Abstract not available

One of the activities of most successful intruders of a computer system is to modify data on the victim,either to hide his/her presence and to destroy the evidence of the break-in, or to subvert the system completely and make it accessible for further abuse without triggering alarms.File integrity checking is one common method to mitigate the effects of successful intrusions by detecting the changes an intruder makes to files on a computer system. Historically file integrity checking has been implemented using tools that operate locally on a single system, which imposes quite some restrictions regardingmaintenance and scalability. Recent improvements for large scale environments have introduced trusted central servers which provide secure fingerprint storage and logging facilities, but such centralism presents some new shortcomings.This thesis describes an alternative, decentralised approach where peer-to-peer mechanisms are used to provide fingerprint storage for file integrity checking with more flexibility and scalability than offered by currently available systems. A research implementation has been developed to verify the approach as viable and practical, and experimental results obtained with that prototype are discussed.

University of Technology, Sydney. Faculty of Information Technology. / Over the last few years Peer-to-Peer (P2P) systems have emerged as highly attractive systems supporting many useful large-scale applications and services. They allow the exploitation of enormous untapped resources (such as idle processing cycles, storage, and bandwidth) available at Internet-connected devices, which were previously considered incapable of providing services to others. Participating nodes (peers) form an overlay network and communicate with each other without being controlled by a central authority. The structures and routing decisions of the most current P2P networks often do not correlate with the Internet infrastructure. In doing so, the tasks of overlay construction and routing become less complicated however, this results in high end-to-end delay for the P2P applications. As a consequence, the P2P networks may not be able to provide stringent Quality of Service (QoS) requirements for a new generation of P2P applications, and thus limit their benefits for the end users. Moreover, the infrastructure ignorance means P2P systems waste Internet resources by adding more than they should to the Internet traffic. This leads to the increase in Internet access costs substantially, and in turn the P2P systems do not scale well. The thesis presents a novel architecture for developing efficient P2P systems, and new schemes for constructing infrastructure-aware overlay networks. The main objective is first, to overcome the disparity between the overlay and Internet structures in order to maximize the use of network resources and reduce the overlay delay to the P2P applications; second, to provide efficient communication for P2P systems enabling deployment of any P2P applications while preserving decentralized, self-organizing and self-maintaining characteristics for the systems. To achieve these goals, we firstly developed Geographically Longest Prefix Matching (Geo-LPM) and Geographical Partitioning (Geo-Partitioning) schemes to cluster nodes that are close to each other in terms of network latency and network membership, and to determine links between neighboring clusters respectively. The developed schemes are efficient, generate low overhead, and help to produce excellent physically/infrastructure-aware overlay networks. Their distinctive features are self-organization, self-maintenance, and decentralization, which make them suitable to work in a P2P environment. Secondly we propose a novel architecture, called a physically-aware reference model (PARM) that captures desirable features for P2P systems by resolving major functional P2P system problems efficiently in a layered structure. For example, the application routing layer of PARM deals with routing inefficiency, meanwhile the infrastructure unawareness is resolved at the overlay network layer. We develop a useful P2P application, called a Peer Name Service (PNS) that interprets node names into their current IP addresses for any Internet-connected devices. Using the overlay networks, the PNS can support devices, which could be unreachable via the Domain Name Server (DNS), and mobile devices on-the-move without prior setup requirement in a distributed and timely fashion. Finally, to validate the whole concept of PARM, we simulate the PNS and a file transfer to a mobile node at the top layer of PARM, the P2P application layer. Since the PNS is sensitive to delay, it would be useful to evaluate the impacts of overlay delay factor and PARM on the performance of P2P applications. The simulation results show that the performance of the PARM-based applications is significantly improved while achieving decentralized and self-organizing features. The results also indicate that PARM can be a recommended reference model for developing scalable and efficient P2P systems.

This thesis investigates an innovative framework and process coordination technologies for peer-to-peer based decentralised workflow systems. The aim of this work is to address some of the unsolved problems in the contemporary workflow research rudimentally from an architectural viewpoint. The problems addressed in this thesis, i.e., bad performance, vulnerability to failures, poor scalability, user restrictions, unsatisfactory system openness, and lack of support for incompletely specified processes, have become major obstacles for wide deployment of workflow in real-world. After an in-depth analysis of the above problems, this thesis reveals that most of these problems are mainly caused by the mismatch between application nature, i.e., distributed, and system design, i.e., centralised management. Thus, the old-fashioned client-server paradigm which is conventionally used in most of today�s workflow systems should be replaced with a peer-to-peer based, open,collaborative and decentralised framework which can reflect workflow�s distributed feature more naturally. Combining workflow technology and peer-to-peer computing technology, SwinDeW which is a genuinely decentralised workflow approach is proposed in this thesis. The distinguished design of SwinDeW removes both the centralised data repository and the centralised workflow engine from the system. Hence, workflow participants are facilitated by automated peers which are able to communicate and collaborate with one another directly to fulfil both build-time and run-time workflow functions. To achieve this goal, an innovative data storage approach, known as �know what you should know�, is proposed, which divides a process model into individual task partitions and distributes each partition to relevant peers properly according to the capability match. Based on such a data storage approach, the novel mechanisms for decentralised process instantiation, instance execution and execution monitoring are explored. Moreover, SwinDeW is further extended to support incompletely-specified processes in the decentralised environment. New technologies for handling incompletely-specified processes at run-time are presented. The major contributions of this research are an innovative, decentralised workflow system framework and corresponding process coordination technologies for system functionality. Issues regarding system performance, reliability, scalability,user support, system openness, and incompletely-specified process support are discussed deeply. Moreover, this thesis also contributes the SwinDeW prototype which implements and demonstrates this design and functionality for proof-of concept purposes. With these outcomes, performance bottlenecks in workflow systems are likely to be eliminated whilst increased resilience to failure, enhanced scalability, better user support and improved system openness are likely to be achieved with support for both completely- and incompletely-specified processes. As a consequence, workflow systems will be expected to be widely deployable to real world applications to support processes, which was infeasible before.

Cette thèse s'inscrit dans le domaine de l'expérimentation sur les systèmes distribués, et en particulier de leur test ou de leur validation. À côté des méthodes d'évaluation classiques (modélisation, simulation, plates-formes d'expérimentation comme PlanetLab ou Grid'5000) les méthodes basées sur l'émulation et la virtualisation proposent une alternative prometteuse. Elles permettent d'exécuter l'application réelle à étudier, en lui présentant un environnement synthétique, correspondant aux conditions d'expérience souhaitées : il est ainsi possible, à moindre coût, de réaliser des expériences dans des conditions expérimentales différentes, éventuellement impossibles à reproduire dans un environnement réel. Mais l'utilisation de tels outils d'émulation ne peut se faire sans répondre à des questions sur leur réalisme et leur passage à l'échelle. Dans ce travail, nous utilisons une démarche incrémentale pour construire une plate-forme d'émulation destinée à l'étude des systèmes pair-à-pair à grande échelle. Nous commençons par comparer les différentes solutions d'émulation logicielle de liens réseaux, puis illustrons leur utilisation, notamment en étudiant une application réseau complexe : TUNS, un tunnel IP sur DNS. Nous construisons ensuite notre plate-forme d'émulation, P2PLab, en utilisant l'un des émulateurs réseaux précédemment étudiés, ainsi qu'un modèle de topologies réseaux adapté à l'étude des systèmes pair-à-pair. Nous y proposons une solution légère de virtualisation, permettant un bon rapport de repliement (grand nombre de noeuds émulés sur chaque machine physique). Après avoir validé cette plate-forme, nous l'utilisons pour étudier le protocole de diffusion de fichiers pair-à-pair BitTorrent à l'aide d'expériences mettant en jeu près de 15000 noeuds participants.

Les systèmes pair-à-pair permettent de concevoir des systèmes de très grande taille à forte disponibilité, tout cela à faible coût. Au contraire des clients dans un système client-serveur, les pairs d'un réseau pair-à-pair jouent un rôle actif dans le fonctionnement du réseau et fournissent leur bande passante, leur puissance de calcul et leur capacité de stockage : la présence de pairs malveillants ou ne se conformant pas au comportement attendu peut rompre le service proposé. L'obtention de propriétés de sécurité dans un réseau pair-à-pair pose de nouveaux problèmes car, au contraire des systèmes actuels dans lesquels, le plus souvent, une autorité ponctuelle autorise ou non les opérations demandées, aucun pair ne doit avoir un rôle critique pour le système entier. La contribution principale de cette thèse est une autorité de certification distribuée qui permet la signature distribuée de certificats. Au contraire des autorités de certification centralisées actuellement utilisées, y compris dans des réseaux pair-à-pair, l'autorité que nous proposons est entièrement distribuée dans le réseau pair-à-pair et ce sont les pairs eux-mêmes qui prennent les décisions, par l'accord d'un pourcentage fixé d'entre eux. Nous présentons dans ce mémoire les mécanismes cryptographiques mis en œuvre ainsi que deux applications de cette autorité permettant de limiter l'attaque sybile et de nommer les utilisateurs de manière sécurisée.

<p>Advances in peer-to-peer overlay networks and Semantic Web technology will have a substantial influence on the design and implementation of future digital libraries. However, it remains unclear how best to combine their advantages in constructing digital library systems. This thesis is devoted for investigating, proposing and evaluating possible solutions to advance developments in this field.</p><p>The main research goal of this work is to combine the strengths of both peer-to-peer overlay networks and Semantic Web for facilitating semantic searches in large-scale distributed digital library systems. The approach has been conducted in a sequential and progressive manner. Firstly, we recognize system infrastructure and metadata heterogeneity as two major challenges in conducting semantic searching across distributed digital libraries. Next, we investigate the strengths and weaknesses of both peer-to-peer and Semantic Web technology and justify that these two fields are complementary and can be combined in conducting semantic searches in a large-scale distributed environment. Thirdly, due to various topologies, functionalities and limitations different peer-to-peer infrastructures may possess, we survey current classical peer-to-peer systems so as to facilitate determinating appropriate infrastructure for specific application scenario. Fourthly, we probe into approaches in generating ontology-enriched metadata records for semantic search purpose. Finally and most importantly, we will propose a semantic search process for interoperation among heterogeneous resources, basing on ontology mapping mechanism.</p><p>A major contribution expected in our work is, in a broader term, proposing and investigating possible solutions in combining the strengths of both peer-to-peer overlay networks and Semantic Web for facilitating semantic search among highly distributed digital libraries. From a specific perspective, we provide an appropriate benchmark for facilitating decision making in choosing appropriate peer-to-peer networks for digital library construction; especially, we consider in this work no global schema exists and further justify the feasibility and advantages of ontology engineering method in semantic enriched metadata management; to support federated search in such a distributed environment, we also propose an extended super-peer network model, emphasizing in load-balancing and self-organizing capabilities; Based on semantic enriched metadata management, we propose also direct ontology mapping method to enable runtime semantic search process. Evaluation results have illustrated the feasibility and robustness of our approaches.</p><p>The future direction of this work includes studies on user authentication,efficient ontology parsing and real-life applications.</p>

<p>All utveckling av ny teknologi åtföljs av nya möjligheter, framkallar nya aktiviteter, intentioner och återuppväcker idéer som tidvis kolliderar med kraftfulla kommersiella intressen och lagar. Fildelning är i den bemärkelsen ett ytterst intressant och aktuellt exempel. I följande uppsats överträds den offentliga debatten om fildelning, vad vi istället avser är att belysa området utifrån filbytarens perspektiv. Vad vi avser är att studera filbytarens inställningar, motiveringar och värderingar för att därigenom försöka kasta ett nytt ljus över fildelningsfrågan. Empiriskt material som behandlas i studien, har insamlats genom strukturerade enkätintervjuer samt tre personliga intervjuer. Urvalet för undersökningen har huvudsakligen framtagits genom en direkt subjektiv urvalsprocess, vi har helt enkelt uppsökt personer som vi vet ägnar sig åt fildelning. Analysen av undersökningsresultaten underbyggs av Siva Vaidhyanathans teorier om fildelningens kulturella och ideologiska aspekter. Resultatet av följande undersökning tyder på att fildelning ger tillgång till ett bredare utbud av kulturprodukter och att aktiviteten i viss mån också bidrar till att filbytare utvecklar nya intressen. Priserna på kulturprodukter som film och musik, framfördes som en motivering till nerladdning av upphovsrättsskyddat material. Fildelning beskrevs som en reaktion mot missförhållanden i den kommersiella marknaden, eller som ett uttryck för idén om gemensam tillgång till kultur. </p>

In many distributed applications, end hosts need to know the network locations of other nearby participating hosts in order to enhance overall performance. Potential applications that can benefit from the location information include automatic selection of nearby Web servers, proximity routing in a peer-to-peer system, and loss recovery in reliable multicasting. We focus in this paper on the network neighborhood discovery problem in large-scale distributed systems. In these systems, the number of participating nodes can be very large, and the membership can dynamically change. Our goal is for each node to discover other "nearby" participating nodes in a completely decentralized manner, where each node probes only a small subset of other nodes in the system. This approach will lead to improved overall performance by matching client requests for services with participants in the peer-to-peer service system that are, on average, nearby in the network sense. Recent works in distributed peer-to-peer systems, such as Chord, CAN, Tapestry and Pastry, provide efficient distributed lookup structures. In this paper, we investigate a rendezvous-based scheme for a node to discover other nearby participating nodes using a peer-to-peer lookup system such as Chord. Given a key, the Chord protocol maps the key onto a node. Our idea for network neighborhood discovery is for each host to compute a key that characterizes its network location on the Internet. We call such a key the location key, and the nodes that these location keys are mapped to the Rendezvous Points. To lookup other nearby participating nodes, a node seeking some service queries its corresponding rendezvous point using its location key. We focus on the issue of how to generate the location key in a distributed fashion such that nodes that are close to each other in the actual network will have similar location key values, and therefore be mapped to nearby locations on the Chord ring. In this paper, we examine the performance tradeoffs of such a rendezvous scheme using the Global Network Positioning (GNP) approach to generate the location keys. In GNP, each node measures its network distances to a few landmark nodes to derive its coordinates in a D-dimensional geometric space. We generate a host's Chord location key from its 1-dimensional GNP coordinate, and use coordinates from a higher dimensional space to refine the searching process for the closest node. We evaluate our scheme in the context of the nearest neighbor discovery problem. Using data from the Active Measurement Project of the National Laboratory for Applied Network Research (NLANR), we compare its performance with a random mapping scheme, where location keys are randomly generated. Using our coordinate-based rendezvous scheme, 66% of the nodes found their actual closest network neighbor by pinging only a small number of nodes. / Singapore-MIT Alliance (SMA)

In this talk, we will present the design and evaluation of PeerDB, a peer-to-peer (P2P) distributed data sharing system. PeerDB distinguishes itself from existing P2P systems in several ways. First, it is a full-fledge data management system that supports fine-grain content-based searching. Second, it facilitates sharing of data without shared schema. Third, it combines the power of mobile agents into P2P systems to perform operations at peers' sites. Fourth, PeerDB network is self-configurable, i.e., a node can dynamically optimize the set of peers that it can communicate directly with based on some optimization criterion. / Singapore-MIT Alliance (SMA)