  This paper addresses the problem of detecting possible intruders in a group
of autonomous robots, which coexist in a shared environment and interact with
each other according to a set of "social behaviors", or common rules. Such
rules specify what actions each robot is allowed to perform in the pursuit of
its individual goals: rules are distributed, i.e. they can evaluated based only
on the state of the individual robot, and on information that can be sensed
directly or through communication with immediate neighbors. We consider
intruders as robots which misbehave, i.e. do not follow the rules, because of
either spontaneous failures or malicious reprogramming. Our goal is to detect
intruders by observing the congruence of their behavior with the social rules
as applied to the current state of the overall system. Moreover, in accordance
with the fully distributed nature of the problem, the detection itself must be
peformed by individual robots, based only on local information. The paper
introduces a formalism that allows to model uniformly a large variety of
possible robot societies. The main contribution consists in the proposal of an
Intrusion Detection System, i.e. a protocol that, under suitabkle conditions,
allows individual robots to detect possible misbehaving robots in their
vicinity, and trigger possible further actions to secure the society. It is
worth noting that the generality of the protocol formalism makes so that local
monitors can be automatically generated once the cooperation rules and the
robot dynamics are specified. The effectiveness of the proposed technique is
shown through application to examples of automated robotic systems.
