International Journal of Computer Applications (0975 – 8887) Volume 88 – No.15, February 2014 13 Cooperative Gray Hole Attack Discovery and Elimination using Credit based Technique in MANET Deepali A. Lokare Sinhgad Institute of Technology, Lonavala, Pune A.M Kanthe Faculty of Electrical Engineering and Computing, University of Zagreb, Croatia Dina Simunic Faculty of Electrical Engineering and Computing, University of Zagreb, Croatia ABSTRACT A MANET (Mobile Ad-hoc Network) is a network of mobile devices in a self-configuring and infrastructure less environment. The devices in MANET are linked by wireless medium. There are big chances of attacks in MANET due to its natural features including dynamically changing network topology, open medium, no centralized monitoring and management point. There is no assurance of attack free communication. The malicious node(s) causes dropping and forwarding only selective packets are called as gray hole. So, the security solution must be developed to address the protection of data and route. In this paper we attempted to mitigate the gray hole attack and proposes a credit based approach based on Ad-hoc On Demand Distance Vector (AODV) routing protocol. In the proposed and implemented method, we used credit value measurement for the detection of cooperative gray hole attack. This paper shows the technique which is capable of finding chains of cooperating gray hole nodes which drop a major part of communication. The paper shows the result based on varying density, pause time and mobility. Keywords Mobile Ad-hoc Network (MANET), Packet forwarding misbehavior, Cooperative gray hole attack, Security, AODV 1. INTRODUCTION A mobile ad-hoc network (MANET) is a collection of wireless nodes in infrastructure less networks with no central control. MANET can set up dynamically anytime, anywhere without using any pre-existing infrastructure of a network. The media used for communication is wireless and unreliable. Also, the nodes are free to move at random and they act as router at the same time. Hence the transmission of packets was using multi-hop packet forwarding. This sort of network is well suitable for many applications inclusive of military operations, emergency relief and terrorism response. The mobile ad-hoc networks are vulnerable to different types of attacks because no centralized access control, nodes behavior (nodes are free to leave, join and move inside the network) and partial resources. The attacks are various types of DoS (Denial of Service) attacks [1] [2]. Among these attacks, one of the most important security issues is the safety of network layer from different active and dynamic routing attacks. The attack includes gray hole attack and black hole attack. The basic description of MANET causes some major issues for MANET including security, mobility management, service discovery, IP addresses, radio interference, protocols of routing, bandwidth constraints and power constraints, Quality of Services (QoS), etc. [3]. Intrusion avoidance techniques such as strong authentication and redundant transmission can be used to improve the security of an ad- hoc network. However, these techniques can deal with only a subset of the threats. Moreover, they are expensive to implement. The most vital concern in MANET is Security for basic functionality of the network. The basic services like reliability, privacy and network services are achieved by assuring that security issues have been met. Mostly MANET undergoes different security attacks because of its open medium, dynamic changes in topology, no central monitoring and management, and no clear protection mechanism. These factors have changed the conflict zone situation for the MANET beside the security threats [4] The MANET is vulnerable to many active and passive attacks because of the distinctive and challenging features including no central control, unbounded boundaries (nodes are free to roam) and partial resources. Hence important and the first security issue is protection of network layer from different routing attacks. Today main threat category in MANET is a DoS attack. Also, the attacks are routing attacks. The routing attacks are classified as a Black hole attack and gray hole attack that show signs of packet forwarding misbehavior. The malicious node (black hole) replies to the each and every attack route request by incorrectly claiming that it leads to destination and has a fresh enough route to the destination. This is called black hole attack. In this fashion, all traffic is forwarded to the black hole node which then leaves them all. Whereas, there is a change in the case of gray hole attack. In gray hole attack, the malicious node (gray hole) acted honest sometimes and dishonest on the other time. During the route discovery process, this nodes act as honest node then once source believes, it silently drops some of data packets. The packets are dropped partially and not completely. The behavior of the gray hole node is unpredictable. A node behaves as honest node and sometimes malicious. Hence, the gray hole attack is an extension of the black hole attack and its detection tougher than black hole attack. However, both attacks are mainly targeted on route discovery process disturbance and degrading network’s performance. 1.1. Black Hole Attack This is a type of DoS attack. In route discovery, the node (black hole) responds to source’s request with implying shortest path to the destination. In reality it is not the case. The source believes and sends the data packet through this black hole node and in turn, this black hole node drops all data packets. Due to this attack, the performance of network