# Possible Blockchain Solutions According to a Smart City Digitalization Strategy
## 3 Digitalization Strategy of City Governance
### Internal Communication  
Tailored communication channels, both formal and informal, including the sharing of documents between different parts of the city administration, need to be provided to make mutual cooperation as efficient as possible. Informal communication (inquiries about clarification of individual requests and processes, search and delivery of data that are not necessary for the continuation of the process, etc.) should be strictly distinguished from official communication, which is part of official city procedures (approval of various requests, delivery of data necessary for the continuation of the process, etc.). Official communication should be enabled through DMS (Document management system) software in which the business logic of the process should be embedded or at least through process display BPMN (Business Process Modeling Notation) diagrams to enable users to indicate and track which step a particular document and accompanying communication refers to. For informal communication, it is desirable to take place within the DMS software. Still, it is not necessary, i.e., it is possible through a separate communication software platform (if possible, by connecting the communication to the object defined in the DMS software via a unique case ID). For both types of communication, the systems must be common to the entire city system (administrative departments of the city, city companies and institutions). Special attention should be paid to the simplicity of communication because otherwise (especially for informal communication), employees of the city system will resort to simpler  
Figure 5: The requirements of blockchain technology.  
ways of communication (phone call, e-mail, etc.), which is not optimal in the long run, given the digitalization strategy, data tracking, and security.  
The blockchain solution for Smart City is divided into three parts; the first part comprises all city applications such as waste management, healthcare, traffic, and other applications important for city governance, as shown in Figure 6. The second part is network devices (IoT) and communication networks responsible for collecting and data sharing. The final part is the blockchain network for data storage after reaching a consensus among the trusted nodes in the network depending on selected consensus protocols. For each node on the network, smart contracts are defined, and if a node agrees with the rules in smart contract, information is stored in the blockchain [43].  
The solution has numerous heterogeneous devices that are participants in information exchange. These devices should be oracles to ensure trust in exchanged information. A large number of cryptographic keys should be secured to identify each device properly. Keys can be stored locally, in password-protected storage, offline key storage, or on a third-party service, as shown in Table 2.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Approach** & **Description** & **Pros** & **Cons** \\ \hline \multirow{3}{*}{Local storage} & Private keys are stored in a local device with & & \begin{tabular}{c} Prone to online hackers and \\ installation of malicious \\ malware on local devices \\ \end{tabular} \\  & password protection, which can be accessed through & Quick access & \begin{tabular}{c} Prone to online hackers and \\ installation of malicious \\ malware on local devices \\ \end{tabular} \\  & application-based software & & \\ \hline \multirow{2}{*}{Offline storage} & Private keys are secured by storing keys in & \
\begin{tabular}{c} Secure from \\ attack \\ \end{tabular} & No fast access to keys \\  & offline media & & \\ \hline
\begin{tabular}{c} Third party \\ storage \\ \end{tabular} & Services from cloud-neutral providers & Fast and easy & Trust to third party \\ \hline \hline \end{tabular}
\end{table}
Table 2: The key management proposal.  
Figure 6: The blockchain solution for Smart City.