¡@¡@Kademlia[1] provides a concept of using XOR between ID to present logical distance. As Kademlia uses logical distance to search, it cannot take physical distance into consideration, which can lead the result to be the closest in logical, but the farthest in physical. ¡@¡@In this paper, ping rate is used to represent the meaning of physical distance, and construct a physical network in Kademlia. The operations like lookup and search will take logical and physical distance into consideration at the same time, called PRKad. ¡@¡@The simulation result shows that PRKad can actually automatically choose the more efficiency nodes, which means the close nodes in physical network, to decrease the time using of the following operations.

Distributed hash tables (DHTs) have gained much attention from the research community in the last years. Formal analysis and evaluations on simulators and small-scale deployments have shown good scalability and performance. In stark contrast, performance measurements in large-scale DHT overlays on the Internet have yielded disappointing results, with lookup latencies measured in seconds. Others have attempted to improve lookup performance with very limited success, their lowest median lookup latency at over one second and a long tail of high-latency lookups. In this thesis, the goal is to to enable large-scale DHT-based latency-sensitive applications on the Internet. In particular, we improve lookup latency in Mainline DHT, the largest DHT overlay on the open Internet, to identify and address practical issues on an existing system. Our approach is implementing and measuring backward-compatible modifications to facilitate their incremental adoption into Mainline DHT (and possibly other Kademlia-based overlays). Thus, enabling our research to have impact on a real-world system. Our results close the performance gap between small- and large-scale DHT overlays. With a median lookup latency below 200 ms and a 99\superscript{th} percentile of just above 500 ms, our median lookup latency is one order of magnitude lower than the best performing measurement reported in the literature. Moreover, our results do not show a long tail of high-latency lookups, unlike previous reports. We have achieved these results by studying how connectivity artifacts on the underlying network ---probably caused by firewalls and NAT devices on the Internet--- affect the DHT overlay. Our measurements of the connectivity of more than 3 million nodes reveal that connectivity artifacts are widespread and can severely degrade lookup performance. Scalability and locality-awareness have also been explored in this thesis, where different mechanisms have been proposed. Some of the mechanisms are planned to be integrated into Mainline DHT in future work. / QC 20111118

L’agrégation des valeurs qui doivent être gardées confidentielles tout en garantissant la robustesse du processus et l’exactitude du résultat est nécessaire pour un nombre croissant d’applications. Divers types d’enquêtes, telles que les examens médicaux, les référendums, les élections, ainsi que les nouveaux services de Internet of Things, tels que la domotique, nécessitent l’agrégation de données confidentielles. En général,la confidentialité est assurée sur la base de tiers de confiance ou des promesses de cryptographie, dont les capacités ne peuvent être évaluées sans expertise.L’ambition de cette thèse est de réduire le besoin de confiance dans les autorités, de même que la technologie, et d’explorer les méthodes d’agrégations de données à grande échelle, qui garantissent un degré élevé de confidentialité et ne dépendent ni de tiers de confiance ni de cryptographie. Inspiré par BitTorrent et Bitcoin, les protocoles P2P sont considérés. La première contribution de cette thèse est l’extension du protocole d’agrégation distribuée BitBallot dans le but de couvrir les agrégations dans les réseaux P2P comprenant des pairs adversaires avec un comportement défaillant ou byzantin. Les changements introduits permettent éventuellement de maintenir un résultat précis en présence d’une minorité adversaire. Les limites de scalabilité rencontrées conduisent à la deuxième contribution dans le but de soutenir les agrégations à grande échelle. Inspiré par BitBallot et BitTorrent, un nouveau protocole distribué appelé ADVOKAT est proposé.Dans les deux protocoles, les pairs sont affectés aux noeuds feuilles d’un réseau de superposition d’une structure arborescente qui détermine le calcul des agrégats intermédiaires et restreint l’échange de données. La partition des données et du calcul entre un réseau de pairs équipotent limite le risque de violation de données et réduit le besoin de confiance dans les autorités. Les protocoles fournissent une couche middleware dont la flexibilité est démontrée par les applications de vote et de loterie. / Aggregation of values that need to be kept confidential while guaranteeing the robustness of the process and the correctness of the result is necessary for an increasing number of applications. Various kinds of surveys, such as medical ones, opinion polls, referendums, elections, as well as new services of the Internet of Things, such as home automation, require the aggregation of confidential data. In general, the confidentiality is ensured on the basis of trusted third parties or promises of cryptography, whose capacities cannot be assessed without expert knowledge.The ambition of this thesis is to reduce the need for trust in both authorities and technology and explore methods for large-scale data aggregations, that ensure a high degree of confidentiality and rely neither on trusted third parties nor solely on cryptography. Inspired by BitTorrent and Bitcoin, P2P protocols are considered.The first contribution of this thesis is the extension of the distributed aggregation protocol BitBallot with the objective to cover aggregations in P2P networks comprising adversarial peers with fail-stop or Byzantine behaviour. The introduced changes allow eventually to maintain an accurate result in presence of an adversarial minority.The encountered scalability limitations lead to the second contribution with the objective to support large-scale aggregations. Inspired by both BitBallot and BitTorrent, a novel distributed protocol called ADVOKAT is proposed.In both protocols, peers are assigned to leaf nodes of a tree overlay network which determines the computation of intermediate aggregates and restricts the exchange of data. The partition of data and computation among a network of equipotent peers limits the potential for data breaches and reduces the need for trust in authorities. The protocols provide a middleware layer whose flexibility is demonstrated by voting and lottery applications.

Apresenta-se o resultado de uma pesquisa destinada a propor um serviço para a resolução e descoberta de informações sobre objetos. Neste contexto, entendem-se como objetos os itens de uma cadeia produtiva e, como prováveis clientes do serviço proposto, sistemas de informação destinados ao gerenciamento de logística junto às cadeias produtivas e/ou à manutenção de dados sobre a rastreabilidade das cadeias. Encontram-se no mercado diversos sistemas de informação com estas características. A conveniência da troca de informações diretas entre os membros das cadeias produtivas, motiva diversos pesquisadores a propor a criação de padrões de dados. Uma das propostas mais relevantes, apresentada pela entidade internacional GS1, envolve a especificação de uma arquitetura para estes sistemas, bem como um vocabulário de dados padronizado, a Rede EPCglobal®. A utilização da tecnologia RFID permite a obtenção automática de dados, quando da passagem dos itens por leitores RFID instalados ao longo da cadeia produtiva. A utilização de um código padronizado, denominado Electronic Product CodeTM (EPC) na gravação das etiquetas RFID é outra vantagem desta tecnologia. Uma das funcionalidades essenciais deste sistema consiste na possibilidade de obtenção de informações relativas a um determinado produto. Estas informações podem se encontrar não somente no produtor do item, mas em todos os membros da cadeia produtiva que tiveram acesso ao item. Esta funcionalidade é o único aspecto da rede EPCglobal® ainda não especificada pelo GS1. Por esta razão, diversos pesquisadores têm-se dedicado à elaboração de propostas. O resultado desta pesquisa é mais uma delas. A solução apresentada baseia-se no uso de redes peer-to-peer (P2P), mais especificamente do protocolo Kademlia, escolhido a partir da comparação entre os vários protocolos propostos na literatura, visando a uma melhor eficácia. A partir de uma simulação efetuada em software especialmente desenvolvido para esta finalidade, apresentam-se os detalhes da sugestão e os resultados obtidos com sua utilização. / This is the result of a survey intended to propose a resolution and discovery service of information about objects. In this context, objects are items of a production chain and, likely customers of the proposed service, are information systems intended for logistics management at the productive chains and/or maintenance of data on traceability of supply chains. This scenario fits perfectly to the paradigm of the Internet of Things, where objects of everyday use have active participation on the Internet. The convenience of direct exchange of information between the members and the supply chains motivates many researchers to propose the creation of data standards. One of the most relevant proposals, presented by the international organization GS1, involves the architecture specification for these systems, as well as a standard data vocabulary, the EPCglobal® Network. The use of RFID technology allows obtaining data, during the passage of items by RFID readers installed along the supply chain. The use of a standardized code in the recording of RFID tags, called the Electronic Product CodeTM (EPC), is another advantage of this technology. One of the essential features of this system is the possibility of obtaining information relating to an individual product. This information can be found not only in item producer, but also in all members of the supply chain that had access to the item. This functionality is the only aspect of EPCglobal® not yet specified by GS1. For this reason, several researchers have been working with new suggestions. The solution presented is another proposal based on the use of an implementation of a peer-to-peer (P2P) network, using the Kademlia Protocol, chosen from the comparison between the several protocols proposed in the literature, aiming at a better effectiveness. From a simulation carried out in software specially developed for this purpose, we present the details of the suggestion and the results obtained with its use.

Apresenta-se o resultado de uma pesquisa destinada a propor um serviço para a resolução e descoberta de informações sobre objetos. Neste contexto, entendem-se como objetos os itens de uma cadeia produtiva e, como prováveis clientes do serviço proposto, sistemas de informação destinados ao gerenciamento de logística junto às cadeias produtivas e/ou à manutenção de dados sobre a rastreabilidade das cadeias. Encontram-se no mercado diversos sistemas de informação com estas características. A conveniência da troca de informações diretas entre os membros das cadeias produtivas, motiva diversos pesquisadores a propor a criação de padrões de dados. Uma das propostas mais relevantes, apresentada pela entidade internacional GS1, envolve a especificação de uma arquitetura para estes sistemas, bem como um vocabulário de dados padronizado, a Rede EPCglobal®. A utilização da tecnologia RFID permite a obtenção automática de dados, quando da passagem dos itens por leitores RFID instalados ao longo da cadeia produtiva. A utilização de um código padronizado, denominado Electronic Product CodeTM (EPC) na gravação das etiquetas RFID é outra vantagem desta tecnologia. Uma das funcionalidades essenciais deste sistema consiste na possibilidade de obtenção de informações relativas a um determinado produto. Estas informações podem se encontrar não somente no produtor do item, mas em todos os membros da cadeia produtiva que tiveram acesso ao item. Esta funcionalidade é o único aspecto da rede EPCglobal® ainda não especificada pelo GS1. Por esta razão, diversos pesquisadores têm-se dedicado à elaboração de propostas. O resultado desta pesquisa é mais uma delas. A solução apresentada baseia-se no uso de redes peer-to-peer (P2P), mais especificamente do protocolo Kademlia, escolhido a partir da comparação entre os vários protocolos propostos na literatura, visando a uma melhor eficácia. A partir de uma simulação efetuada em software especialmente desenvolvido para esta finalidade, apresentam-se os detalhes da sugestão e os resultados obtidos com sua utilização. / This is the result of a survey intended to propose a resolution and discovery service of information about objects. In this context, objects are items of a production chain and, likely customers of the proposed service, are information systems intended for logistics management at the productive chains and/or maintenance of data on traceability of supply chains. This scenario fits perfectly to the paradigm of the Internet of Things, where objects of everyday use have active participation on the Internet. The convenience of direct exchange of information between the members and the supply chains motivates many researchers to propose the creation of data standards. One of the most relevant proposals, presented by the international organization GS1, involves the architecture specification for these systems, as well as a standard data vocabulary, the EPCglobal® Network. The use of RFID technology allows obtaining data, during the passage of items by RFID readers installed along the supply chain. The use of a standardized code in the recording of RFID tags, called the Electronic Product CodeTM (EPC), is another advantage of this technology. One of the essential features of this system is the possibility of obtaining information relating to an individual product. This information can be found not only in item producer, but also in all members of the supply chain that had access to the item. This functionality is the only aspect of EPCglobal® not yet specified by GS1. For this reason, several researchers have been working with new suggestions. The solution presented is another proposal based on the use of an implementation of a peer-to-peer (P2P) network, using the Kademlia Protocol, chosen from the comparison between the several protocols proposed in the literature, aiming at a better effectiveness. From a simulation carried out in software specially developed for this purpose, we present the details of the suggestion and the results obtained with its use.

Among malicious codes like computer viruses and worms, botnets have attracted a significant attention and have been one of the biggest threats on the Internet. Botnets have evolved to incorporate peer-to-peer communications for the purpose of propagating instructions to large numbers of computers (also known as bot) under the botmaster's control. The impact of the botnet lies in its ability for a bot master to execute large scale attacks while remaining hidden as the true director of the attack. One such recently known botnet is the Storm botnet. Storm is based on the Overnet Distributed Hash Table (DHT) protocol which in turn is based on the Kademlia DHT protocol. Significant research has been done for determining its operational size, behaviour and mitigation approaches. In this research, the peer-to-peer behaviour of Storm is studied by simulating its actual packet level network behaviour. The packet level simulator is developed via the simulation framework OMNET++ to determine the impact of design parameters on botnets performance and resilience. Parameters such as botnet size, peer list size, the number of bot masters and the key propagation time have been explored. Furthermore, two mitigation strategies are considered: a) random removal strategy (disinfection strategy), that removes selected bots randomly from the botnet; b) Sybil disruption strategy, that introduces fake bots into the botnet with the task of propagating Sybil values into the botnet to disrupt the communication channels between the controllers and the compromised machines. The simulation studies demonstrate that Sybil disruption strategies outperform random removal strategies. The simulation results also indicate that random removal strategies are not even effective for a small sized networks. The results of the simulation studies are particularly applicable to the Storm botnet but these results also provide insights that can be applied to peer-to-peer based botnets in general.

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