Algorithms for testing security in graphs

W niniejszym artykule przedstawiamy metodę weryfikowania bezpieczeństwa zbioru w grafie, dającą wysokie prawdopodobieństwo poprawnej weryfikacji. Problemem jest określenie, czy dla danego grafu G oraz podzbioru S zbioru wierzchołków tego grafu zbiór S jest bezpieczny, to znaczy każdy jego podzbiór X spełnia warunek: |N[X] ∩ S| ≥ |N[X] \ S|, gdzie N[X] jest domkniętym sąsiedztwem zbioru X w grafie G. Zaprojektowaliśmy pseudotester o wielomianowej złożoności obliczeniowej dla decyzyjnego problemubezpieczeństwa zbioru w grafie wykorzystując m.in. koncepcję symulowanego wyżarzania. Wykonaliśmy testy dla grafów, w których podgraf indukowany przez zbiór S jest drzewem lub grafem ograniczonego stopnia (przez 3 oraz 4). Z uwagi na coNP-zupełność problemu bezpieczeństwa zaproponowane przez nas podejście jest uogólnieniem koncepcji testowania własności znanej z literatury. In this paper we propose new algorithmic methods giving with a high probability the correct answer to the decision problem of security in graphs. For a given graph G and a subset S of a vertex set of G we have to decide whether S is secure, i.e. every subset X of S fulfils the condition: |N[X] S| |N[X] \ S|, where N[X] is a closed neighbourhood of X in graph G. We constructed a polynomial time property pseudotester based on the heuristic using simulated annealing and tested it on graphs with induced small subgraphs G[S] being trees or graphs with a bounded degree (by 3 or 4). Our approach is a generalization of the concept of property testers known from the subjectliterature, but we applied our concepts to the coNP-complete problem

Guarding Networks Through Heterogeneous Mobile Guards

In this article, the issue of guarding multi-agent systems against a sequence of intruder attacks through mobile heterogeneous guards (guards with different ranges) is discussed. The article makes use of graph theoretic abstractions of such systems in which agents are the nodes of a graph and edges represent interconnections between agents. Guards represent specialized mobile agents on specific nodes with capabilities to successfully detect and respond to an attack within their guarding range. Using this abstraction, the article addresses the problem in the context of eternal security problem in graphs. Eternal security refers to securing all the nodes in a graph against an infinite sequence of intruder attacks by a certain minimum number of guards. This paper makes use of heterogeneous guards and addresses all the components of the eternal security problem including the number of guards, their deployment and movement strategies. In the proposed solution, a graph is decomposed into clusters and a guard with appropriate range is then assigned to each cluster. These guards ensure that all nodes within their corresponding cluster are being protected at all times, thereby achieving the eternal security in the graph.Comment: American Control Conference, Chicago, IL, 201

Protecting a Graph with Mobile Guards

Mobile guards on the vertices of a graph are used to defend it against attacks on either its vertices or its edges. Various models for this problem have been proposed. In this survey we describe a number of these models with particular attention to the case when the attack sequence is infinitely long and the guards must induce some particular configuration before each attack, such as a dominating set or a vertex cover. Results from the literature concerning the number of guards needed to successfully defend a graph in each of these problems are surveyed.Comment: 29 pages, two figures, surve

Characterizations and algorithms for generalized Cops and Robbers games

We propose a definition of generalized Cops and Robbers games where there are two players, the Pursuer and the Evader, who each move via prescribed rules. If the Pursuer can ensure that the game enters into a fixed set of final positions, then the Pursuer wins; otherwise, the Evader wins. A relational characterization of the games where the Pursuer wins is provided. A precise formula is given for the length of the game, along with an algorithm for computing if the Pursuer has a winning strategy whose complexity is a function of the parameters of the game. For games where the position of one player does not affect the available moves of he other, a vertex elimination ordering characterization, analogous to a cop-win ordering, is given for when the Pursuer has a winning strategy

Disjoint Dominating Sets with a Perfect Matching

In this paper, we consider dominating sets $D$ and $D'$ such that $D$ and $D'$ are disjoint and there exists a perfect matching between them. Let $DD_{\textrm{m}}(G)$ denote the cardinality of smallest such sets $D, D'$ in $G$ (provided they exist, otherwise $DD_{\textrm{m}}(G) = \infty$). This concept was introduced in [Klostermeyer et al., Theory and Application of Graphs, 2017] in the context of studying a certain graph protection problem. We characterize the trees $T$ for which $DD_{\textrm{m}}(T)$ equals a certain graph protection parameter and for which $DD_{\textrm{m}}(T) = \alpha(T)$, where $\alpha(G)$ is the independence number of $G$. We also further study this parameter in graph products, e.g., by giving bounds for grid graphs, and in graphs of small independence number

Securing Multiagent Systems Against a Sequence of Intruder Attacks

Presented at the 2012 American Control Conference, June 27-29, Montréal, Canada.In this paper, we discuss the issue of security in multiagent systems in the context of their underlying graph structure that models the interconnections among agents. In particular, we investigate the minimum number of guards required to counter an infinite sequence of intruder attacks with a given sensing and response range of an individual guard. We relate this problem of eternal security in graphs to the domination theory in graphs, providing tight bounds on the number of guards required along with schemes for securing a multiagent system over a graph