Table 6.

The general requirements of fog-based CAAC mechanism.

Requirement	Description
R1	How to capture and derive the relevant contextual conditions from the IoT, fog and cloud environments? Thus, there is a need for a generic context model to capture and represent relevant contextual conditions using information provided through IoT devices and the associated fog and cloud environments.
R2	How to effectively specify the context-aware access control policies to manage and control data from distributed cloud sources by means of reducing computational overheads? Towards this goal, we can model a single set of access control policies instead of multiple sets of policies for different data sources.
R3	In order to reduce the overheads, how to build a global data model to map the identical attributes (e.g., the contextual conditions) from the relevant data sources and apply the same set of policy in the intermediary fog layer for accessing data from multiple sources?
R4	Focusing on the privacy requirements of the multiple stakeholders, how the end-users can prevent unauthorized entities and can ensure the privileges to access only certain information except sensitive and personally identifiable information?
R5	In order to limit the permissions to data from multiple cloud centres and achieve trust among all peers (e.g., users and other stakeholders), how to build an appropriate data sharing mechanism for all the entities involved, like IoT devices, fog servers and cloud data centres.