Visible Light Communication (VLC) technology using light emitting diodes (LEDs) has been gaining increasing attention in recent years as it is appealing for a wide range of applications such as indoor positioning. Orthogonal frequency division multiplexing (OFDM) has been applied to indoor wireless optical communications in order to mitigate the effect of multipath distortion of the optical channel as well as increasing data rate. In this paper, we investigate the indoor positioning accuracy of optical based OFDM techniques used in VLC systems. A positioning algorithm based on power attenuation is used to estimate the receiver coordinates. We further calculate the positioning errors in all the locations of a room and compare them with those using single carrier modulation scheme, i.e., on-off keying (OOK) modulation. We demonstrate that OFDM positioning system outperforms its conventional counterpart.

Many key predistribution (KP) protocols have been proposed and are well accepted in randomly deployed wireless sensor networks (WSNs). Being distributed and localized, they are perceived to be scalable as node density and network dimension increase. While it is true in terms of communication/computation overhead, their scalability in terms of security performance is unclear. In this paper, we conduct a detailed study on this issue. In particular, we define a new metric called Resilient Connectivity (RC) to quantify security performance in WSNs. We then conduct a detailed analytical investigation on how KP protocols scale with respect to node density and network dimension in terms of RC in randomly deployed WSNs. Based on our theoretical analysis, we state two scaling laws of KP protocols. Our first scaling law states that KP protocols are not scalable in terms of RC with respect to node density. Our second scaling law states that KP protocols are not scalable in terms of RC with respect to network dimension. In order to deal with the unscalability of the above two scaling laws, we further propose logical and physical group deployment, respectively. We validate our findings further using extensive theoretical analysis and simulations.

In many Wireless Sensor Networks (WSNs), providing end to end secure communications between sensors and the sink is important for secure network management. While there have been many works devoted to hop by hop secure communications, the issue of end to end secure communications is largely ignored. In this paper, we design an end to end secure communication protocol in randomly deployed WSNs. Specifically, our protocol is based on a methodology called differentiated key pre-distribution. The core idea is to distribute different number of keys to different sensors to enhance the resilience of certain links. This feature is leveraged during routing, where nodes route through those links with higher resilience. Using rigorous theoretical analysis, we derive an expression for the quality of end to end secure communications, and use it to determine optimum protocol parameters. Extensive performance evaluation illustrates that our solutions can provide highly secure communications between sensor nodes and the sink in randomly deployed WSNs. We also provide detailed discussion on a potential attack (i.e. biased node capturing attack) to our solutions, and propose several countermeasures to this attack.

Null data frames are a special but important type of frames in IEEE 802.11 WLANs. They are widely used in 802.11 WLANs for control purposes such as power management, channel scanning, and association keeping alive. The wide applications of null data frames come from their salient features such as lightweight frame format and implementation flexibility. However, such features can be taken advantage of by malicious attackers to launch a variety of attacks on 802.11 WLANs. In this paper, we identify potential security vulnerabilities in current null data frame applications in 802.11 WLANs. We then study two types of attacks taking advantage of these vulnerabilities in detail that are functionality-based Denial-of-Service attack and implementation-based fingerprinting attack. We also evaluate their effectiveness based on extensive experiments. Furthermore, we design and implement novel defense mechanisms against the attacks, and evaluate their effectiveness based on extensive experiments. Although our proposed defenses help alleviate the vulnerabilities, completely eliminating the vulnerabilities brought by null data frames remains an open issue. Finally, we point out that our work has broader impact in that similar vulnerabilities exist in many other networks due to the adoption of simple and lightweight messages for control purpose.

Securely authenticating a human user without assistance from any auxiliary device in the presence of powerful passive adversaries is an important and challenging problem. Passive adversaries are those that can passively monitor, intercept, and analyze every part of the authentication procedure, except for an initial secret shared between the user and the server. In this paper, we propose a new secure authentication scheme called predicate-based authentication service (PAS). In this scheme, for the first time, the concept of a predicate is introduced for authentication. We conduct analysis on the proposed scheme and implement its prototype system. Our analytical data and experimental data illustrate that the PAS scheme can simultaneously achieve a desired level of security and user friendliness.

Null data frames are a special but important type of frames in IEEE 802.11 based wireless local area networks (e.g., 802.11 WLANs). They are widely used for power management, channel scanning and association keeping alive. The wide applications of null data frames come from their salient features such as lightweight frame format and implementation flexibility. However, such features can be taken advantage of by malicious attackers to launch a variety of attacks. In this paper, we identify the potential security vulnerabilities in the current applications of null data frames. We then study two types of attacks taking advantage of these vulnerabilities in detail, and evaluate their effectiveness based on extensive experiments. Finally, we point out that our work has broader impact in that similar vulnerabilities exist in many other networks.

In this paper, we study the issue of sensor network deployment using limited mobility sensors. By limited mobility, we mean that the maximum distance that sensors are capable of moving to is limited. Given an initial deployment of limited mobility sensors in a field clustered into multiple regions, our deployment problem is to determine a movement plan for the sensors to minimize the variance in number of sensors among the regions and simultaneously minimize the sensor movements. Our methodology to solve this problem is to transfer the nonlinear variance/movement minimization problem into a linear optimization problem through appropriate weight assignments to regions. In this methodology, the regions are assigned weights corresponding to the number of sensors needed. During sensor movements across regions, larger weight regions are given higher priority compared to smaller weight regions, while simultaneously ensuring a minimum number of sensor movements. Following the above methodology, we propose a set of algorithms to our deployment problem. Our first algorithm is the optimal maximum flow-based (OMF) centralized algorithm. Here, the optimal movement plan for sensors is obtained based on determining the minimum cost maximum weighted flow to the regions in the network. We then propose the simple peak-pit-based distributed (SPP) algorithm that uses local requests and responses for sensor movements. Using extensive simulations, we demonstrate the effectiveness of our algorithms from the perspective of variance minimization, number of sensor movements, and messaging overhead under different initial deployment scenarios.

Abstract—Many wireless sensor network (WSN) applications demand secure communications. The random key predistribution ðRKPÞ protocol has been well accepted in achieving secure communications in WSNs. A host of key management protocols have been proposed based on the RKP protocol. However, due to the randomness in key distribution and strong constraint in key path construction, the RKP-based protocols can only be applied in highly dense networks, which are not always feasible in practice. In this paper, we propose a methodology called network decoupling to address this problem. With this methodology, a WSN is decoupled into a logical keysharing network and a physical neighborhood network, which significantly releases the constraint in key path construction of the RKP protocol. We design two new key management protocols, that is, RKP-DE and RKP-DEA, as well as a set of link and path dependency elimination rules in decoupled sensor networks. Our analytical and simulation data demonstrate the performance enhancement of our solutions from the perspective of connectivity and resilience and its applicability in nonhighly dense sensor networks. Index Terms—Wireless sensor networks, random key predistribution, network decoupling. 1

Multicast services are demanded by a variety of applications. Many applications require anonymity during their communication. However, there has been very little work on anonymous multicasting and such services are not available yet. Since there are fundamental differences between multicast and unicast, the solutions proposed for anonymity in unicast communications cannot be directly applied to multicast applications. In this paper, we define the anonymous multicast system, and propose a mutual anonymous multicast (MAM) protocol including the design of a unicast mutual anonymity protocol and construction and optimization of an anonymous multicast tree. MAM is self organizing and completely distributed. We define the attack model in an anonymous multicast system and analyze the anonymity degree. We also evaluate the performance of MAM by simulations.

Secure communications are highly demanded by many wireless sensor network (WSN) applications. The random key pre-distribution (RKP) scheme has become well accepted in achieving secure communications in WSNs. However, due to its randomness in key distribution and strong constraint in key path construction, the RKP scheme can only be applied in highly dense networks, which are not always feasible in practice. In this paper, we propose a methodology called network decoupling to solve this problem. With this methodology, a wireless sensor network is decoupled into a logical key-sharing network and a physical neighborhood network, which significantly releases the constraint in key path construction of the RKP scheme. We design a secure neighbor establishment protocol (called RKP-DE) as well as a set of link and path dependency elimination rules in decoupled wireless sensor networks. Our analytical and simulation data demonstrate the performance enhancement of our solution and its applicability in non-highly dense wireless sensor networks

Sensor nodes being small in size and distributively deployed, are vulnerable to physical attacks that attempt to physically destroy sensors in the sensor network. Generally speaking, physical attacks in sensor networks can be classified into two types: blind physical attacks and search-based physical attacks. In blind attacks, sensors are destroyed using brute-force approaches (like bombs/grenades etc.). The advantage here is the rapidness in destroying sensors. The downside however, is the fact that the deployment field also suffers significant casualties. If the attacker wishes to preserve the deployment field, the attacker will conduct search-based attacks by searching for sensors in the field and destroying only the sensors. While this preserves the deployment field, the attack process is slow. In this paper, we present policy-driven physical attacks, where the bias between the twin objectives of the attacker (rapidly destroying sensors, and preserving the deployment field) is modeled as a policy for the attacker. In policy-driven physical attacks, the attacker walks through the sensor network deployment field using signal detecting equipment to locate active sensors. Depending on the attacker's policy, the attacker takes different actions during the attack process. Based on detailed performance measurement, we observe that the policy has impacts on the network performance and destruction in the deployment field, demonstrating that the attacker can achieve desired bias in its objectives under policy-driven physical attacks

Abstract—In this paper, we address a Resource Constrained Lifetime Problem in sensor networks in an operating environment subject to physical node destructions. Specifically, given a limited number of sensors, our goal is to maximize the network lifetime and derive the deployment plan of the nodes to maximize the lifetime under physical node destructions. The problem of physical destructions due to hostile environmnets and small size of the sensors is a potent threat and severely constrains the practical lifetime of sensor networks. The lifetime problem we define is representative, practical and encompasses other versions of similar problems. We also define a representative physical attack model under which we study and solve the lifetime problem. Our solutions take into account both the energy minimization and node constraints. We make several observations in this realm of which an important one is the high sensitivity of lifetime to physical attacks highlighting the importance of our study. Our work has broad and immediate impacts to system designers during network deployments in hostile environments.

The small form factor of the sensors, coupled with the unattended and distributed nature of their deployment expose sensors to physical attacks that physically destroy sensors in the network. In this paper, we study the modeling and analysis of search-based physical attacks in sensor networks. We define a search-based physical attack model, where the attacker walks through the sensor network using signal detecting equipment to locate active sensors, and then destroys them. We consider both flat and hierarchical sensor networks. The attacker in our model uses a weighted random selection based approach to discriminate multiple target choices (normal sensors and cluster-heads) to enhance sensor network performance degradation. Our performance metric in this paper is accumulative coverage (AC), which effectively captures coverage and lifetime of the sensor network. We then conduct detailed evaluations on the impacts of search-based physic attacks on sensor network performance. Our performance data clearly show that search-based physical attacks significantly reduce sensor network performance. We observe that attack related parameters, namely attacker movement speed, detection range and accuracy have significant impacts on the attack effectiveness. We also observe that the attack effectiveness is significantly impacted by sensor network parameters, namely the frequency of communication and frequency of cluster-head rotation. We believe that our work in this paper on modeling and analyzing search-based physical attacks is an important first step in understanding their overall impacts, and effectively defending against them in the future.

In this paper we study the defense of sensor networks against search-based physical attacks. We define search-based physical attacks as those, where an attacker detects sensors using signal detecting equipment and then physically destroys the detected sensors. In this paper, we propose a sacrificial node-assisted approach to defend against search-based physical attacks. The core principle of our defense is to trade short term local coverage for long term global coverage through the sacrificial node-assisted attack notification and states switching of sensors. The performance metric we use is accumulative coverage (AC), which effectively captures coverage and lifetime of the sensor networks to measure sensor network performance. Our simulation results clearly demonstrate that our defense approach can significantly decrease losses in AC even under intense search-based physical attacks.