Sybil attacks against mobile users: friends and foes to the rescue

Collaborative applications for co-located mobile users can be severely disrupted by a sybil attack to the point of being unusable. Existing decentralized defences have largely been designed for peer-to-peer networks but not for mobile networks. That is why we propose a new decentralized defence for portable devices and call it MobID. The idea is that a device manages two small networks in which it stores information about the devices it meets: its network of friends contains honest devices, and its network of foes contains suspicious devices. By reasoning on these two networks, the device is then able to determine whether an unknown individual is carrying out a sybil attack or not. We evaluate the extent to which MobID reduces the number of interactions with sybil attackers and consequently enables collaborative applications.We do so using real mobility and social network data. We also assess computational and communication costs of MobID on mobile phones

Trust and Inventory Replenishment Decision Under Continuous Review System

This thesis examines the impact of inventory manager’ trust on their replenishment decision. We conduct this study in the experimental environment and design an experiment with unknown market demand, local information, and under continuous replenishment review. We also develop a multi-round trust measurement procedure through questionnaires and administer it in the context of a laboratory experiment. To conduct the study, we take the three following steps: First we investigate inventory replenishment decision under continuous review in a decentralized supply chain. Our results show that order time intervals increase along the supply chain. Inventory managers’ replenishment decisions affect their own and the other echelons’ costs. Moreover, we find that wholesaler plays the smoothing role in the decentralized supply chain. Second, we develop a multi-round trust measurement procedure through questionnaires and conduct it in the context of a laboratory experiment. This design allows us to observe inventory managers’ trust in customer and trust in supplier over time. Our results show that trust exist in a decentralized supply chain, with local information, no communication, and no access to the market demand, and trust level varies in a continuum of intensity in a decentralized supply chain. Also, we find that trust evolves and for some echelons it grows over time. We further examine trust in customer and trust in supplier along the supply chain. Our results suggest that trust in supplier is the lowest in the middle of supply chain and that trust in customer decreases while moving upstream along a decentralized supply chain. Finally, we study the impact of trust in inventory replenishment decision and analyze data at individual and echelon level. Our results show that low trust in customer is linked to high order quantity and long order time intervals at the individual levels. Also, results on the echelon level suggest that distributor exhibits the lowest trust, highest order quantity and largest order time intervals among echelons, and retailer is the only echelon that considers trust in supplier while placing order quantities to upstream supplier. We further explore the inventory holding behavior of managers and find that inventory managers hold higher inventory level when they have lower trust in customer and trust in their upstream supplier. This research fits within the behavioral operations field

Architecture Supporting Computational Trust Formation

Trust is a concept that has been used in computing to support better decision making. For example, trust can be used in access control. Trust can also be used to support service selection. Although certain elements of trust such as reputation has gained widespread acceptance, a general model of trust has so far not seen widespread usage. This is due to the challenges of implementing a general trust model. In this thesis, a middleware based approach is proposed to address the implementation challenges. The thesis proposes a general trust model known as computational trust. Computational trust is based on research in social psychology. An individual’s computational trust is formed with the support of the proposed computational trust architecture. The architecture consists of a middleware and middleware clients. The middleware can be viewed as a representation of the individual that shares its knowledge with all the middleware clients. Each application uses its own middleware client to form computational trust for its decision making needs. Computational trust formation can be adapted to changing circumstances. The thesis also proposed algorithms for computational trust formation. Experiments, evaluations and scenarios are also presented to demonstrate the feasibility of the middleware based approach to computational trust formation