An access control mechanism based on Boolean expression evaluation is presented. This mechanism allows the implementation of customer-specified, rather than vendor-specified, security policies. The mechanism makes it possible to easily implement such conventional mechanisms as access control lists, named access control lists, user groups, user attributes, user capability lists, and user roles. Additional access restrictions based on time, day, date, location, load average, or any customer-supplied function can be incorporated into access decisions. This mechanism can directly express Clark-Wilson triples, and it can easily implement policies that are difficult or impossible to implement using the Bell-LaPadula model.>

A new type of system architecture is described that uses both duplex ct)mmunication and wide-area simplex commtmication to implement a single service.A working community inlbrmation system based on this architecture is discussed fiom a systems perspective, with an emphasis on the unique way in which processing is distributed among a confederation of shared servers and private personal systems.In the community infimnation system, each personal system maintains a local, user-defined subset of the databases stored on the shared servers.I)atabase updates are transnfitted to the personal systems via a broadcast packet radio system.This design allows many queries to be processed completely at users' personal machines, and thus reduces the reliance on shared servers.A unifying design principle is that the system is seen as a collection of independent shared and personal databascs, as opposed to a single monolithic database.Query routing is used to hide the system's division into component databases from a user.

A problem with conflicting goals of anonymity and authentication is defined and a cryptographic protocol that solves the problem is presented. The protocol uses an authentication scheme that provides the desired degree of anonymity and authentication. Fake transactions are used to detect active attackers, and to camouflage information that cannot be hidden cryptographically.