  Several approaches have been used to assess the performance of cyberphysical
systems and their exposure to various types of risks. Such assessments have
become increasingly important as autonomous attackers ramp up the frequency,
duration and intensity of threats while autonomous agents have the potential to
respond to cyber-attacks with unprecedented speed and scale. However, most
assessment approaches have limitations with respect to measuring cyber
resilience, or the ability of systems to absorb, recover from, and adapt to
cyberattacks. In this paper, we provide an overview of several common
approaches, discuss practical challenges and propose research directions for
the development of effective cyber resilience measures.
