Timestamps and Capability-based Protection in a Distributed Computer Facility

Abstract

This thesis investigates the problems of supporting security requirements and providing protection mechanisms in a distributed computer facility. The nature of the environment necessitates examination of operating systems, data base systems, and computer networks. The capability approach to providing protection in a centralized system is chosen as the foundation for the protection mechanism of the distributed system. The thesis also relies on an interesting approach to the representation of objects in a computer system. An object is represented by a sequence of immutable versions that represent the state of the object over time; each version is the result of an update on the object. This approach to describing objects provides the basis for a flexible definition of the world in which timestamps are naturally associated with every object in the system. The development of a DCF capability mechanism resulted in the following discoveries: Capabilities need not become immediately effective upon their generation. It is not necessary that the object to which access is being authorized exist at the time the capability is generated. And, the revocation of access privileges and the control of capability propagation are not insurmountable problems even in a distributed environment.