  Diversity-based security approaches have been studied for several decades
since the 1970's. The concept of diversity-by-design emerged in the 1980's and,
since then, diversity-based system design research has been explored to build
more secure and dependable systems. In this work, we are particularly
interested in providing an in-depth, comprehensive survey of existing
diversity-based approaches, insights, and future work directions for those who
want to conduct research on developing secure and dependable cyber-physical
systems (CPSs) using diversity as a system design feature. To be specific, this
survey paper provides: (i) The common concept of diversity based on a
multidisciplinary study of diversity from nine different fields along with the
historical evolution of diversity-by-design for security; (ii) The design
principles of diversity-based approaches; (iii) The key benefits and caveats of
using diversity-by-design; (iv) The key concerns of CPS environments in
introducing diversity-by-design; (v) A variety of existing diversity-based
approaches based on five different classifications; (vi) The types of attacks
mitigated by existing diversity-based approaches; (vii) The overall trends of
evaluation methodologies used in diversity-based approaches, in terms of
metrics, datasets, and testbeds; and (viii) The insights, lessons, and gaps
identified from this extensive survey.
