Private Information Retrieval (PIR) protocols enable a client to access data from a server without revealing what data was accessed. The study of Computational Private Information Retrieval (CPIR) protocols, an area of PIR protocols focusing on computational security, has been a recently reinvigorated area of focus in the study of cryptography. However, CPIR protocols still have not been utilized in any practical applications. The aim of this thesis is to determine whether the Melchor Gaborit CPIR protocol can be successfully utilized in a practical manner in an anonymous peer-to-peer environment.

O protocolo BitTorrent é uma das aplicações P2P mais bem sucedidas da Internet, sendo largamente estudada pela comunidade de pesquisa. Contudo, o estudo da dinâmica de uma rede BitTorrent de larga escala apresenta diversos desafios, tais como a dificuldade em realizar capturas da rede ou montar experimentos para medição. O método utilizado para superar estes desafios é a simulação, porém não há uma ferramenta adequada disponível para a comunidade de pesquisa. Por conta disso, a maioria dos trabalhos que utilizam simulação desenvolvem os seus próprios simuladores, resultando em trabalhos que não podem ser repetidos ou verificados. Neste trabalho, é apresentado o simulador de BitTorrent EbitSim, que permite a alteração dos mecanismos utilizados, a configuração dos parâmetros do sistema e a definição da topologia utilizada. O simulador foi desenvolvido utilizando o arcabouço OMNeT++, que fornece um conjunto de ferramentas que facilitam a configuração de variados cenários e dos parâmetros do modelo. Além disso, o arcabouço INET foi utilizado para modelar as camadas inferiores de rede. O desenvolvimento do modelo do BitTorrent foi baseado na especificação oficial, e contou com o auxilio de trabalhos relacionados e discussões com desenvolvedores de clientes BitTorrent. O EbitSim foi validado por meio de comparações com resultados obtidos a partir de uma implementação real de uma rede BitTorrent, realizada em um ambiente de testes controlado. Foi demonstrado que o EbitSim apresenta resultados compatíveis com uma rede BitTorrent real. / The BitTorrent protocol is one of the most successful P2P applications, being largely studied by the research community. Nevertheless, studying the dynamics of a large BitTorrent network presents several challenges, such as difficulty in acquiring network traces or building measurement experiments. The simulation method is capable of overcoming these challenges, but there is not an adequate simulation tool available for the research community. This thesis presents the EbitSim BitTorrent Simulator, which is capable of modifying the utilized mechanisms, configuring the systems parameters and defining the topology used in the simulations. The simulator was developed using the OMNeT++ framework, which provides a set of tools that facilitates the configuration of diversified scenarios and the parameters of the model. In addition, the INET framework was utilized to accurately model the lower network levels. We developed the BitTorrent model based on the official specification, with the aid of related works and discussions with developers of BitTorrent client programs. The EbitSim Simulator was validated by performing comparisons with results obtained from a real implementation of a BitTorrent network, deployed in a controlled testbed. We show that the EbitSim Simulator generates results compatible with a real BitTorrent network.

Hermes é um arcabouço para a programação de aplicações P2P. Com ele, pode-se criar diversos tipos de aplicações distribuídas, sem se preocupar com a camada de comunicação. O Hermes não é uma implementação de uma rede de sobreposição P2P, e sim uma camada acima das implementações já existentes. O desenvolvedor da aplicação fica isolado da implementação da rede de sobreposição utilizada. Esse isolamento é feito de forma tal que não há limitações quanto à arquitetura de rede utilizada pela implementação, seja ela centralizada, descentralizada, distribuída estruturada ou distribuída não-estruturada. Entre os serviços oferecidos pelo Hermes estão: troca de mensagens, busca, comunicação em grupo e armazenamento distribuído. Geralmente, no início do desenvolvimento de uma aplicação distribuída, tem-se poucas informações sobre o seu tamanho final ou perfil de utilização. O Hermes possibilita ao desenvolvedor da aplicação adiar, até o momento da efetiva implantação do sistema, a decisão sobre qual arquitetura de rede ou qual implementação de rede de sobreposição são as mais apropriadas para suas necessidades. Possibilita também, quando o perfil de utilização muda com o tempo, a troca da implementação utilizada por uma outra que se adeque mais ao novo perfil sem alterações no código da aplicação. / Hermes is a framework for P2P application programming. Using it, one can create several kinds of distributed applications without worrying about the underlying network. Hermes is not a P2P overlay network implementation, but a shell envolving existing implementations. The application developer is isolated from the implementation of the overlay network in use. This isolation is done in a way that poses no limitations on the network architecture used, which may be centralized, decentralized, structured or unstructured. Amongst the services offered by Hermes are: message exchange, search, group communication, and distributed storage. In the early stages of the development of a distributed application, information as to its final size or utilization profile is often unknown. Hermes gives the application developer the possibility of delaying, until the actual moment of system deployment, the decision as to which network architecture or which overlay network implementation is the most appropriate. It also gives the developer the choice, when utilization profile changes over time, of replacing the network implementation with one more suitable to the application needs, without changes on the application code.

Made available in DSpace on 2015-03-05T13:56:57Z (GMT). No. of bitstreams: 0 Previous issue date: 14 / Nenhuma / Aplicações Peer-to-Peer (P2P) vêm ganhando espaço em ambientes acadêmicos e, sobretudo, corporativos. Nesses ambientes, a ampla adoção de tais aplicações está condicionada ao atendimento de diversos requisitos de segurança, como autenticação, con-fidencialidade e autorização. Existem algumas soluções que buscam suprir necessidades isoladas de segurança, mas possuem a desvantagem de não poderem ser usadas de maneira integrada e exigirem do usuário e do programador das aplicações a manipulação de uma interface de programação complexa, seguida de uma configuração exaustiva. Esta disser tação apresenta uma arquitetura de segurança que isola da aplicação P2P e do middleware de comunicação subjacente a implementação e a configuração dos aspectos de segurança. Esses são atendidos através de módulos isolados que implementam técnicas de segurança já consolidadas. A arquitetura foi implementada tendo como base JXTA, um middleware P2P bastante disseminado. Como estudo de caso, a arquitetura foi incorporada ao Our-Gri / Peer-to-peer (P2P) applications are becoming increasingly important in academic environments and, in particular, corporative ones. In such environments, the wide adop- tion of P2P applications is subject to the fulfilment of several security requirements, including authentication, confidentiality, and authorization. There exist approaches that aim to provide specific security needs, but have two disadvantages: cannot be employed integratedly, and require the user/application programmer to manipulate a complex pro- gramming interface, followed by a cumbersome configuring process. This thesis presents a security architecture that isolates from the P2P application and the underlying com- munication middleware the implementation and configuration of security aspects. The latter are achieved through independent modules that implement well-known security techniques. The architecture was implemented using JXTA, a popular P2P middleware. As a study case, the architecture was incorporated to OurGrid, an applicati

Les matériels mobiles actuels, et les téléphones mobiles en particulier, sont équipés de différentes technologies sans fil qui augmentent et diversifient leurs capacités de communication. L’utilisation combinée et efficace de ces technologies offre des possibilités variées et accrues en termes de services et d’applications. Néanmoins elle requiert la réalisation d’analyses fines en matières de sécurité et de choix du mode de communication à utiliser en fonction de critères dépendant du contexte : coût énergétique, coût financier, préférences des entités impliquées, préservation de la vie privée, etc. Cette problématique est apparue comme une question clé au sein du projet Smart Urban Spaces dans le cadre duquel s’inscrit cette thèse. Notre contribution à ce projet est la création d’applications collaboratives qui utilisent de façon appropriée la gamme des technologies sans fil disponibles sur les matériels considérés. En d’autres termes, on cherche à utiliser les moyens de transmission les plus appropriés (au sens des critères indiqués plus haut) que deux ou plusieurs équipements mobiles peuvent utiliser pour réaliser leurs échanges, qui plus est, sans que cela ne nécessite de connaître leurs positions respectives. La transparence de la localisation des cibles devient ainsi une règle. On peut synthétiser la question centrale que nous avons choisie d’étudier de la manière suivante : comment faire communiquer un ensemble de terminaux mobiles (des téléphones portables en particulier) de façon sécurisée en utilisant la technologie la plus adaptée en fonction du contexte ? Notre objectif est de proposer une réponse à cette question en définissant une plate-forme multi-niveaux prenant en compte les différentes technologies disponibles sur les équipements considérés. Il s’agit en particulier d’identifier l’ensemble des éléments à prendre en compte dans la conception de la plate-forme, de les modéliser, de développer des applications de référence et de valider la pertinence des solutions proposées par des tests, ainsi que des évaluations qualitatives et quantitatives. / Current mobile devices, and mobile phones in particular, are equipped with different wireless technologies that increase and diversify their communication capabilities.The combined and effective use of these technologies offers various opportunities in terms of services and applications. However, it requires detailed analysis in terms of security and choice of the communication mean to use according to context-dependent criteria : energy costs, financial costs, preferences of the involved entities, privacy issues, etc. This problem has emerged as a key issue in the Smart Urban Spaces project in which this thesis was carried out. Our contribution to this project is the creation of collaborative applications adequately using the available wireless technologies on the considered equipments. In other words, we try to use the most appropriate communication mean (according to the criteria listed above) that two or more mobile devices can use to perform exchanges (without considering their respective positions). Then, the transparency of targets localization becomes a rule.We can synthesize the central question that we have chosen to study in the following manner : how to allow a set of mobile terminals (mobile phones in particular) to securely communicate using the most appropriate technology depending on the context ? Our goal is to answer this question by defining a multilevel platform taking into account the different technologies available on the considered equipments. It is necessaty to identify the elements to consider in the design of the platform, to model them, to develop reference applications and to validate the relevance of the proposed solutions with qualitative and quantitative evaluations.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / O avanÃo tecnolÃgico na Ãrea de arquiteturas computacionais tem proporcionado o uso de sistemas de computaÃÃo em muitas aplicaÃÃes que ainda nÃo se haviam se beneficiado com esta tecnologia. Em particular, as arquiteturas computacionais distribuÃdas, associadas com a computaÃÃo mÃvel e a comunicaÃÃo mÃvel, alargaram o horizonte de aplicabilidade em grande proporÃÃo. Dentre as aplicaÃÃes que se beneficiaram com estes avanÃos, a Telemedicina desponta com diversas Ãreas mÃdicas fazendo uso desta tecnologia. Por Telemedicina, entende-se a distribuiÃÃo de assistÃncia mÃdica e a colaboraÃÃo do conhecimento mÃdico à distÃncia, por intermÃdio do uso dos atuais meios de comunicaÃÃo. Muitas soluÃÃes propostas para suportar Telemedicina se baseiam na arquitetura Cliente-Servidor. Esta arquitetura apresenta uma baixa confiabilidade pelo fato de contar com um elemento central (Servidor) para prover os serviÃos solicitados. à claro que redundÃncia pode ser incorporada em nÃvel de servidor, mas ao alto preÃo de ter-se que garantir a consistÃncia dos servidores replicados. Nesta dissertaÃÃo, à proposta uma arquitetura computacional peer-to-peer (P2P), que elimina o elemento central encontrado na arquitetura Cliente-Servidor. à discutida a importÃncia de se utilizar esta tecnologia na oferta de serviÃos de assistÃncia mÃdica especializada a distÃncia, propondo um estilo de colaboraÃÃo direto entre mÃdicos, a partir da interligaÃÃo entre equipamentos computacionais. Dentro deste contexto, à apresentada uma soluÃÃo, denominada JMED, que à desenvolvida por meio de uma plataforma de programaÃÃo para o ambiente da computaÃÃo de rede distribuÃda Peer-to-Peer, conhecida por JXTA. JMED foi implementada e sua aplicaÃÃo em Telemedicina foi validada a partir de uma aplicaÃÃo voltada para segunda opiniÃo mÃdica, fazendo uso tanto de sistemas de computadores, como de telefones celulares. / In the last years Research and Development (R&D) in the area of computer systems and communication systems have started a technological revolution which has made it possible to conceive a number of new products, particularly embedded systems, from cell phones to medical equipments. The area which makes use of both technologies above is frequently known as Information Technology (IT). IT has boosted a number of research projects and has established as a research area in its own. Among the applications which have benefited from IT, Telemedicine is one that stands out. Telemedicine is the distribution of medical care, as well as medical knowledge cooperation at distance by using IT. Many solutions proposals to support Telemedicina if base on the architecture Client-Server. This architecture presents low Reliability for the fact to count on a central element (Server) to provide the requested services. It is clearly that redundancy can be incorporated in server level, but to the high price to have itself that to guarantee the consistency of the talked back servers. In this dissertation we propose a communication architecture based on peer-to-peer (P2P) computing, that it decides the problem of the architecture Client-Server. The importance is argued of if to use this technology in offers in the distance of services of specialized medical assistance, considering a direct style of contribution between doctors, from the interconnection between computational equipment. The proposed system, named JMED, was developed using programming platform for distributed P2P computing known as JXTA. JMED was implemented and we showed that is can be used in Telemedicine application by designing an application known as âsecond opinionâ, where computers and cell phones were used as communication stations.

O protocolo BitTorrent é uma das aplicações P2P mais bem sucedidas da Internet, sendo largamente estudada pela comunidade de pesquisa. Contudo, o estudo da dinâmica de uma rede BitTorrent de larga escala apresenta diversos desafios, tais como a dificuldade em realizar capturas da rede ou montar experimentos para medição. O método utilizado para superar estes desafios é a simulação, porém não há uma ferramenta adequada disponível para a comunidade de pesquisa. Por conta disso, a maioria dos trabalhos que utilizam simulação desenvolvem os seus próprios simuladores, resultando em trabalhos que não podem ser repetidos ou verificados. Neste trabalho, é apresentado o simulador de BitTorrent EbitSim, que permite a alteração dos mecanismos utilizados, a configuração dos parâmetros do sistema e a definição da topologia utilizada. O simulador foi desenvolvido utilizando o arcabouço OMNeT++, que fornece um conjunto de ferramentas que facilitam a configuração de variados cenários e dos parâmetros do modelo. Além disso, o arcabouço INET foi utilizado para modelar as camadas inferiores de rede. O desenvolvimento do modelo do BitTorrent foi baseado na especificação oficial, e contou com o auxilio de trabalhos relacionados e discussões com desenvolvedores de clientes BitTorrent. O EbitSim foi validado por meio de comparações com resultados obtidos a partir de uma implementação real de uma rede BitTorrent, realizada em um ambiente de testes controlado. Foi demonstrado que o EbitSim apresenta resultados compatíveis com uma rede BitTorrent real. / The BitTorrent protocol is one of the most successful P2P applications, being largely studied by the research community. Nevertheless, studying the dynamics of a large BitTorrent network presents several challenges, such as difficulty in acquiring network traces or building measurement experiments. The simulation method is capable of overcoming these challenges, but there is not an adequate simulation tool available for the research community. This thesis presents the EbitSim BitTorrent Simulator, which is capable of modifying the utilized mechanisms, configuring the systems parameters and defining the topology used in the simulations. The simulator was developed using the OMNeT++ framework, which provides a set of tools that facilitates the configuration of diversified scenarios and the parameters of the model. In addition, the INET framework was utilized to accurately model the lower network levels. We developed the BitTorrent model based on the official specification, with the aid of related works and discussions with developers of BitTorrent client programs. The EbitSim Simulator was validated by performing comparisons with results obtained from a real implementation of a BitTorrent network, deployed in a controlled testbed. We show that the EbitSim Simulator generates results compatible with a real BitTorrent network.

With the extremely rapid development of the Internet in recent years, emerging peer-to-peer network overlays are meeting the requirements of a more sophisticated communications environment, providing a useful substrate for applications such as scalable file sharing, data storage, large-scale multicast, web-cache, and publish-subscribe services. Due to its design flexibility, peer-to-peer networks can offer features including self-organization, fault-tolerance, scalability, load-balancing, locality and anonymity. As the Internet grows, there is an urgent requirement to understand real-time network performance degradation. Measurement tools currently used are ping, traceroute and variations of these. SNMP (Simple Network Management Protocol) is also used by network administrators to monitor local networks. However, ping and traceroute can only be used temporarily, SNMP can only be deployed at certain points in networks and these tools are incapable of sharing network measurements among end-users. Due to the distributed nature of networking performance data, peer-to-peer overlay networks present an attractive platform to distribute this information among Internet users. This thesis aims at investigating the desirable locality property of peer-to-peer overlays to create an application to share Internet measurement performance. When measurement data are distributed amongst users, it needs to be localized in the network allowing users to retrieve it when external Internet links fail. Thus, network locality and robustness are the most desirable properties. Although some unstructured overlays also integrate locality in design, they fail to reach rarely located data items. Consequently, structured overlays are chosen because they can locate a rare data item deterministically and they can perform well during network failures. In structured peer-to-peer overlays, Tapestry, Pastry and Chord with proximity neighbour selection, were studied due to their explicit notion of locality. To differentiate the level of locality and resiliency in these protocols, P2Psim simulations were performed. The results show that Tapestry is the more suitable peer-to-peer substrate to build such an application due to its superior localizing data performance. Furthermore, due to the routing similarity between Tapestry and Pastry, an implementation that shares network measurement information was developed on freepastry, verifying the application feasibility. This project also contributes to the extension of P2Psim to integrate with GT-ITM and link failures.

<p>Concepts like peer-to-peer networks and distributed computing are not new. They have been available in different forms for a long time. This thesis examines the possibility of merging these concepts. The assumption is that non-centralized peer-to-peer networks can be used for effective sharing of computing resources. While most peer-to-peer systems today concentrate on sharing of data in various forms, this thesis concentrates on sharing of clock cycles instead of files.</p>

Peer-to-peer (P2P) streaming has recently received much research attention, with successful commercial systems showing its viability in the Internet. Despite the remarkable popularity in real-world systems, the fundamental properties and limitations are not yet well understood from a theoretical perspective, as there exists a significant gap between the fundamental limits and the performance achieved in practice. In this thesis, we seek to provide an in-depth analytical understanding of fundamental properties and limitations of P2P streaming systems, with a particular spotlight on the performance gap. We first identify the major problem in existing streaming protocols and show that this problem accounts for most of the gap separating the actual and optimal performances of the streaming systems. We then propose a remedy based on network coding to address this problem and show that the gap to the fundamental limits can be significantly reduced.