In this paper, we describe a group key management protocol for hierarchical sensor networks where instead of using pre-deployed keys, each sensor node generates a partial key dynamically using a function. The function takes partial keys of its children as arguments. The design of the protocol is motivated by the fact that traditional cryptographic techniques are impractical in sensor networks because of associated high energy and computational overheads. The group key management protocol supports the establishment of two types of group keys; one for the nodes within a group (intra-cluster), and the other among a group of cluster head (inter-cluster). The protocol handles freshness of the group key dynamically, and eliminates the involvement of a trusted third party (TTP). We have experimentally analyzed the time and energy consumption in broadcasting partial keys and the group key under two sensor routing protocols (Tiny-AODV and Tiny-Diffusion) by varying the number of nodes and key sizes. The performance study provides the optimum number of partial keys needed for computing the group key to balance the key size for security requirements and the power consumption. The experimental study also concludes that the energy consumption of SPIN [9] increases rapidly as the number of group members increases in comparison to our protocol. Similarly the pre-deployed key approach requires more communication time in comparison with this protocol. We have implemented this protocol using MICA2 motes and repeated most of the experiments which are done in simulation and we found out that the obtained results are very close to the observations made using the simulator.

In this paper, some existing perceptual encryption algorithms of MPEG videos are reviewed and some problems, especially security defects of two recently proposed MPEG-video perceptual encryption schemes, are pointed out. Then, a simpler and more effective design is suggested, which selectively encrypts fixed-length codewords (FLC) in MPEG-video bitstreams under the control of three perceptibility factors. The proposed design is actually an encryption configuration that can work with any stream cipher or block cipher. Compared with the previously-proposed schemes, the new design provides more useful features, such as strict size-preservation, on-the-fly encryption and multiple perceptibility, which make it possible to support more applications with different requirements. In addition, four different measures are suggested to provide better security against known/chosen-plaintext attacks.

Existing wireless networks usually provide multiple data transmission rates. This paper presents a simulation study on the performance of multiple-rate mobile ad hoc networks (MANETs), based on an evolved ns-2 simulator. At the physical layer, realistic models such as Walfisch-Ikagami radio propagation model and lognormal fading are implemented. At the link layer, a link adaptation algorithm is implemented to select an appropriate data transmission rate based on the receiving signal-to-noise ratio.  At transport and application layers, different data traffics, including constant bit rate, TCP, voice over IP, and video, are generated.  We study the network performance such as throughput, delivery ratio, and end-to-end delay when position-based routing is used. We also study how node mobility and position error affect the performance. In addition, we investigate the impact of the link distance, namely the geographic distance for a hop, on the end-to-end network throughput.  This work is a comprehensive simulation study on the impact of various factors on the performance of MANETs. It also provides guidelines for future protocol and algorithm design.

This paper studies efficient and simple data broadcast in IEEE 802.15.4-based ad hoc networks (e.g., ZigBee). Since finding the minimum number of rebroadcast nodes in general ad hoc networks is NP-hard, current broadcast protocols either employ heuristic algorithms or assume extra knowledge such as position or two-hop neighbor table. However, the ZigBee network is characterized as low data rate and low cost. It cannot provide position or two-hop neighbor information, but it still requires an efficient broadcast algorithm that can reduce the number of rebroadcast nodes with limited computation complexity and storage space. To this end, this paper proposes self-pruning and forward node selection algorithms that exploit the hierarchical address space in ZigBee networks. Only one-hop neighbor information is needed; a partial list of two-hop neighbors is derived without exchanging messages between neighboring nodes. The ZigBee forward node selection algorithm finds the minimum rebroadcast nodes set with polynomial computation time and memory space. Using the proposed localized algorithms, it is proven that the entire network is covered.  Simulations are conducted to evaluate the performance improvement in terms of the number of rebroadcast nodes, number of duplicated receivings, coverage time, and communication overhead.

In ad hoc networks, malicious nodes can carry wormhole attacks to fabricate a false scenario on neighbor relations among mobile nodes. The attacks threaten the safety of ad hoc routing protocols and some security enhancements. We propose a classification of the attacks according to the format of the wormholes. It establishes a basis on which the detection capability of the approaches can be identified. The analysis shows that previous approaches focus on the prevention of wormholes between neighbors that trust each other. As a more generic approach, we present an end-to-end mechanism that can detect wormholes on a multi-hop route. Only trust between the source and the destination is assumed. The mechanism uses geographic information to detect anomalies in neighbor relations and node movements. To reduce the computation and storage overhead, we present a scheme, Cell-based Open Tunnel Avoidance(COTA), to manage the information. COTA achieves a constant space for every node on the path and the computation overhead increases linearly to the number of detection packets. We prove that the savings do not deteriorate the detection capability. The schemes to control communication overhead are studied.  We show by simulations and experiments on real devices that the proposed mechanism can be combined with existent routing protocols to defend against wormhole attacks.

Active network is an excellent paradigm to provide customized network services to the applications by allowing them to inject specific program to the intermediate routers. Active networks provide the flexibility for the application programs to modify the services that a router can provide to suit its specific needs. Therefore, it has the potential to provide application-level quality of service (QoS) at the transport and network layers. In this paper, we present an adaptable network architecture, called ADNET, which provides mechanisms to allow the application adapt to the resource constraints to achieve improved QoS. Our design aims to unify different QoS control mechanisms (e.g. integrated services, differentiated services, and active networks) together to provide a wide range of network services to all users to meet their specific needs. We propose a new fragmentation scheme with low overhead (!5%) to transfer large-size multimedia data. Using this fragmentation scheme, a new transport protocol, called ACtive Transport Protocol (ACTP) is integrated with the design. We use a new measure, called usefulness, to better reflect the QoS perceived by the end-users. In our experiments, we compare different schemes of video transmissions: non-active transport protocols such as UDP and TCP with IP fragmentation, ACTP framework with active networks,  and ACTP framework without active networks. The ACTP scheme with active networks outperforms the others in achieving application level QoS.

Privacy is needed in ad hoc networks. An ad hoc on-demand position-based private routing algorithm, called AO2P, is proposed for communication anonymity. Only the position of the destination is exposed in the network for route discovery. To discover routes with the limited routing information, a receiver contention scheme is designed for determining the next hop. Pseudo identifiers are used for data packet delivery after a route is established. Real identities (IDs) for the source nodes, the destination nodes, and the forwarding nodes in the end-to-end connections are kept private. Anonymity for a destination relies on the difficulty of matching a geographic position to a real node ID. This can be enforced by the use of secure position service systems. Node mobility enhances destination anonymity by making the match of a node ID with a position momentary. To further improve destination privacy, R-AO2P is proposed. In this protocol, the position of a reference point, instead of the position of the destination, is used for route discovery. Analytical models are developed for evaluating the delay in route discovery and the probability of route discovery failure. A simulator based on ns-2 is developed for evaluating network throughput. Analysis and simulation results show that, while AO2P preserves communication privacy in ad hoc networks, its routing performance is comparable with other position-based routing algorithms.

We present CollectCast, a peer-to-peer (P2P) service for media streaming where a receiver peer is served by multiple sender peers. CollectCast operates at the application level but infers underlying network properties to correlate end-to-end connections between peers. The salient features of CollectCast include: (1) a novel multisender selection method that exploits the performance correlation and dependency among connections between different candidate senders and the receiver, (2) a customization of network tomography techniques and demonstration of improved practicality and efficiency, and (3) an aggregation-based P2P streaming mechanism that sustains receiver-side quality in the presence of sender/network dynamics and degradation. We have performed both real-world (on PlanetLab) and simulation evaluation of CollectCast. Our simulation results show that for a receiver, CollectCast makes better selection of multiple senders than other methods that do not infer underlying network properties. Our PlanetLab experiments are performed using a P2P media streaming application (called PROMISE) which we developed on top of CollectCast. Both packet-level and frame-level performance of MPEG-4 video streaming demonstrates the practicality and effectiveness of CollectCast.

Increasing popularity of online auctions and the associated frauds have drawn the attention of many researchers. It is found that most of the auction sites prefer English auction to other auction mechanisms. The ease of adopting multiple fake identities over the Internet nourishes shill bidding by fraudulent sellers in English auction. In this paper we derive an equilibrium bidding strategy to counteract shill bidding in online English auction. We develop an algorithm based on this strategy.  An eBay like auction environment is simulated. Experiments are conducted in this environment to evaluate this strategy.  Five more popular bidding strategies are compared with the proposed strategy. In the experiment, the bidders are randomly assigned a bidding strategy. All the bidders draw their valuation from the uniform distribution. The bidders compete to buy a product in the presence of a shill. The average expected utility of the agents with proposed strategy is found to be the highest when the auction continues for a longer duration.

We propose a new architecture for on-demand media streaming centered around the peer-to-peer (P2P) paradigm. The key idea of the architecture is that peers share some of their resources with the system. As peers contribute resources to the system, the overall system capacity increases and more clients can be served. The proposed architecture employs several novel techniques to: (1) use the often-underutilized peers

Multimedia data security is important for multimedia commerce. Previous cryptography studies have focused on text data. The encryption algorithms developed to secure text data may not be suitable to multimedia applications because of large data sizes and real time constraint. For multimedia applications, light weight encryption algorithms are attractive. In this paper, we present four fast MPEG video encryption algorithms. These algorithms use a secret key randomly changing the sign bits of of DCT coefficients and/or the sign bits of motion vectors. The encryption effects are achieved by the IDCT during MPEG video decompression processing. These algorithms add very small overhead to MPEG codec. Software implementations are fast enough to meet the real time requirement of MPEG video applications. Our experimental results show that these algorithms can achieve satisfactory results. We believe that they can be used to secure video-on-demand, video conferencing and video email applications.

A mobile ad hoc network is a collection of wireless terminals that can be deployed rapidly. Its deficiencies include limited wireless bandwidth efficiency, low throughput, large delays, and weak security. Integrating it with a wellestablished cellular network can improve communication and security in ad hoc networks, as well as enrich the cellular services. This research proposes a cellular-aided mobile ad hoc network (CAMA) architecture, in which a CAMA agent in the cellular network manages the control information, while the data is delivered through the mobile terminals (MTs). The routing and security information is exchanged between MTs and the agent through cellular radio channels. A position-based routing protocol, the multi-selection greedy positioning routing (MSGPR) protocol, is proposed. At times due to the complicated radio environment, the position information is not precise. Even in these cases, the MT can still find its reachable neighbors (the association) by exchanging ”hello” messages. This association is used in complement with the position information to make more accurate routing decisions. Simulation results show that the delivery ratio in the ad hoc network is greatly improved with very low cellular overhead. The security issues in the proposed architecture and the corresponding solutions are addressed. The experimental study shows that CAMA is much less vulnerable than a pure ad hoc network.

This article recommends the teaching journal as a method of instructional improvement. Drawing on teacher education literature, the article reviews the concept of reflective teaching and then describes uses of the teaching journal for college instructors in descriptive, comparative, and critical dimensions. Teaching journals can improve the teaching not only of beginners but also of experienced instructors.

The antidote to perceived risk is trust, and transactions on the Internet are rife with perceived risk. This article establishes a need for trust messages online in a broader context of declining social trust, reviews trust literature, and then provides four tenets of trust that provide a basis for such rhetorically constructed messages. In addition to offering foundations for the rhetorical construction of trust online, the article presents 2 rhetorical paradoxes of trust that contain both opportunity and danger for scholars and netizens alike.