Although Wireless Sensor Networks (WSNs) have found a niche in numerous applications, they are constrained by numerous factors. One of these important factors is security in WSNs. There are various types of security attacks that WSNs are susceptible to. The focus of this study is centred on Sybil attacks, a denial of service attack. In this type of attack, rogue nodes impersonate valid nodes by falsely claiming to possess authentic identities, thereby rendering numerous core WSN operations ineffective. The diverse nature of existing solutions poses a difficult problem for system engineers wanting to employ a best fit countermeasure. This problem is the largely unanswered question posed to all system engineers and developers alike whose goal is to design/develop a secure WSN. Resolving this dilemma proves to be quite a fascinating task, since there are numerous factors to consider and more especially one cannot assume that every application is affected by all identified factors. A framework methodology presented in this study addresses the abovementioned challenges by evaluating countermeasure effectiveness based on theoretical and practical security factors. Furthermore, a process is outlined to determine the application’s engineering requirements and the framework also suggests what security components the system engineer ought to incorporate into the application, depending on the application’s risk profile. The framework then numerically aligns these considerations, ensuring an accurate and fairly unbiased best fit countermeasure selection. Although the framework concentrates on Sybil countermeasures, the methodology can be applied to other classes of countermeasures since it answers the question of how to objectively study and compare security mechanisms that are both diverse and intended for different application environments. The report documents the design and development of a comparative framework that can be used to evaluate countermeasures against Sybil attacks in wireless sensor networks based on various criteria that will be discussed in detail. This report looks briefly at the aims and description of the research. Following this, a literature survey on the body of knowledge concerning WSN security and a discussion on the proposed methodology of a specific design approach are given. Assumptions and a short list of factors that were considered are then described. Metrics, the taxonomy for WSN countermeasures, the framework and a formal model are developed. Risk analysis and the best fit methodology are also discussed. Finally, the results and recommendations are shown for the research, after which the document is concluded. / Dissertation (MEng)--University of Pretoria, 2011. / Electrical, Electronic and Computer Engineering / unrestricted