Is Trust Misplaced? A Zero-Trust Survey

Information technology (IT) security has been, and largely is, based on compartmentalization. To implement compartmentalization, system access privileges are granted depending on the topological location of systems, grouped into perimeters, with network mechanisms (firewalls, VLANs, ...) enforcing isolation between perimeters, thus implicitly trusting systems based on their location. However, history has shown that such trust is misplaced. This has led to the emergence of an alternative paradigm, called zero trust. After contextualizing the history of IT and the emergence of zero trust for securing networks, this article presents a taxonomy of zero trust models and architectures, summarizing the goals and core principles of zero trust. Furthermore, an in-depth description of state-of-the-art technologies and methods, for transforming perimeter-based architectures to mature zero-trust architectures, is provided. This article presents a formalization of zero trust and of optimal zero-trust architectures, to which traditional architectures migrate, as well as a method for positioning migrating architectures relative to this ideal of zero trust, with as purpose of enabling a clearer understanding of the benefits and risks induced by a migration to zero trust. Finally, this article analyses the benefits, and drawbacks, of zero trust, focusing on the security properties granted by zero trust, as well as the vulnerabilities introduced.