With the parallel growth of the Android operating system and mobile malware, one of the ways to stay protected from mobile malware is by observing the permissions requested. However, without careful consideration of these permissions, users run the risk of an installed app being malware, without any warning that might characterize its nature. We propose a permission-based risk signal using a taxonomy of sensitive permissions. Firstly, we analyse the risk of an app based on the permissions it requests, using a permission sensitivity index computed from a risky permission set. Secondly, we evaluate permission mismatch by checking what an app requires against what it requests. Thirdly, we evaluate security rules based on our metrics to evaluate corresponding risks. We evaluate these factors using datasets of benign and malicious apps (43580 apps) and our result demonstrates that the proposed framework can be used to improve risk signalling of Android apps with a 95% accuracy.

IPv6 Routing Protocol for Low Power and Lossy Networks (RPL), is based on building an acyclic graph where an Objective Function (OF) is responsible for selecting the preferred parent during Destination Oriented Directed Acyclic Graph (DODAG) construction. In this paper, we propose a new multi-metric OF based on Analytical Hierarchy Processes decision masking algorithm. AHP-OF, combines a set of routing metrics aiming to provide the best routing decision for RPL to satisfy the different application requirements for LLN s such as reliable applications, real time applications and highly available applications. Here we focus on the theoretical aspect of AHP-OF, and finally we evaluate the performance of AHP-OF compared to other OFs using Cooja simulator.

Intelligent Transportation Systems (ITSs) have been instrumental in reshaping transportation towards safer roads, seamless logistics, and digital business-oriented services under the umbrella of smart city platforms. Undoubtedly, ITS applications will demand stable routing protocols that not only focus on Inter-Vehicle Communications but also on providing a fast, reliable and secure interface to the infrastructure. In this paper, we propose a novel stable infrastructure-based routing protocol for urban VANETs. It enables vehicles proactively to maintain fresh routes towards Road-Side Units (RSUs) while reactively discovering routes to nearby vehicles. It builds routes from highly stable connected intersections using a selection policy which uses a new intersection stability metric. Simulation experiments performed with accurate mobility and propagation models have confirmed the efficiency of the new protocol and its adaptability to continuously changing network status in the urban environment.

People find it difficult to remember multiple alphanumeric as well as graphical passwords. We propose a Passhint authentication system (PHAS), where the users have to choose four images and create hints for each one of them in order to register a new password. During authentication, they have to recognize only the target images, which are displayed with their corresponding hints, among collections of 15 decoy images, in a four step process. A usability study was conducted with 40 subjects. They created 1 Mikon, 1 doodle, 1 art and 1 object password and then recalled each password after a period of two weeks (without any practice sessions). The results demonstrated that the memorability of multiple passwords in PHAS is better than in existing Graphical authentication systems (GASs). Although the registration time is high, authentication time for successful attempts is either equivalent to or less than the time reported for previous GASs. A guessability study conducted with the same subjects revealed that art passwords are the least guessable, followed by Mikon, doodle and objects in that order. The results strongly suggest the use of art passwords in PHAS, which would offer usable as well as secure authentication. The preliminary results indicate that PHAS has solved the memorability problem with multiple passwords. We propose two new features that could enhance the security offered by PHAS, but the usability of these features would need to be tested before they could be adopted in practice.

Existing studies in the field of graphical authentication systems (GASs) have shown that users find it difficult to remember multiple image passwords. In this context, it is believed that memorability can be improved if target images making up a graphical password are selected using a mnemonic strategy during the registration stage. We conducted a usability study with 80 subjects, who were required to create four graphical passwords, each using a mnemonic strategy and recall them every week, for a period of four weeks. The results demonstrated that the memorability of the image passwords created using a mnemonic strategy do not improve even when compared to the existing multiple password studies. Hence remembering multiple image passwords using mnemonic strategies is a mentally demanding task. A guessability study was conducted with 70 participants to examine the vulnerability of image passwords to written descriptions. The analysis of the descriptions revealed that most passwords created in the usability study were described by the account holders using annotated/ non annotated sketch of the target images making up a password. This made all the passwords highly guessable. Based on our results we propose a hint-based authentication system, which can improve the memorability of graphical passwords and also provide adequate security. But the usability as well as security of the proposed system needs to be tested before it could be adopted in practice.

Accident Warning Systems (AWSs) use Vehicular Ad-hoc Networks to help avoid potential collisions and spread safety notifications amongst nearby vehicles. The development of such systems often assumes that the users are honest and therefore will participate as expected to maximize the intended benefit. In practice, however, attacks are a real possibility and require appropriate counter-measures to avoid a range of undesirable outcomes from reduced functionality to failure to maliciously induced traffic incidents. This paper examines the subject and identifies potential adversaries and the attacks that they might use. Finally, it proposes a threat model that presents a comprehensive picture of how security, privacy and trust issues in AWSs will be targeted and how they can be protected.

This paper presents a user study with 70 participants using four different image types: Mikon; doodle; art; object, to examine guessability of image passwords to textual descriptions The study reported in this paper will examine, whether a written (textual) copy made by an account holder for recalling the target images forming a password in subsequent use, could be used for successful authentication by an attacker. The statistical test results of the study revealed that object images had the highest guessability, followed by the doodle images. The guessability of Mikon images was either equal to or slightly higher than the art images. The results also showed that the subjects described the elements in the target image, while making a written copy of their passwords for subsequent use, in the given experimental set-up. Based on the results obtained, we recommend the use of art images as passwords in image authentication.

In this paper, we describe a novel method of approving and finalising financial transactions that would raise the bar for any potential attackers. The proposed scheme is based on the hypothesis that it would be significantly harder for an attacker to compromise two hardware devices or monitor and interfere with two communication channels at the same time. This will allow the users of this method to initiate a transaction on the Internet and then use their mobile phone in order to sanction the transfer of funds to a different account. In contrast to Two-Factor Authentication systems, this scheme does not require the online submission of any information that is received by the user's device but directly interacts through the mobile phone network. For this purpose the user's mobile phone has an additional encryption layer that allows it to communicate securely with the server side and convey the user's consent for a certain transaction. This ensures that the two channels and the authentication factors are kept independent. Therefore, even if the user's computer is compromised an attacker would not be able to set a fraudulent transaction without actually having the user's mobile phone and the unique data that are generated by the device.

Intelligent Transportation Systems have been instrumental in reshaping transportation towards safer roads, seamless logistics, and digital business-oriented services under the umbrella of smart city platforms. Broadcasting transmission is an essential operational technique that serves a broad range of applications which demand different restrictive QoS provisioning levels. Although broadcast communication has been investigated widely in highway vehicular networks, it is undoubtedly still a challenge in the urban environment due to the obstacles. In this paper, we propose the Road-Topology based Broadcast Protocol (RTBP) is proposed, a distance and contention-based forwarding scheme suitable for both urban and highway vehicular environments. RTBP aims at assigning the highest forwarding priority to a car, called a mobile repeater, having the greatest capability to send the packet in multiple directions. Realistic experimental environments are used to test the performance against well-known protocols. The results show that RTBP can reduce latency, increase reachability and save system resources.

The increasing number of collective communication-based services with a mass interest and the parallel increasing demand for service quality are paving the way toward end-to-end QoS guarantees. Although many multicast algorithms in interconnection networks have been widely reported in the literature, most of them handle the multicast communication within limited performance metrics, i.e., either delay/latency or throughput. In contrast, this study investigates the multicast communication within a group of QoS constrains, namely latency, jitter, throughput, and additional traffic caused. In this paper, we present the Qualified Groups (QGs) as a novel path-based multicast algorithm for interconnection networks. To the best of our knowledge, the QG is the first multicast algorithm that considers the multicast latency at both the network and node levels across different traffic scenarios in interconnection networks. Our analysis shows that the proposed multicast algorithm exhibits superior performance characteristics over other well-known path-based multicast algorithms under different operating conditions. In addition, our results show that the QG can significantly improve the parallelism of the multicast communication.

Conventional on-demand route discovery for ad hoc routing protocols extensively use simple flooding, which could potentially lead to high channel contention, causing redundant retransmissions and thus excessive packet collisions in the network. This phenomenon has been shown to greatly increase the network communication overhead and end to end delay. This paper proposes a new probabilistic counter-based method that can significantly reduce the number of RREQ packets transmitted during route discovery operation. Our simulation results reveal that equipping AODV routing protocol with the proposed probabilistic counter-based route discovery method can result in significant performance improvements in terms of routing overhead, MAC collisions and end-to-end delay while still achieving a good throughput.

The performance of the existing non-contiguous processor allocation strategies has been traditionally carried out by means of simulation based on a stochastic workload model to generate a stream of incoming jobs. To validate the performance of the existing algorithms, there has been a need to evaluate the algorithms' performance based on a real workload trace. In this paper, we evaluate the performance of several well-known processor allocation and job scheduling strategies based on a real workload trace and compare the results against those obtained from using a stochastic workload. Our results reveal that the conclusions reached on the relative performance merits of the allocation strategies when a real workload trace is used are in general compatible with those obtained when a stochastic workload is used.

Two strategies are used for the allocation of jobs to processors connected by mesh topologies: contiguous allocation and non-contiguous allocation. In noncontiguous allocation, a job request can be split into smaller parts that are allocated to non-adjacent free sub- meshes rather than always waiting until a single sub-mesh of the requested size and shape is available. Lifting the contiguity condition is expected to reduce processor fragmentation and increase system utilization. However, the distances traversed by messages can be long, and as a result the communication overhead, especially contention, is increased. The extra communication overhead depends on how the allocation request is partitioned and assigned to free sub-meshes. This paper presents a new noncontiguous allocation algorithm, referred to as greedy-available-busy-list (GABL for short), which can decrease the communication overhead among processors allocated to a given job. The simulation results show that the new strategy can reduce the communication overhead and substantially improve performance in terms of parameters such as job turnaround time and system utilization. Moreover, the results reveal that the shortest- service-demand-first (SSD) scheduling strategy is much better than the first-come-first-served (FCFS) scheduling strategy.

The use of adaptively-routed wormhole switched k-ary n-cubes has been motivated by the high path diversity provided by the rich topology of this family of interconnection networks. Due to its insensitivity to message destination, adaptive wormhole switching has been an attractive design alternative not only in networks suggested for contemporary multicomputers but also in the new Network-on-Chip and System-on-Chip architectures. Although analytical performance models for wormhole switched networks have been widely reported in the literature over the past two decades, the majority of these models have unrealistically assumed negligible buffering capacity at each switching element of the network. This paper proposes the first analytical model to assess the performance of adaptively-routed wormhole-switched k-ary n-cubes with finite size buffers. The new model can also accounts for the use of any number of virtual channels in order to further improve system performance. The model is validated by means of an event-driven simulator and experiments show close agreement between model predictions and simulator results.

The performance study of the existing noncontiguous processor allocation strategies has been traditionally carried out by means of simulation based on a stochastic workload model to generate a stream of incoming jobs that are submitted to and run on a given message passing parallel machine for a period of time. To validate the performance of the existing allocation algorithms, there has been need to evaluate the algorithms' performance based on a real workload trace. In this study, we evaluate the performance of several well-known processor allocation and job scheduling strategies based on a real workload trace and compare the results against those obtained from using a stochastic workload. Our results reveal that the conclusions reached on the relative performance merits of the allocation strategies when a real workload trace is used are in general compatible with those obtained when a stochastic workload is used.

Conventional on-demand route discovery methods in mobile ad hoc networks (MANET) employ blind flooding, where a mobile node blindly rebroadcasts received Route Request (RREQ) packets until a route to a particular destination is established. This can potentially lead to high channel contention, causing redundant retransmissions and thus excessive packet collisions in the network. Such a phenomenon induces what is known as broadcast storm problem, which has been shown to greatly increase the network communication overhead and end-to-end delay. In this paper, we show that the deleterious impact of such a problem can be reduced if measures are taken during the dissemination of RREQ packets. We propose two new probabilistic methods for on-demand route discovery, that is simple to implement and can significantly reduce the overhead involved in the dissemination of RREQs. Our analysis reveals that equipping AODV with probabilistic route discovery can result in significant performance improvements on all the standard metrics.

Abstract The PGPGrid project aims to parallelize the process of extracting range data from an experimental 3D scanner using the Grid as a vehicle for accessing necessary resources. The application is potentially highly parallel but has some unusual features such as rapid spawning of processes in real time and a dynamic inter‐process network topology. These characteristics are such as to require enhancement of the usual task migration capabilities of the Globus toolkit. The present paper initially discusses attempts to estimate the real parallelizability of the scanner application. It then describes a new Java application programming interface, based on Milner's $\pi$ ‐calculus, which could be used to extend Globus in a manner capable of supporting systems with this kind of dynamic parallel structure. The location of processing resources for the $\pi$ ‐calculus is done using a Web‐services‐based resource locator. The article also describes the pipeline of processing from initial stereo photogrametry to the final production of animation models. A key step in this is the conformation of animators models to the data obtained by the real‐time scanner. Algorithmic innovations in this process are described. Copyright © 2006 John Wiley & Sons, Ltd.

Appropriate use of a probabilistic broadcasting method in MANETs can decrease the number of rebroadcasts, and as a result reduce the opportunity of contention and collision among neighbouring nodes. In this paper we evaluate the performance of Adjusted Probabilistic flooding by comparing it to "simple" flooding as used with the Ad Hoc on Demand Distance Vector (AODV) routing protocol as well as a fixed probabilistic approach. The results reveal that the Adjusted Probabilistic flooding exhibits superior performance in terms of both reachability and saved rebroadcasts.

A major issue in modelling the performance merits of interconnection network is dealing with virtual channels. Some analytical models chose not to deal with this issue at all i.e. one virtual channel per physical channel. More sophisticated models, however, relayed on a method proposed by Dally to capture the effect of arranging the physical channel into many virtual channels. In this study, we investigate the accuracy of Dally's method and propose an alternative approach to deal with virtual channels in analytical performance modelling. The new method is validated via simulation experiments and results reveal its accuracy under different traffic conditions

A number of recent research studies have explored ways to improve TCP throughput in IEEE 802.11 mobile ad hoc networks. In particular, hidden terminal effects caused by interference have been shown to degrade TCP performance and have been dealt with, in previous work, by restricting the maximum congestion window size. We have pursued an alternative approach and have developed a TCP variant which adjusts the sending rate increase to achieve competitive goodput for TCP connections. In this paper, we demonstrate that a slower sending rate increase during the congestion avoidance phase of TCP leads to improved performance for TCP Reno while eliminating the negative effects inherent in restricting the maximum congestion window size. A performance comparison against existing solutions under various mobility conditions is also included.

Abstract Several studies have examined the relative performance merits of the torus and hypercube taking into account the channel bandwidth constraints imposed by implementation technology. While the torus has been shown to outperform the hypercube under the constant wiring density constraint, the opposite conclusion has been reached when the constant pin‐out constraint is considered. However, these studies have assumed a pure uniform traffic pattern and deterministic routing. The ‘uniform traffic’ assumption is not always justifiable in practice as there are many real‐world parallel applications that exhibit non‐uniform traffic patterns, which can create unbalanced traffic such as hotspots in the network. This paper re‐examines the performance merits of the torus and hypercube in the presence of hotspot traffic. The comparative analysis is based on fully adaptive routing as this has been gaining popularity in recent practical multicomputers. Moreover, it uses a new cost model that takes into account the implementation cost of the network and its routers. The results reveal that for moderate and large system sizes, lower dimensionalk‐aryn‐cubes (e.g. 2D torus) always outperform their higher dimensional counterparts even under the pin‐out constraint. Copyright © 2004 John Wiley & Sons, Ltd.

Analytical models are cost-effective and versatile tools for evaluating system performance under different design alternatives. This study presents an analytical performance model for pipelined circuit switching (PCS) in binary n-cube networks in the presence of bursty traffic, which is modeled by a switched Poisson process (SPP). The validity of the model is demonstrated by comparing analytical results to those obtained through simulation experiments of the actual system. This model and that proposed by Min et al. for wormhole switching (WS) are then used to investigate the relative performance merits of PCS and WS under bursty traffic.

The k-ary n-cube has been used as the underlying topology for most practical multicomputers, and has been extensively studied in the past. We investigate some properties of this network. In particular, we study the problem of finding the number of nodes located i hops away from a given node (surface area) and the number of nodes located within i hops away from a given node (volume) in both the unidirectional and bidirectional k-ary n-cube, and have derived exact expressions calculating these numbers. These results are very useful when studying, for example, the spanning tree structure of the k-ary n-cube and the problem of resource placement in this network.

Several analytical models have been proposed in the literature for wormhole-routed multicomputers. However, all these models have been discussed in the context of unicast communication and there has been comparatively little activity in the area of analytical modelling of collective communication algorithms like broadcast. This paper presents an analytical model for predicting latency of broadcast messages in wormhole-routed hypercubes. Results obtained through simulation experiments show that the model exhibits a good degree of accuracy in predicting broadcast latency under different working conditions.

Several analytical models of fully adaptive routing have recently been proposed for wormhole-routed k-ary n-cubes under the uniform traffic pattern. However, there has been hardly any model reported yet that deals with other important nonuniform traffic patterns, such as hot-spots. As a result, most studies have resorted to simulation when evaluating the performance merits of adaptive routing. In an effort to fill this gap, this paper describes the first analytical model of fully adaptive routing in k-ary n-cubes in the presence of hot-spot traffic. Results from simulation show close agreement with those predicted by the model.

Several analytical models of deterministic routing in wormhole-routed k-ary n-cubes have already been reported in the literature. The performance characteristics of most fully-adaptive routing algorithms have often been analyzed by means of simulation and there is hardly any analytical model proposed for calculating message latency in wormhole-routed k-ary n-cubes using adaptive routing. The paper proposes an accurate analytical model to predict the message latency in wormhole-routed k-ary n-cubes with fully adaptive routing. The proposed model is general in that it exhibits a good degree of accuracy for various network configurations and under different operating conditions.

Several analytical models of fully adaptive routing in wormhole-routed k-ary n-cubes under the uniform traffic pattern have recently been proposed in the literature. Although the uniform reference model has been widely used in the past, it is not always true in practice as there are many applications that exhibit non-uniform traffic patterns. There has not been so far any study that describes an analytical model of fully adaptive routing under permutation traffic patterns. This paper describes a new analytical model of fully adaptive routing in k-ary n-cubes in the presence of non-uniform traffic generated by matrix-transpose permutations, which is an important communication operation found in many matrix computation problems. Results obtained through simulation experiments confirm that the model predicts message latency with a reasonable degree of accuracy under different working conditions.

Several analytical models of fully-adaptive routing have recently been proposed for wormhole-routed k-ary n-cubes under the uniform traffic pattern. However, there has been hardly any model reported yet that deals with other important non-uniform traffic patterns, such as hot spots. As a result, most studies have resorted to simulation when evaluating the performance merits of adaptive routing. This paper describes the first analytical model of fully-adaptive wormhole routing in k-ary n-cubes in the presence of hot spot traffic. Results from simulation show close agreement with those predicted by the model.

This paper introduces a parallel algorithm for computing an N=n!-point Lagrange interpolation on an n-star (n>2). It exploits several communication techniques on stars in a novel way which can be adapted for computing similar functions. The algorithm is optimal and consists of three phases: initialization, main and final. While there is no computation in the initialization phase, the main phase is composed of n!/2 steps, each consisting of four multiplications, four subtractions and one communication operation, and an additional step including one division and one multiplication. The final phase is carried out in (n-1) sub-phases each with O(log n) steps where each step takes three communications and one addition.

Many analytical models of wormhole-routed networks have been proposed over the past few years. Most of these models, however, have been developed for unicast (or point-to-point) communication. There has been comparatively little activity in the area of analytical models of collective communication, such as broadcast. As a result, most existing studies have relied on simulation to evaluate the performance merits of collective communication algorithms. This paper presents a new analytical model for predicting broadcast latency in the hypercube. Results obtained through simulation experiments show that the model exhibits a good degree of accuracy in predicting message latency under different working conditions.

Several analytical models of adaptive routing in wormhole-routed networks, including hypercubes, under the uniform traffic pattern have recently been proposed in the literature. However, there has been hardly any model reported yet that deals with other important non-uniform traffic patterns exhibited by many parallel applications. As a result, most existing studies have resorted to simulation when evaluating the performance merits of adaptive routing under non-uniform traffic conditions. This paper describes a new analytical model of adaptive routing in the hypercube in the presence of non-uniform traffic generated by matrix-transpose permutations, which is used in many matrix computation problems. Results obtained through simulation experiments show that the model exhibits a good degree of accuracy in predicting message latency under different working conditions.

Low-dimensional k-ary n-cubes have been popular in recent multicomputers. These networks, however, suffer from high switching delays due to their high message distance. To overcome this problem, Dally has proposed a variation, called express k-ary n-cubes. with express channels that allow non-local messages to partially bypass clusters of nodes within a dimension. K-ary n-cubes are graph topologies where a channel connects exactly two nodes. This study argues that hypergraph topologies, where a channel connects any number of nodes, thus providing total bypasses within a dimension, represent potential candidates for future high-performance networks. It presents a comparative analysis, of a regular hypergraph, referred to as the distributed crossbar switch hypermesh (DCSH), and the express k-ary n-cube. The analysis considers channel bandwidth constraints which apply in different implementation technologies. The results conclude that the DCSH's total bypass strategy yields superior performance characteristics to the partial bypassing of its express cube counterpart.

In a multicomputer network, the channel bandwidth is greatly constrained by implementation technology. Two important constraints have been identified in the literature, each appropriate for a particular technology: wiring density limits dominate in VLSI and pin-out in multiple-chip implementations. Most existing interconnection networks are categorized as either direct or indirect (multi-stage) topologies, the mesh and binary n-cube being examples of the former category, the omega and banyan networks of the latter. This paper argues that direct networks based on hypergraph topologies have characteristics which make them particularly appropriate for use in future high-performance parallel systems. The authors have recently introduced a regular multi-dimensional hypergraph network, called the Distributed Crossbar Switch Hypermesh (DCSH), which has topological properties that permit a relaxation of bandwidth constraints, and which has important topological and performance advantages over direct graph networks. This paper compares the DCSH to multi-stage networks, under both VLSI and multiple-chip technological constraints. The results suggest that in both cases, with a realistic model which includes routing delays through intermediate nodes, the DCSH exhibits superior performance across a wide range of traffic loads.

This paper describes a multiple microprocessor system, under development at Glasgow University, for application to calculations arising in the theory of the Nuclear Shell Model. It is the intention of the authors to discuss the architecture rather than the operation of this machine, and to concentrate particularly on design features which will allow future expansion of both capability and applicability within the range of such computations.