Authentication in a distributed system during partition

ABSTRACT

In a distributed system data cached at a workstation are usually regarded as hints whose currency is not guaranteed. Guaranteed values are obtained from a network file server, which also looks after such things as back-up. In practice decisions may be taken based on cached values which are not known to be current. In a system with replicated data this principle may be followed to increase availability during partition. In particular it may be applied to the system's authentication database in order to allow access to a workstation even if no network authentication service is available. Provided that simple precautions are followed control data stored on the local disc may be used to enforce security when the network is down. The control data may not be current, and it may be prudent to offer restricted facilities in such circumstances. This is an example of the general dilemma that users face when the quality of information is known to be poor.