Research Article DYSSS: A Dynamic and Context-Aware Security System for Shared Sensor Networks Claudio M. de Farias, 1 Luci Pirmez, 1 Luiz F. R. C. Carmo, 1,2 Davidson Boccardo, 2 Flávia C. Delicato, 1 Igor L. dos Santos, 1 Renato Pinheiro, 1 and Rafael O. Costa 1 1 Programa de P´ os-Graduac ¸˜ ao em Inform´ atica, Instituto T´ ercio Pacitti de Aplicac ¸˜ oes e Pesquisas Computacionais, Instituto de Matem´ atica, Universidade Federal do Rio de Janeiro, 21941-901 Rio de Janeiro, RJ, Brazil 2 Instituto Nacional de Metrologia, Qualidade e Tecnologia, 25250-020 Duque de Caxias, RJ, Brazil Correspondence should be addressed to Claudio M. de Farias; cmicelifarias@gmail.com Received 11 June 2015; Accepted 17 September 2015 Academic Editor: Rafaele Gravina Copyright © 2015 Claudio M. de Farias et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In recent years, we have witnessed the emergence of Shared Sensor Networks (SSNs) as a core component of cyber-physical systems for diverse applications. As Wireless Sensor and Actuator Networks (WSANs) design starts shifing from application-specifc platforms to shared system infrastructures, a pressing research challenge is security. In scenarios involving unprotected hostile outdoor areas, SSNs are prone to diferent types of attacks that can compromise reliability, integrity, and availability of the sensor data trafc and sensor lifetime as well. In this work we propose a Dynamic Security System to be applied in the shared sensor network context. Its basic feature is the nodes neighborhood monitoring and collaboration (through the use of the Byzantine algorithm) to identify an attack and enhance security. Te proposed security system is dynamic since it is able to manage the availability, integrity, and confdentiality of multiple applications according to the current execution context. It is also resilient, since it is able to support the continuous network operation even in the presence of malicious or faulty nodes. Its resilience is achieved for the capacity of gathering information from several nodes, thus inferring the countermeasures using context information. 1. Introduction Recent advances in microelectromechanical systems and wireless communication technologies have enabled the build- ing of low-cost and small-sized sensors nodes, which are capable of sensing, processing, and communicating through wireless links. Wireless Sensor Networks (WSNs) are com- posed of tens, hundreds, or even thousands of sensor nodes [1, 2]. Nodes in WSNs commonly rely on nonrechargeable batteries as their energy sources, and the replacement of depleted batteries is not always feasible or desirable. Tere- fore, a major challenge in the design of WSNs is how to save energy in order to extend the network operational lifetime. Wireless Sensor Networks are commonly used to monitor a wide range of environmental variables, such as temperature, humidity, acceleration, and light among others [3]. Tese networks can thus be regarded as the interface between the physical world and the world of electrical/electronic devices, as computers and domestic appliances [4]. WSNs communicate the information collected by their sensing devices through their wireless links, thus enabling interaction between people or computers and the surrounding envi- ronment [5]. Te data gathered by the diferent nodes is transmitted to one or more sink nodes. Sink nodes are devices endowed with high processing power and with no energy constraints. Such nodes act as the entry points for application requests and also as the gathering points of sensor-collected data [1]. Te WSN technology can also encompass the use of wireless actuators, originating the concept of Wireless Sensor and Actuator Networks (WSANs) [5]. Besides the inherent sensing capabilities of the WSNs, the additional Hindawi Publishing Corporation International Journal of Distributed Sensor Networks Volume 2015, Article ID 756863, 9 pages http://dx.doi.org/10.1155/2015/756863