Zero Trust Federation: Sharing Context under User Control towards Zero Trust in Identity Federation

Perimeter models, which provide access control for protecting resources on networks, make authorization decisions using the source network of access requests as one of critical factors. However, such models are problematic because once a network is intruded, the attacker gains access to all of its resources. To overcome the above problem, a Zero Trust Network (ZTN) is proposed as a new security model in which access control is performed by authenticating users who request access and then authorizing such requests using various information about users and devices called contexts. To correctly make authorization decisions, this model must take a large amount of various contexts into account. However, in some cases, an access control mechanism cannot collect enough context to make decisions, e.g., when an organization that enforces access control joins the identity federation and uses systems operated by other organizations. This is because the contexts collected using the systems are stored in individual systems and no federation exists for sharing contexts. In this study, we propose the concept of a Zero Trust Federation (ZTF), which applies the concept of ZTN under the identity federation, and a method for sharing context among systems of organizations. Since context is sensitive to user privacy, we also propose a mechanism for sharing contexts under user control. We also verify context sharing by implementing a ZTF prototype.