Searching for a black hole in arbitrary networks: optimal mobile agent protocols
Proceedings of the twenty-first annual symposium on Principles of distributed computing
Mobile Search for a Black Hole in an Anonymous Ring
DISC '01 Proceedings of the 15th International Conference on Distributed Computing
Mobile Agent Security - Issues and Directions
IS&N '99 Proceedings of the 6th International Conference on Intelligence and Services in Networks: Paving the Way for an Open Service Market
Time Limited Blackbox Security: Protecting Mobile Agents From Malicious Hosts
Mobile Agents and Security
Protecting Mobile Agents Against Malicious Hosts
Mobile Agents and Security
A Framework to Protect Mobile Agents by Using Reference States
ICDCS '00 Proceedings of the The 20th International Conference on Distributed Computing Systems ( ICDCS 2000)
Complexity of Searching for a Black Hole
Fundamenta Informaticae
Searching for a black hole in tree networks
OPODIS'04 Proceedings of the 8th international conference on Principles of Distributed Systems
Hardness and approximation results for Black Hole Search in arbitrary networks
Theoretical Computer Science
Locating and Repairing Faults in a Network with Mobile Agents
SIROCCO '08 Proceedings of the 15th international colloquium on Structural Information and Communication Complexity
Searching for black-hole faults in a network using multiple agents
OPODIS'06 Proceedings of the 10th international conference on Principles of Distributed Systems
Distributed security algorithms by mobile agents
ICDCN'06 Proceedings of the 8th international conference on Distributed Computing and Networking
Black hole search in asynchronous rings using tokens
CIAC'06 Proceedings of the 6th Italian conference on Algorithms and Complexity
Approximation bounds for black hole search problems
OPODIS'05 Proceedings of the 9th international conference on Principles of Distributed Systems
Black hole search in directed graphs
SIROCCO'09 Proceedings of the 16th international conference on Structural Information and Communication Complexity
Locating a black hole in an un-oriented ring using tokens: the case of scattered agents
Euro-Par'07 Proceedings of the 13th international Euro-Par conference on Parallel Processing
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A black hole is a highly harmful stationary process residing in a node of a network and destroying all mobile agents visiting the node, without leaving any trace. We consider the task of locating a black hole in a (partially) synchronous arbitrary network, assuming an upper bound on the time of any edge traversal by an agent. For a given graph and a given starting node we are interested in finding the fastest possible Black Hole Search by two agents (the minimum number of agents capable to identify a black hole). We prove that this problem is NP-hard in arbitrary graphs, thus solving an open problem stated in [2]. We also give a 7/2-approximation algorithm, thus improving on the 4-approximation scheme observed in [2]. Our approach is to explore the given input graph via some spanning tree. Even if it represents a very natural technique, we prove that this approach cannot achieve an approximation ratio better than 3/2.