  Hardware reverse engineering is a universal tool for both legitimate and
illegitimate purposes. On the one hand, it supports confirmation of IP
infringement and detection of circuit malicious manipulations, on the other
hand it provides adversaries with crucial information to plagiarize designs,
infringe on IP, or implant hardware Trojans into a target circuit. Although
reverse engineering is commonplace in practice, the quantification of its
complexity is an unsolved problem to date since both technical and human
factors have to be accounted for. A sophisticated understanding of this
complexity is crucial in order to provide a reasonable threat estimation and to
develop sound countermeasures, i.e. obfuscation transformations of the target
circuit, to mitigate risks for the modern IC landscape. The contribution of our
work is threefold: first, we systematically study the current research branches
related to hardware reverse engineering ranging from decapsulation to
gate-level netlist analysis. Based on our overview, we formulate several open
research questions to scientifically quantify reverse engineering, including
technical and human factors. Second, we survey research on problem solving and
on the acquisition of expertise and discuss its potential to quantify human
factors in reverse engineering. Third, we propose novel directions for future
interdisciplinary research encompassing both technical and psychological
perspectives that hold the promise to holistically capture the complexity of
hardware reverse engineering.
