## 5 Discussion and Conclusions
Confidentiality grants data access only to individuals and organizations that own these data. During the transfer of data within the different user layers, the main network, storing and processing data in Cloud, Edge, or Fog paradigm, its access is strongly restricted. Encrypting data is a way of achieving confidentiality. Data correctness and consistency is a model of integrity which avoids information being tampered with or modified. Some mechanisms can be used for verifying sent and received data integrity. Only authorized persons are granted access to available data. Thus, availability determines that data must be available anywhere based on established policies. To attain these expectations, various instruments, patterns, methodologies, and mechanisms such as cryptography, encryption, authentication, and others are deployed to the multiple platforms (layers) when data are being transferred and stored. Overall, Cloud, Edge, and Fog paradigms exhibit the same view of providing QoS to customers, but they all have a separate set of features that makes them differ from one another, as we have explained in this work. Notably, the Fog paradigm is designated the most effective and reliable system to better handle the security and privacy challenges encountered. To summarize, even though the Fog paradigm can offer better security and privacy services to end-devices in general, some features of the Fog paradigm, such as decentralization, constraints of resources, homogeneity, and virtualized systems, are vulnerable to security and privacy challenges in comparison to the Cloud paradigm, which is centralized. Due to the absence of standardization regarding countermeasures deployment, highly effective security and privacy mitigation in the Cloud paradigm cannot be implemented straight to the Fog paradigm because of the named features above. Therefore, Fog systems do need innovative countermeasures to address these challenges. Future research should also address new techniques and mechanisms that fit Fog paradigm features and possibly cross-platform countermeasure tools. Hence, they should be suggestions for effective and efficient solutions. The systematic literature review is based on PRISMA guidelines [10]. The publication date range was set from 2017 to 2021. We used the most popular ICT sector databases for research works, such as IEEE, Web of Science, Science Direct, Springer, and Scopus, while not considering pre-prints, duplicates, and gray literature. Later on, we analyzed the titles, abstracts, and keywords of the various academic publications to figure out specific journal articles and other important papers related to security and privacy in Cloud, Edge, and Fog paradigms. The following search query was formulated for reproducibility: \begin{tabular}{|p{341.4 pt}|} \hline TITLE (((cloud OR Edge OR fog) AND computing) AND (security OR privacy)) \\ AND \\ (LIMIT-TO(PUBYEAR, 2021) AND LIMIT-FROM (PUBYEAR, 2017)) AND \\ (LIMIT-TO(SUBJAREA, \"COMP\") OR LIMIT-TO (SUBJAREA, \"ENGI\")) AND \\ (LIMIT-TO(LANGUAGE, \"English\")) AND (LIMIT-TO (PUBSTAGE, \"final\")) \\ \hline \end{tabular}   
Some exclusion criteria were set to narrow the search outcomes during the first screening stage from the paper's titles and abstracts:  
* Not related to security and privacy in Cloud, Edge, and Fog computing;
* Not in English;
* Works with no technical content;
* Purely review papers;
* Full text not available. After applying the exclusion criteria, the selected number of publications was lowered from 1390 to 447. Sixty-one duplicates were found and were taken off the list. The headings of the various articles, their abstracts, and important words of the retained 386 papers were screened, and 187 papers were dismissed since they did not match the exclusion criteria. The number of papers left was 199, and their whole content were thoroughly analyzed. After the additional screening, 122 papers were still rejected since they were unrelated to the topic. **Author Contributions:** Conceptualization, A.O., J.N. ; methodology, A.O.