# IoT-Enabled Smart Sustainable Cities: Challenges and Approaches
## 3 Improving the Sustainability of a Smart City
### Legality and Security  
As already mentioned for other aspects, although cities are trying to become smarter by adopting different solutions, smart city applications highlight a series of challenges and concerns in terms of privacy and security, as city operators should be able to defend the generated or collected information (regarding all the entities involved in the life of the city itself) from unauthorized access, modification, inspection, disclosure, and disruption [4]. Therefore, as shown in Figure 7, privacy and security requirements underlying the overall infrastructure, which the city lives on, including availability, integrity, confidentiality, access control, and non-repudiation, should be handled and satisfied [90]. As widely known, securing a smart city is not easy and faces a set of challenges which should be carefully considered. On one hand, a smart city collects (from IoT-oriented on-field sensing nodes) privacy-sensitive and granular-scale data regarding the environment and people's lives, while, on the other hand, produces estimations and takes decisions based on these information, which, in a certain way, impacts people's lives. This is why privacy and security issues become challenging and should be carefully considered, especially in the light of modern IoT-oriented processing mechanisms, and enhanced and distributed Fog/Edge/Cloud Computing-based data analysis infrastructures. Looking in detail at these issue, a _first_ vulnerability is related to privacy leakage and data inferring by external attackers, operated when private data (e.g., regarding citizen's identity and location in a certain time instant, health condition, biomedical information inferred from intelligent surveillance)are collected, transmitted, and processed. As a solution, off-the-shelf privacy and security techniques can be applied [91; 92], as in the case of surveillance systems capturing user-related information (e.g., a security camera, used to detect abnormal events or theft) [92; 93; 94]. A _second_ vulnerability is related to the fact that, as a city (and, of course, a smart city) has a two-way control flow--sensors, to sense physical quantities, and actuators, to act on the environment on the basis of the processed data, this flow should be protected against attacks of heterogeneous nature. Illustrative attacks are malicious data injection, spoofing attacks, Denial of service (DoS) attacks, and Distributed DoS (DDoS) attacks. Moreover, operators should care about third-party components and plug-ins, as these are often the preferred targets of the attackers [95]. With regard to intelligent healthcare, especially with reference to the COVID-19 pandemic experienced all around the world in 2020, a smart city could rely on the technology to counteract the diffusion of the virus with innovative solutions. If an old-fashioned prevention approach suggests to isolate susceptible people for a certain period, but not considering the possible negative impacts, such as panic or anxiety among the society, economic loss of the isolated people, and massive healthcare expense, then the fusion of data gathered from heterogeneous sources (e.g., social networks, real-time health monitoring systems, etc.) would allow to obtain better results [96; 97]. In this context, IoT could support the implementation of an \"Internet of People\" platform. Another example could be related to the energy management in citizens' houses. In this case, a smart city may target an intelligent energy billing and invoicing through the deployment of a smart grid infrastructure, composed of a multitude of domestic smart meters. Although this may provide several benefits, as highlighted in Section 3.7, various attacks can be attempted to perform malicious actions, such a tampering with smart meter records, forwarding altered data to the grid's control center, and introducing intrusive and unauthorized smart meters, trying to steal sensitive data.