BALANCING PRIVACY, PRECISION AND PERFORMANCE IN DISTRIBUTED SYSTEMS

Privacy, Precision, and Performance (3Ps) are three fundamental design objectives in distributed systems. However, these properties tend to compete with one another and are not considered absolute properties or functions. They must be defined and justified in terms of a system, its resources, stakeholder concerns, and the security threat model. To date, distributed systems research has only considered the trade-offs of balancing privacy, precision, and performance in a pairwise fashion. However, this dissertation formally explores the space of trade-offs among all 3Ps by examining three representative classes of distributed systems, namely Wireless Sensor Networks (WSNs), cloud systems, and Data Stream Management Systems (DSMSs). These representative systems support large part of the modern and mission-critical distributed systems. WSNs are real-time systems characterized by unreliable network interconnections and highly constrained computational and power resources. The dissertation proposes a privacy-preserving in-network aggregation protocol for WSNs demonstrating that the 3Ps could be navigated by adopting the appropriate algorithms and cryptographic techniques that are not prohibitively expensive. Next, the dissertation highlights the privacy and precision issues that arise in cloud databases due to the eventual consistency models of the cloud. To address these issues, consistency enforcement techniques across cloud servers are proposed and the trade-offs between 3Ps are discussed to help guide cloud database users on how to balance these properties. Lastly, the 3Ps properties are examined in DSMSs which are characterized by high volumes of unbounded input data streams and strict real-time processing constraints. Within this system, the 3Ps are balanced through a proposed simple and efficient technique that applies access control policies over shared operator networks to achieve privacy and precision without sacrificing the systems performance. Despite that in this dissertation, it was shown that, with the right set of protocols and algorithms, the desirable 3P properties can co-exist in a balanced way in well-established distributed systems, this dissertation is promoting the use of the new 3Ps-by-design concept. This concept is meant to encourage distributed systems designers to proactively consider the interplay among the 3Ps from the initial stages of the systems design lifecycle rather than identifying them as add-on properties to systems

A robust cooperative spectrum sensing method against faulty nodes in CWSNs

International audienceCognitive wireless sensor networks (CWSNs) become promising infrastructures, which can improve spectrum utilization of traditional wireless sensor networks (WSNs). For cognition in WSNs, spectrum sensing is one of the most crucial function to prevent hazardous interferences with the licensed users and to identify available spectrum for improving the spectrum utilization. In this paper, we propose a robust cooperativespectrum sensing method based on Dempster-Shafer (D-S) theory. Firstly, taking into account the increase of transmitted data with the rise of the number of sensor nodes and the power limitation of nodes, we propose to adapt the D-S theory to the binary hypothesis test at the local sensing sensor node, in order to reduce the amount of control data to be transmitted. Secondly, we consider that some cognitive nodes may not work as expected. Hence, facing this problem of faulty nodes in CWSNs, we propose an evaluation method which considers simultaneously the sensornode reliability and the mutually supportive degree among different sensor nodes to support adapted decision. Simulation results show that the proposed method allows to improve significantly the detection performance compared to other techniques, even in presence of faulty nodes