  The increased connectivity and potential insider threats make traditional
network defense vulnerable. Instead of assuming that everything behind the
security perimeter is safe, the zero-trust security model verifies every
incoming request before granting access. This chapter draws attention to the
cyber resilience within the zero-trust model. We introduce the evolution from
traditional perimeter-based security to zero trust and discuss their
difference. Two key elements of the zero-trust engine are trust evaluation (TE)
and policy engine (PE). We introduce the design of the two components and
discuss how their interplay would contribute to cyber resilience. Dynamic game
theory and learning are applied as quantitative approaches to achieve automated
zero-trust cyber resilience. Several case studies and implementations are
introduced to illustrate the benefits of such a security model.
