By aggregating the essentials and repre-senting them in a structured format, we attempt to provide clarity on thecurrent state of research. In addition, a (non-exhaustive) overview of con-temporary trends in network-based covert channels is given, explainingcommon channels within IP, TCP, ICMP, HTTP and DNS. Lastly, sev-eral implementations were evaluated to gain insight in their efficiency andperformance, and the influences to which they¡¯re prone. We conclude thatthey pose a security issue that needs proper attention when defining andenforcing security policies, and expect more sophisticated covert channelsto appear in the future.
