely, decentralized networks, and encrypted user information [103]. Collective business approaches were usually helpful to every stakeholder. Though, the challenging part is the lack of trust between the stakeholders. In [104], blockchain-based smart contracts systems are implemented to promote trust between stakeholders in collective business approaches. The history of transactions that are registered in the blockchain is unalterable. Managing the logic of the business process can be done with the help of smart contracts. Credibility has its significance in business activities for stakeholders. The credibility of the stakeholder calculates how much other stakeholders believe him and is measured based on his past dealings and relations with the remaining stakeholders. A peer-to-peer credibility system based on blockchain is introduced [105]. Once the customer’s demand is met, a transaction containing one-dimensional data is forwarded to the blockchain. All credibility points of the user could be determined on the basis of the data recorded. Managing human resources plays an important role in the management of organizations. The reliability of human resource data strongly affects the choices made by users. In [106], a framework for human resource management based on blockchain is introduced to improve the reliability of information about human resources and all the data is maintained in the private blockchain which is developed by the organization, and only the employees are given access.

4.6.2 Smart home

We can see numerous smart devices being deployed in the coming years. Smart devices play a key role in building smart homes. An interactive medium should be developed between these devices to provide few facilities in a smart way. For example, if the lights have to be turned on instantly whenever anyone arrives home, the lightbulb has to seek information directly through other devices. Smart home user makes use of a private blockchain to control the interaction between the devices [107,108,109]. The history of interaction between local devices is stored as a blockchain transaction. The smart home user should be able to manage the interaction between devices. All these devices must be authenticated by the smart home user in order to carry out interactions through a common application. Resources like electricity and gas are commonly utilized in any home. Normally, payments for this energy consumption can be done by mobile phones or debit cards. Nonetheless, paying automatically is a phenomenon in the prospective smart home with no manual interference. Smart contracts-based blockchain system allows in carrying out automated payments. A secure smart gas payment system based on blockchain is proposed [110].

4.6.3 Smart healthcare

The advances in medical science have significantly benefited the population [111]. As the global populace is increasingly urbanizing, conventional healthcare might not be enough to satisfy the needs of the people. There are many components that contribute to the realization of smart healthcare that helps in improving the standard of living for patients. The most critical element for treating patients effectively is their health-related information. In smart healthcare, the exchange of patient data between various hospitals will be helpful for doctors to assess the health of a patient and also helps in taking the appropriate actions regarding the patients’ health, including in rural areas. Implementation of blockchain provides many benefits for the healthcare industry [112, 113]. All the health-related information can be recorded using blockchain technology securely and also no alterations can be performed. Patients can keep a track of how their health-related information is being used and can control accessing their information easily. A decentralized way of storing patients’ health records digitally which incorporates blockchain with some other technologies known as Electronic Health Records is discussed in [114]. BigchainDB [115] based on blockchain helps in storing patient records. The data is analyzed using big data tools. An architecture that allows patients to safely access as well as monitor their personal information regarding health is proposed [116]. In [117], a solution based on blockchain for the efficient and safe exchange of healthcare information between institutions is discussed. To manage private information related to their medical condition and allowing to safely exchange this information digitally between patients and doctors, a blockchain system is utilized [118]. All the patient-related information is maintained in a data warehouse using blockchain. Blockchain stores only the rules for accessing the data and encrypted connections of the medical data. MeDShare, a framework based on blockchain is discussed [119, 120] for providing cloud service providers with the provenance, auditing, and accessing the data.

4.6.4 Smart education

In the education sector, the essential activity is to manage the student’s data which includes course records and degrees. Almost all educational organizations store the student’s data using their customized format. To ensure the safety of academic degrees we can make use of blockchain technology. The information regarding the academic degrees can be maintained using blockchain technology by creating hash values for each block. For authenticity and integrity of academic diplomas, digital signature and blockchain structure are used [121, 122]. EduCTX is a blockchain-based education credit platform, where the nodes of the blockchain system are Educational Institutions, students, and organizations. This system provides a platform for collecting, maintaining, and storing information about students that can be trusted by everyone [123]. PoW is being used to track the data and blockchain functionality. Therefore, data integrity and availability will be maintained [121] (Table 4).

Table 4 Overview of E-commerce, smart home, smart healthcare, smart education, and digital rights
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4.6.5 Administration of digital rights

The administration of digital rights attempts in regulating the usage, alteration, and dissemination of copyright material. Nevertheless, some significant capital is being invested for keeping the network running and stable, contributing to higher surcharges. The nature of electronic information makes it very simple for this information to be corrupted, reproduced, and distributed. As a decentralized technology, the blockchain provides good protection. Once the information is stored in the blockchain, it becomes unchangeable. Such blockchain characteristics will encourage the administration of digital rights. Owing to the difficulty in the administration of digital rights, numerous ideas, and systems in cryptography were introduced in the past few years. The blockchain-based system that manages the rights without a centralized entity is discussed [124] which helps in managing the rights efficiently and securely. This framework is built by using Bitcoin technology. Information about rights is stored on the blockchain in the trial system. To minimize the delay in adding the blocks in the blockchain, the PoW algorithm can be altered in such a way that the interval time is reduced. In this model, only the licenser can manage all the permissions. These permissions granted along with the software are stored on the blockchain. In [125], a digital rights management (DRM) system is discussed in which broadcast encryption technique is used which enables to distribute of the data securely in such a way that only valid users can access it. A blockchain-based method for the administration of digital rights is proposed [126] which ensures the standard of the media network and in securing the digital rights. Transaction management is required to keep a track of all the transactions between the users and the media administrators. A peer-to-peer method for payment helps in minimizing the cost of payments. Every user can track all the transactions recorded on the blockchain thus not allowing false transactions. Digital signatures and hash chains ensure the security of copyright transactions. Digital rights management is of great importance to secure intellectual property. The blockchain generally encourages the management of copyright by storing information about copyrights. The unchangeable data recorded on the blockchain helps in resolving conflicts concerning copyright. In addition, by utilizing smart contracts we can manage these transactions in an automated way.

5 Conclusions and future work

In this survey, we discussed how the emerging blockchain technology can be implemented in a smart city. We started our analysis with some background knowledge about blockchain technology and smart city. After which, we discussed some of the areas like smart government, smart transportation, smart management, trade & finance, smart grid, smart healthcare, smart home, and others where blockchain technology can be implemented to enhance the growth of smart cities. We had also explored a few of the benefits and the issues that are faced in implementing blockchain in different fields of smart cities.

These days, smart cities have numerous problems to resolve and lots of open opportunities. Blockchain is also one of the most significant technologies nowadays because of its boundless advantages. In our perspective, blockchain is a disruptive technology that will push the progress of potential smart-city-related applications. Key features like decentralization, transparency, security, immutable play a vital role thus making the blockchain a platform to enhance the potential of IoT and smart-city growth [127]. As it is known, the records on the blockchain are openly accessible. In a smart city, transparency makes the resident informed and willing to understand how every one of them participates and also how government utilizes information. It is however feasible to encrypt data in case of need (i.e. confidential or personal data) before it is recorded within the blockchain. The greatest benefit of utilizing blockchain is that it is resilient against multiple attacks. Thus, the inclusion of blockchain technologies in smart cities with smart devices would build a shared platform in a distributed environment where the interactions among devices are reliable.

Blockchain technology has tremendous capacity in promoting smart cities in multiple ways which are more effective and have a high standard of life. Blockchain is a rich framework for the development of all types of smart cities applications. In nutshell, analysis about the use of blockchain technologies in smart cities is relatively large and most of the problems remain unresolved. However, it is beneficial to resolve these issues and move ahead. In this survey, we presented some ideas on how a blockchain can be implemented into smart city services. It is fair to anticipate that the main objective of smart city-related research will be to alleviate the problems posed over the next few years.