Guardians for Ambient-Based Monitoring

Abstract

In the Mobile Ambients of Cardelli and Gordon an ambient is a unit for mobility, which may contain processes (data) and sub-ambients. Since the seminal work of Cardelli and Gordon, several ambient-based calculi have been proposed (Seal, Box-π, Safe Ambients, Secure Safe Ambients, Boxed Ambients), mainly for supporting security. At the operational level these (box- and) ambient-based calculi differ only in the capabilities of processes. We propose a way of extending ambient-based calculi, which embodies two principles: an ambient is a unit for monitoring and coordination, the name of an ambient determines its (monitoring and coordination) policy. More specifically, to each ambient we attach a guardian, which monitors the activity of sub-components (i.e. processes and sub-ambients) and the interaction with the external environment. In our proposal, guardians and processes play a dual role: guardians are centralized entities monitoring and inhibiting actions, while processes are decentralized entities performing actions. We exemplify the use of guardians for enforcing security properties.