Capture of an intruder by mobile agents

Abstract

Consider a team of mobile software agents deployed to capture a (possibly hostile) intruder in a network. All agents, including the intruder move along the network links; the intruder could be arbitrarily fast, and aware of the positions of all the agents. The problem is to design the agents' strategy for capturing the intruder. The main efficiency parameter is the size of the team. This is an instance of the well known graph-searching problem whose many variants have been extensively studied in the literature. In all existing solutions, and in all the variants of the problem, it is assumed that agents can be removed from their current location and placed in another network site arbitrarily and at any time. As a consequence, the existing optimal strategies cannot be employed in situations for which agents cannot access the network at any point, or cannot "jump" across the network, or cannot reach an arbitrary point of the network via an internal travel through insecure zones. This motivates the contiguous search problem in which agents cannot be removed from the network, and clear links must form a connected sub-network at any time, providing safety of movements. This new problem is NP-complete in general. We study it for tree networks, and we consider its more general version, the weighted case, which arises naturally when considering networks whose nodes and links are of different nature and thus require a different number of agents to be explored. We give a linear-time algorithm that computes, for any tree T , the minimum number of agents to capture the intruder, and the corresponding search strategy. Beside its optimality in time, our algorithm is naturally distributed:

Secure Upgrade of Hardware Security Modules in Bank Networks

“…The CMD problem [3]. We consider an initially contaminated network that has to be decontaminated by a set of agents (or searchers) arbitrarily moving inside the network.…”

“…The problem of finding an optimal strategy has been studied in some specific topologies such as trees [3]. In the same work it is also proved that, for trees, a non-monotone solution, i.e., allowing re-contamination of nodes, would not reduce the optimal number of required agents.…”

“…As we have proved in the previous section, in this case this problem is equivalent to the CMD problem where agents are seen as borderline HSMs. We thus slightly modify the algorithm presented in [3] in order to solve our problem.…”

“…We formally state the HSM upgrading problem and we prove that, when only one technician is present, it is strictly related to the Connected Monotone Decontamination (CMD) problem [3], where a team of agents aims at decontaminating a graph and capturing an intruder. The analogy is that decontaminated nodes should never be directly in contact with contaminated ones to avoid the intruder re-contaminating them, thus some agents must stay on the borderlines to 'guard' the decontaminated subnetwork.…”

Multiple Agents RendezVous in a Ring in Spite of a Black Hole

“…The coordination of the agents necessary to perform these operations is not necessarily simple or easy to achieve. In fact, the computational problems related to these operations are definitely non trivial, and a great deal of theoretical research is devoted to the study of conditions for the solvability of these problems and to the discovery of efficient algorithmic solutions; e.g., see [4,5,6,15].…”