In fully self-organized MANETs, nodes are naturally reluctant to spend their precious resources forwarding other nodes' packets and are therefore liable to exhibit selfish or sometimes malicious behaviour. This selfishness could potentially lead to network partitioning and network performance degradation. Cooperation enforcement schemes, such as reputation and trust based schemes have been proposed to counteract the issue of selfishness. The sole purpose of these schemes is to ensure selfish nodes bear the consequences of their bad actions. However, malicious nodes can exploit mobility and free identities available to breach the security of these systems and escape punishment or detection. Firstly, in the case of mobility, a malicious node can gain benefit even after having been detected by a reputation-based system, by interacting directly with its source or destination nodes. Secondly, since the lack of infrastructure in MANETs does not suit centralized identity management or centralized Trusted Third Parties, nodes can create zero-cost identities without any restrictions. As a result, a selfish node can easily escape the consequences of whatever misbehaviour it has performed by simply changing identity to clear all its bad history, known as whitewashing. Hence, this makes it difficult to hold malicious nodes accountable for their actions. Finally, a malicious node can concurrently create and control more than one virtual identity to launch an attack, called a Sybil attack. In the context of reputation-based schemes, a Sybil attacker can disrupt the detection accuracy by defaming other good nodes, self-promoting itself or exchanging bogus positive recommendations about one of its quarantined identities. This thesis explores two aspects of direct interactions (DIs), i. e. Dis as a selfish nodes' strategy and Dis produced by inappropriate simulation parameters. In the latter case DIs cause confusion in the results evaluation of reputation-based schemes. We propose a method that uses the service contribution and consumption information to discourage selfish nodes that try to increase their benefit through DIs. We also propose methods that categorize nodes' benefits in order to mitigate the confusion caused in the results evaluation. A novel layered security approach is proposed using proactive and reactive paradigms to counteract whitewashing and Sybil attacks. The proactive paradigm is aimed at removing the advantages that whitewashing can provide by enforcing a non-monetary entry fee per new identity, in the form of cooperation in the network. The results show that this method deters these attackers by reducing their benefits in the network. In the reactive case, we propose a lightweight approach to detect new identities of whitewashers and Sybil attackers on the MAC layer using the 802.11 protocol without using any extra hardware. The experiments show that a signal strength based threshold exists which can help us detect Sybil and whitewashers' identities. Through the help of extensive simulations and real-world testbed experimentations, we are able to demonstrate that our proposed solution detects Sybil or whitewashers' new identities with good accuracy and reduces the benefits of malicious activity even in the presence of mobility.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:543741 |
| Date | January 2011 |
| Creators | Abbas, Sohail |
| Publisher | Liverpool John Moores University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://researchonline.ljmu.ac.uk/6091/ |
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