# Privacy and Security in Cognitive Cities: A Systematic Review
## 4 Discussion
### Privacy and Security Are Entangled  
Several privacy enhancing technologies can be applied in the sensing layer of the city hardware infrastructure. In fact, a framework for a comprehensive view of privacy could be envisaged, inspired by a 5-dimensional model for privacy in smart cities [17], namely: identity privacy (using pseudonyms to prevent the disclosure of citizens' identity), query privacy (preserving the privacy of the queries made by citizens to services), location privacy (guaranteeing the exact physical location of citizens is preserved), footprint privacy (related to the information that can be inferred from microdata sets), and owner privacy (focused on privacy-aware computation of queries across databases from different entities). PbD principles must be applied in this privacy framework globally. For instance, regarding visibility and transparency, all stakeholders (from local governments and information system managers to cognitive city technology developers) must be subject to independent verification; moreover, respect for user privacy is essential: information about good practices, down-to-earth notices, and user-friendly interfacing with the technology must be developed.  
In this line, end-to-end security is regarded as a linchpin in PbD. This is a serious issue, because privacy and security are completely entangled: if technology fails, then privacy cannot be guaranteed. Therefore, strong built-in security measures are essential. As an example, proposals for trustworthy privacy-aware video surveillance rely on good privacy practices, but also on strong security properties of hardware and softwareinfrastructures [64], and they are the current subject of study of European projects such as Goodbrother (European Cooperation in Science and Technology--COST Action 19121 [[http://goodbrother.eu](http://goodbrother.eu)]([http://goodbrother.eu](http://goodbrother.eu)), accessed on 12 May 2021).  
Furthermore, given that a cognitive city can be seen as a set of cognitive agents and the _connections_ that the agents make among them, any privacy analysis of the cognitive city must consider the authentication and communication processes among those agents (e.g., requiring mutual authentication). However, the humongous quantity and variety of devices that take part in the cognitive city, makes the authentication and checking of data integrity challenging. Identity and Access Management (IAM) systems must cope with authentication mechanisms providing information security for citizens, information systems, websites, and things. Moreover, queries, use of web services, and any interaction between parties must consider access control. Current public-key authentication mechanisms, based on certificate chains, revocation lists, and multiple-sourced trust, are hard to fit into cognitive cities infrastructures. On the contrary, the single-sourced nature of blockchain makes easier to manage credentials verification and legitimacy.  
To summarize, although PbD is a necessary starting point, it is not enough because serious problems in the cognitive city may arise from the security side.