Broadcast authentication mechanisms are essential to cyber-physical systems that communicate through wireless links such as wireless sensor networks (WSN) and body area network (BAN). Even though symmetric key-based authentication schemes are more prevalent among these systems, public key-based digital signature schemes have started to gain ground; notably, several research efforts have been focused on the Elliptic Curve Cryptosystem due to its low overheads. As a combination of sensing and computing platform, WSN must handle both time-sensitive as well as delay-tolerant but security-sensitive data. The cryptographic strength and verification delay of an elliptic curve digital signature are determined by the parameters of the curve's underlying finite held. The held's parameters and public key are usually generated and distributed before the WSN's deployment thus cannot be changed easily. This situation creates a need for a multi-resolution digital signature scheme that provides the signer a choice to trade off a signature's strength for faster verification time and less power consumption. In this paper, we present a digital signature scheme called Multi-Resolution Elliptic Curve Signature (MRECS) that allows the signer the ability to create signatures of different strengths from the same public key set. Compared to an implementation using a set of different keys, MRECS requires less storage overhead and has longer key lifetime at the cost of slightly higher but acceptable communication overhead. MRECS yields up to 33% computational overhead reduction compared to that of the full-size signature while maintaining a full elliptic curve strength regardless of a signature strength.

Due to simpler protocol operations, e.g. no synchronization and higher tolerance to node capture attack compared to symmetric key-based approaches, public key-based (PKC) approaches have gained popularity in wireless sensor network (WSN) broadcast authentication. With PKC's security strength, a sens

Steganography is the art of secret communication between two parties that not only conceals the contents of a message but also its existence. Steganalysis attempts to detect the existence of embedded data in a steganographically altered cover file. Many algorithms have been proposed, but so far each has some weakness that has allowed its effects to be detected, usually through statistical analysis of the image. In this paper, we propose a different approach to JPEG steganography that provides high embedding capacity with zero-deviant histogram restoration. Our algorithm, named J3, uses stop points in its header structure that allows it to restore the histogram completely, making its detection impossible by any first order steganalysis. It gives better results with higher order steganalysis when compared to F5, Outguess and Steghide. As far as we know, there is no existing algorithm that can provide as high an embedding payload with complete histogram restoration.

This paper describes the architecture and implementation of a Java-based appliance for collaborative review of crashes involving injured children in order to determine mechanisms of injury. The multidisciplinary expertise needed for such reviews is not available at any one institution, resulting in

A theoretical channel to communicate covertly through mix-firewalls has been discussed in previous work. This paper describes implementing this theoretical construction in an actual system. Practical issues involved in implementation are analyzed, and an actual design is given here. Suggested parameters for concatenated codes for the experimental channel are also provided, based on experimental results. We compare our numerically computed information theoretic results for the data rate of covert channels through timed mix-firewalls to the data rate obtained by our actual construction of these covert channels.

To achieve high performance and resilience to failures, many peer-to-peer (P2P) systems have begun to use striping and collaborative downloading, where each peer can download the file or pieces of the file from a number of peers in parallel, and at the same time, serve them to some other peers. These P2P systems intrinsically involve many-to-many mappings from the servers to the clients (or peers to peers) as well as many-to-one mappings from the clients to the server. In this paper, we present a node selection algorithm that generates an optimal server set with respect to the worst link stress (WLS) criterion for a single client and evaluates its network performance metrics for many- to-many mappings and many-to-one mappings. Simulation results show that our system is simple yet effective in achieving the design goals. In particular, it minimizes the level of congestion at the bottleneck link, and it consumes less network resources in terms of total bandwidth usage. The objectives of this in-depth examination are to raise awareness and concern for these issues and to provide alternatives or improved designs that can be incorporated into many P2P systems.

Impulse noise sources such as dimmers, halogen lamps etc., are quite common in power line networks. Hence, high-speed power line communications systems should be designed to deal effectively with them. HomePlug AV uses aggressive channel adaptation at the physical layer and efficient retransmissions at the MAC layer to deal with impulse noise. This approach can lead to very high probability (up to 20%) of Forward Error Correction (FEC) block errors under some channel conditions. HomePlug AV also has large transmission overhead to ensure reliable communication over the powerline. Transmission overhead can negatively impact the MAC efficiency on channels with high FEC Block Error Rate (BLER) due the need for a large number of retransmissions to successfully deliver packets. This paper studies the complex interaction between FEC block errors, transmission overhead, Quality of Service (QoS) requirements of a multimedia stream and its TDMA allocation requirements. Our results show that, to support low latency applications at high BLERs, the average allocation size has to be increased by one or more transmission overheads. Further, the increase in average allocation is not a strong function of application data rate. Hence, low data rate applications can suffer significant loss in efficiency at high BLERs. Our results also show that using a fixed size TDMA allocation can lead to poor utilization when the latency requirements of the application are less than four beacon periods. These results indicate that channel adaptation in HPAV should take into consideration the application QoS requirements to optimize the overall system capacity.

In this paper we describe the protection goals and mechanisms in HomePlug AV, a next-generation power-line communications standard. This is a fascinating case-history in security usability. There are also novel protocol issues; interactions with mechanisms at other layers; and opportunities for both researchers and third-party vendors to build on the mechanisms provided. The central problem -- being sure whether a device being enrolled in the network is the device you think, not a similar one nearby -- is not well solved by conventional mechanisms such as public-key infrastructures, but appears to require either very old-fashioned or very novel approaches.

There is industrial intent to use powerline communication (PLC) networks in the home for delivery of multimedia data, with associated challenging quality of service (QoS) requirements. Existing protocols for PLC, for wireless networks, or even for wired networks cannot meet these challenges efficiently. This paper proposes and analyzes a new protocol designed to provide the high QoS needed for delivery of multiple multimedia streams in a PLC environment. The proposed protocol, periodic contention-free multiple access (PCF/MA), directly addresses the issues of channel noise, hidden nodes and near-far effects. The proposed PCF/MA performance is analyzed theoretically and its performance is simulated. The results show that 85Mbps MAC throughput is possible with 100Mbps channel data rate, even when there are hidden nodes in the network.

The HomePlug 1.0 standard allows high-speed communication on low-voltage power lines without a requirement for new wires. Effective use of the power line bandwidth requires a robust medium access control (MAC) protocol to mitigate the harsh conditions of the power line channel as well as the capability to support prioritized multimedia traffic. This paper briefly describes the HomePlug 1.0 MAC and PHY protocols, which allow prioritized channel access. It then presents field test results comparing this with the more familiar IEEE 802.11b protocol.

At present, "capacity" is the prevailing paradigm for covert channels. With respect to steganography, however, capacity is at best insufficient, and at worst, is incorrect. In this paper, we propose a new paradigm called "capability" which gauges the effectiveness of a steganographic method. It includes payload carrying ability, detectability, and robustness components. We also discuss the use of zero-error capacity for channel analysis and demonstrate that a JPEG compressed image always has the potential to carry hidden information.

Effective use of limited network resources is crucial in supporting network-based multimedia applications. A K-metric altruistic Qos routing algorithm is proposed to tackle the issue of network resource overcommitmnent. based on this algorithm, a multimedia dispersion scheme is developed to alleviate the high blocking ratio problem caused by high bandwidth requirement. Our evaluation shows that the proposed scheme is capable of achieving at 30% improvement in terms of reducing the average blocking ratio.

Wireless LANs are becoming increasingly available, affordable and attractive due to their increasing speeds and decreasing costs, in addition to their ability to offer easy configuration and reconfiguration of nodes in a LAN. However, most commercial wireless LAN products have limited security over the link, and none that we are aware of use NSA-approved cryptographic methods. This paper describes a system developed jointly by a team at the University of Florida in its Integrated Process and Product Design (IPPD) course and a liaison engineer at Raytheon Systems Division that uses Fortezza cryptographic cards to provide authenticated, encrypted connections between hosts running MS Windows.

Classical covert channel analysis has focused on channels available on a single computer: timing channels and storage channels. We characterize network covert channels. Potential network covert channels are exploited by modulating transmission characteristics. We distinguish between spatial covert channels, caused by a variation in the relative volume of communication between nodes in the network, and temporal covert channels caused by a variation in transmission characteristics over time, extending the work of Girling (1987). A model for obtaining a spatially neutral transmission schedule was given by Newman-Wolfe and Venkatraman (1991, 1992). Temporally neutral transmissions are characterized and scheduling policies to generate temporally neutral transmission schedules were given by Venkatraman and Newman-Wolfe (1993). We estimate the covert channel capacity using an adaptive scheduling policy, modeling the system as a mode secure system. Based on our measurements on the University of Florida campus-wide backbone network (UFNET), we discuss the auditability of network covert channels and suggest some handling policies to reduce the capacity of these covert channels to TCSEC acceptable levels.>

We provide cost estimates for achieving spatial neutrality under realistic network traffic conditions using two methods. Measurements done on the University of Florida campus wide backbone network (UFNET) provide us with considerable experience to model an actual network better. Simulation results show that the algorithm's improvement over padding alone is greater for a sparse traffic matrix than for a uniform random traffic matrix. It accomplishes this by smoothing the traffic matrix by rerouting, reducing the padding overhead required to achieve a neutral traffic matrix. On the other hand, a sparse traffic matrix leads to increased costs over uniform random traffic matrix for both padding alone and for padding with rerouting. Experiments done with UFNET traffic characteristics show that the costs are such that the proposed method can be employed in actual networks, under moderate load conditions, to achieve traffic neutrality with acceptable overheads.>

We propose scheduling strategies to determine transmission schedules that prevent traffic analysis and the creation of covert channels due to temporal variation in the transmission of packets. In addition to requiring the traffic matrix be neutral we require the transmission schedule be temporally neutral to eliminate that potential coved channel. The static scheduling policy generates temporally neutral transmission schedules. We extend this to develop an adaptive scheduling policy that can adapt to long term load fluctuations. The adaptive algorithm is expensive and there exists the possibility of a low bandwidth and noisy covert channel; we suggest mechanisms to reduce the bandwidth of the covert channel. The tradeoff is between the "adaptability" of the scheduling policy and the bandwidth of the covert channel.>

One of the stated goals of communications security is the prevention of traffic analysis. A model to prevent traffic analysis by rerouting and padding the traffic matrix, so that the apparent final traffic matrix is neutral, is analyzed. The objective of this analysis is to justify the claims of the model and to show that rerouting of traffic via intermediate nodes with minimum padding is indeed a cost effective method to prevent traffic analysis. Simulation results supporting the above claim are also presented. The requirement that final traffic matrix be neutral may be too restrictive in some cases, and various modifications to the model are suggested, while still ensuring prevention of traffic analysis. Prevention of traffic analysis in real time is addressed briefly. >

Ensemble is an X-Windows based, object-oriented graphics editor based on the tgif graphics editor from UCLA.It relies on Unix* 4.3bsd sockets and can be used as a stand-alone program or as an application in the University of Florida's distributed conferencing system (DCS).It uses implicitly placed write locks for concurrency control, with locks placed when an object is selected and removed when it is deselected.Multiple users may read or edit a file concurrently, with all users receiving updates whenever a lock is removed.Pointers are shared by mutual consent, so that users may collaborate to the degree desired.Ensemble is a prototype lock-based approach to object-oriented concurrent graphics editing.

A distributed mutual exclusion algorithm based on Huffmann trees is described. A request message is passed from a leaf node all the way to the root, signaling that a node is allowed to enter the critical section. Fault tolerance is achieved by forming the Huffman tree dynamically. It is shown that the approach has broad applications in distributed systems where nodes are often organized as a logical tree for ease of coordination. High fault tolerance is achieved, since a faulty node can be detected by its neighbor and thus be deleted from the tree.>

The paper gives a mathematical model for prevention of traffic analysis in network security and suggests an approach for prevention of unauthorized release of information concerning traffic patterns. The model assumes that an eavesdropper may read the contents of all links, including the source and destination, and that all countermeasures are performed at the transport layer. The goal of the countermeasures is to prevent the eavesdropper from gaining any useful information regarding the traffic patterns in a cost efficient and feasible manner. Countermeasures performed at the transport level include encryption a limited form of message rerouting delaying messages and sending dummy messages as needed within resource capacities. By formulating the problem in terms of systems of equalities and systems of inequalities linear programming methods may be used to find solutions to the traffic analysis security problem.>

An efficient dynamic graph traversal algorithm is used to identify nonconflicting requests and to allocate network resources in a dynamically partitionable bus network (DPBN). In centralized network control a special processor receives from the control computer of a partitionable bus network an adjacency matrix which indicates conflicts among requests. It applies the dynamic graph traversal algorithm and returns the identified nonconflicting requests to the control computer. The control computer then physically partitions the network into a number of subnetworks for processing the nonconflicting requests in parallel. In distributed control, each station determines conflicts and sets the switches. The results of performance evaluation show a 40% decrease of network delay as compared with a fully utilized, but unpartitioned local area network.>

A wait-free solution to the atomic (r,1kCRWW problem is presented.It uses (r+2)(Sr+2+6)-I safe, multi-reader bits to implement a &bit variable shared among t readers and 1 writer, solving an open question of Lamport [Lamport '851.Thus, it closes a gap in the simulation of systems of shared variables for single writers.It differs from other approaches to this problem in that mutual exclusion is maintained between the writer and other processes on the copies of the shared variable used in the implementation.