Group-Centric Secure Information-Sharing Models for Isolated Groups

Group-Centric Secure Information Sharing (g-SIS) envisions bringing users and objects together in a group to facilitate agile sharing of information brought in from external sources as well as creation of new information within the group. We expect g-SIS to be orthogonal and complementary to authorization systems deployed within participating organizations. The metaphors “secure meeting room” and “subscription service” characterize the g-SIS approach. The focus of this article is on developing the foundations of isolated g-SIS models. Groups are isolated in the sense that membership of a user or an object in a group does not affect their authorizations in other groups. Present contributions include the following: formal specification of core properties that at once help to characterize the family of g-SIS models and provide a “sanity check” for full policy specifications; informal discussion of policy design decisions that differentiate g-SIS policies from one another with respect to the authorization semantics of group operations; formalization and verification of a specific member of the family of g-SIS models; demonstration that the core properties are logically consistent and mutually independent; and identification of several directions for future extensions. The formalized specification is highly abstract. Besides certain well-formedness requirements that specify, for instance, a user cannot leave a group unless she is a member, it constrains only whether user-level read and write operations are authorized and it does so solely in terms of the history of group operations; join and leave for users and add, create, and remove for objects. This makes temporal logic one of the few formalisms in which the specification can be clearly and concisely expressed. The specification serves as a reference point that is the first step in deriving authorization-system component specifications from which a programmer with little security expertise could implement a high-assurance enforcement system for the specified policy.