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In this paper, we present a signcryption scheme called CP ABSC based on Ciphertext-Policy Attribute Based Encryption (CP ABE) [7] to secure the multicast communications in smart grids that require access control, data encryption, and authentication to ensure message integrity and confidentiality. CP ABSC provides algorithms for key management, signcryption, and designcryption. It can be used to signcrypt a message based on the access rights specified by the message itself. A user can designcrypt a ciphertext if and only if it possesses the attributes required by the access structure of the data. Thus CP ABSC effectively defines a multicast group based on the access rights of the data specified by the data itself, which differs significantly from the traditional Internet based multicast where the destination group is predetermined and must be known by the data source. CP ABSC provides collusion attack resistance, message authentication, forgery prevention, and confidentiality. It can be easily applied in smart grids to secure the instructions/commands broadcast from a utility company to multiple smart meters (push-based multicast) and the data retrieved from a smart meter to multiple destinations (pull-based multicast). Compared to CP ABE, CP ABSC combines encryption with signature at a lower computational cost for signcryption and a slightly higher cost in designcryption for signature verification. We also consider the adoption of attribute-based signature (ABS), and conclude that CP ABSC has a much lower computational cost than ABS. [ABSTRACT FROM AUTHOR]

In widely deployed wireless 'hot-spot' networks, nodes frequently join or leave, and inelastic/elastic and saturated/nonsaturated flows coexist. In such dynamic and diverse environments, it is challenging to maximize the channel utilization while providing satisfactory user experiences. In this paper, we propose a novel contention-on-demand (CoD) MAC scheme to address this problem. The CoD scheme consists of a fixed-CW algorithm, a dynamic-CW algorithm, and an admission control rule. The fixed-CW algorithm allows elastic flows to access limited system bandwidth; the dynamic-CW algorithm enables inelastic flows to contend for channel on demand and quickly adapt to network change; and the admission control rule rejects overloaded traffic for providing good user experiences. We then perform an asymptotic analysis to develop a simple and practical admission control rule for homogeneous and heterogeneous traffic; our rule can not only adapt to the change in offered loads and node number, but also maximize the system utilization . Finally, extensive simulations verify that our scheme is very effective and our theoretical result is very accurate. [ABSTRACT FROM AUTHOR]

Cognitive radio networks (CRNs) are drawing more and more attention along with the increasingly scarce spectrum resource. A CRN can be easily invalid due to stochastic activities of primary users. How to sustain the connectivity of CRNs and prolong the lifetime of CRNs become challenging issues. Inspired by the success of constructing a connected dominating set (CDS) as a virtual backbone in traditional wireless networks to prolong the lifetime of the network, we study the CDS construction in CRNs in this paper. We propose a three-phase centralized algorithm and a distributed algorithm. Theoretical analysis shows that our algorithms have better performance than that of existing results. [ABSTRACT FROM AUTHOR]

In mobile ad-hoc cognitive radio networks (CRNs), end-to-end paths with available spectrum bands for secondary users may exist temporarily, or may never exist, due to the dynamism of the primary user activities. Traditional CRN routing algorithms, which typically ignore the intermittent connectivity of network topology, and traditional mobility-assisted routing algorithms, which generally overlook the spectrum availability, are obviously unsuitable. To tackle this challenge, we propose a Mobility-Assisted Routing algorithm with Spectrum Awareness (MARSA) to select relays based on not only the probability that a node meets the destination but also the chance at which there exists at least one available channel when they meet. To the best of our knowledge, this paper is the first to bring the idea of mobility-assisted routing to deal with the intermittently connected attribute of mobile ad-hoc CRNs, and the first to enhance the mobility-assisted routing by considering the temporal , spatial, and spectrum domains at the same time. Our simulation results demonstrate the superiority of MARSA over traditional algorithms in intermittently connected mobile CRNs. [ABSTRACT FROM AUTHOR]

Mobile social networking becomes increasingly popular with the explosive growth of mobile devices. By allowing mobile users to interact with potential friends around the real world, it enables new social interactions as a complement to Web-based online social networks. In this paper, we introduce a secure friend discovery mechanism based on encounter history in mobile social networks. By exploring the fact that sharing encounters indicate common activities and interests, our scheme can help people make friends with like-minded strangers nearby. To the best of our knowledge, this is the first work to take advantage of the encounter history in friend discovery. We provide peer-to-peer confidential communications with the location privacy and encounter privacy being strictly preserved. Unlike most existing works that either rely on a trusted centralized server or existing social relationships, our algorithm is designed in an ad hoc model with no such limitation. As a result, our design is more suitable and more general for mobile social scenarios. Extensive theoretical analysis and experimental study are conducted, and the results indicate that our scheme is feasible and effective for privacy-preserving friend discovery in mobile social networks. [ABSTRACT FROM AUTHOR]

This paper focuses on designing a distributed medium access control algorithm for fairly sharing network resources among contending stations in an 802.11 wireless network. Because the notion of fairness is not universal and there lacks a rigorous analysis on the relationships among the four types of most popular fairness criteria, we first mathematically prove that there exist certain connections between these types of fairness criteria. We then propose an efficient medium access algorithm that aims at achieving time fairness and throughput enhancement in a fully distributed manner. The core idea of our proposed algorithm lies in that each station needs to select an appropriate contention window size so as to fairly share the channel occupancy time and maximize the throughput under the time fairness constraint. The derivation of the proper contention window size is addressed rigorously. We evaluate the performance of our proposed algorithm through an extensive simulation study, and the evaluation results demonstrate that our proposed algorithm leads to nearly perfect time fairness, high throughput, and low collision overhead. [ABSTRACT FROM AUTHOR]