**6. Discussion**

In this paper, we introduce a smart city as a scenario and use Kolmogorov entropy to calculate the degree of chaos of cryptocurrency and smart city. Smart cities applying cryptocurrency can introduce monetary entropy, which may be one of the future research directions. In addition, smart cities can also use entropy to measure the development of the whole urban system. The following are the main development directions of smart cities.

The construction of smart cities is the development direction of major cities in China in these years, along with the rapid development of information and communication technology (ICT) such as artificial intelligence, 5G, blockchain and Internet of Things, which make the technical means of building smart cities more and more perfect, but at the same time, cities generate a large amount of data and huge data transmission tasks, which leads to the problem of information security, and blockchain technology can rebuild trust in society and solve the sharing problem. However, the application of blockchain technology in smart cities is a difficult system project, requiring the construction of a secure and credible smart city data infrastructure, a city-level multi-level blockchain public service platform, and a breakthrough with a focus on government service innovation to promote the gradual implementation of blockchain applications. In the subsequent development of blockchain technology applications in smart cities, importance should be attached to the construction of blockchain underlying architecture and infrastructure, putting the building of blockchain basic service platforms in the first place, deep integration with technologies such as big data, artificial intelligence and the Internet of Things, and further improvement of regulatory and standard systems. What we want to solve the openness, exchange, integration, sharing and security of data resources that are isolated and segregated because of category, industry, sector and geography. Based on the analysis of blockchain technology in Part II III, as shown in Figure 4, we can divide the development of smart cities into four directions—people's livelihood services, urban governance, industrial economy and ecological livability.
