As grades computacionais e as redes peer-to-peer (P2P) surgiram como áreas distintas, com diferentes propósitos, modelos e ferramentas. No decorrer dos últimos anos, estas áreas foram convergindo, uma vez que a infraestrutura e o modelo de execução descentralizada das redes P2P provaram ser uma alternativa adequada para o tratamento de questões relacionadas à manutenção de grades de larga escala, tais como escalabilidade, descoberta, alocação e monitoramento de recursos. O modelo MultiCluster trata a convergência entre grades computacionais e redes peer-to-peer de uma forma mais restrita: os problemas de escalabilidade, de descoberta e alocação de recursos são minimizados considerando-se apenas recursos localmente disponíveis para a construção de uma grade, a qual pode ser usada para a execução de aplicações com diferentes características de acoplamento e comunicação. Esse trabalho apresenta a arquitetura do modelo e seus aspectos funcionais, bem como um primeira implementação do modelo, realizada através da adaptação da biblioteca de programação DECK sobre os protocolos do projeto JXTA. A avaliação do funcionamento dessa implementação é apresentada e discutida, com base em algumas aplicações com diferentes características. / Grid computing and peer-to-peer computing emerged as distinct areas with different purposes, models and tools. Over the last years, these areas has been converging since the infrastructure and the execution model used in peer-to-peer networks have proven to be a suitable way to treat some problems related to the maintenance of large scale grids, such as scalability, monitoring, and resource discovery and allocation. The MultiCluster model addresses the convergence of grids and peer-to-peer networks in a more restricted way: the problems related to scalability, resource allocation and discovery are minimized by considering only local resources for the conception of a small scale grid, which can be used to run applications with different characteristics of granularity and communication. This work presents the MultiCluster architecture and its functional aspects, as well as a first implementation carried out by adapting the DECK programming library to use JXTA protocols and its consequent evaluation, based on applications with different characteristics.

As grades computacionais e as redes peer-to-peer (P2P) surgiram como áreas distintas, com diferentes propósitos, modelos e ferramentas. No decorrer dos últimos anos, estas áreas foram convergindo, uma vez que a infraestrutura e o modelo de execução descentralizada das redes P2P provaram ser uma alternativa adequada para o tratamento de questões relacionadas à manutenção de grades de larga escala, tais como escalabilidade, descoberta, alocação e monitoramento de recursos. O modelo MultiCluster trata a convergência entre grades computacionais e redes peer-to-peer de uma forma mais restrita: os problemas de escalabilidade, de descoberta e alocação de recursos são minimizados considerando-se apenas recursos localmente disponíveis para a construção de uma grade, a qual pode ser usada para a execução de aplicações com diferentes características de acoplamento e comunicação. Esse trabalho apresenta a arquitetura do modelo e seus aspectos funcionais, bem como um primeira implementação do modelo, realizada através da adaptação da biblioteca de programação DECK sobre os protocolos do projeto JXTA. A avaliação do funcionamento dessa implementação é apresentada e discutida, com base em algumas aplicações com diferentes características. / Grid computing and peer-to-peer computing emerged as distinct areas with different purposes, models and tools. Over the last years, these areas has been converging since the infrastructure and the execution model used in peer-to-peer networks have proven to be a suitable way to treat some problems related to the maintenance of large scale grids, such as scalability, monitoring, and resource discovery and allocation. The MultiCluster model addresses the convergence of grids and peer-to-peer networks in a more restricted way: the problems related to scalability, resource allocation and discovery are minimized by considering only local resources for the conception of a small scale grid, which can be used to run applications with different characteristics of granularity and communication. This work presents the MultiCluster architecture and its functional aspects, as well as a first implementation carried out by adapting the DECK programming library to use JXTA protocols and its consequent evaluation, based on applications with different characteristics.

O ataque Sybil consiste na criação indiscriminada de identidades forjadas por um usuário malicioso (atacante). Uma abordagem promissora para mitigar esse ataque consiste em conceder novas identidades mediante a resolução de desafios computacionais. Apesar de suas potencialidades, as soluções baseadas em tal abordagem não distinguem solicitações de usuários corretos das de atacantes, fazendo com que ambos paguem o mesmo preço por identidade solicitada. Por conta disso, essas soluções podem não ser efetivas quando os recursos computacionais dos atacantes são muito superiores aos que os usuários legítimos dispõem. Assumindo desafios de uma determinada dificuldade, atacantes com hardware de maior capacidade conseguiriam resolver um conjunto muito superior de desafios e, com isso, obter um número elevado de identidades. Aumentar uniformemente a dificuldade dos desafios poderia, no outro extremo, tornar proibitivo o ingresso de pares a rede. Para lidar com esse problema, nesta dissertação propi5e-se o use de desafios adaptativos como limitante a disseminação de Sybils. Estima-se um grau de confiança da fonte de onde partem as solicitações de identidade em relação as demais. Quanto maior a frequência de solicitação de identidades, menor o grau de confiança e, consequentemente, maior a complexidade do desafio a ser resolvido pelo(s) usuário(s) associado(s) Aquela fonte. Resultados obtidos por meio de experimentação mostram a capacidade da solução de atribuir desafios mais complexos a potenciais atacantes, penalizando minimamente usuários legítimos. / The Sybil attack consists on the indiscriminate creation of counterfeit identities by a malicious user (attacker). An effective approach to tackle such attack consists of establishing computational puzzles to be solved prior to granting new identities. Despite its potentialities, solutions based on such approach do not distinguish between identity requests from correct users and attackers, and thus require both to afford the same cost per identity requested. Therefore, those approaches may not be effective when the attacker's computational resources are superior than those used by correct users. Assuming any choice of puzzle hardness, attackers that have access to high-performance computing resources will be able to solve puzzles several order of magnitude faster than legitimate users and thus obtain a large amount of identities. On the other way, raising the cost to solve the puzzles could restrict legitimate users too much. To tackle this problem, in this paper we propose the use of adaptive computational puzzles to limit the spread of Sybils. We estimate a trust score of the source of identity requests in regard to the behavior of others. The higher the frequency a source requests identities, the lower its trust score and, consequently, the higher the complexity of the puzzle to be solved by the user(s) associated to that source. Results achieved by means of an experimental evaluation evidence our solution's ability to establish more complex puzzles to potential attackers, while minimally penalizing legitimate users.

O ataque Sybil consiste na criação indiscriminada de identidades forjadas por um usuário malicioso (atacante). Uma abordagem promissora para mitigar esse ataque consiste em conceder novas identidades mediante a resolução de desafios computacionais. Apesar de suas potencialidades, as soluções baseadas em tal abordagem não distinguem solicitações de usuários corretos das de atacantes, fazendo com que ambos paguem o mesmo preço por identidade solicitada. Por conta disso, essas soluções podem não ser efetivas quando os recursos computacionais dos atacantes são muito superiores aos que os usuários legítimos dispõem. Assumindo desafios de uma determinada dificuldade, atacantes com hardware de maior capacidade conseguiriam resolver um conjunto muito superior de desafios e, com isso, obter um número elevado de identidades. Aumentar uniformemente a dificuldade dos desafios poderia, no outro extremo, tornar proibitivo o ingresso de pares a rede. Para lidar com esse problema, nesta dissertação propi5e-se o use de desafios adaptativos como limitante a disseminação de Sybils. Estima-se um grau de confiança da fonte de onde partem as solicitações de identidade em relação as demais. Quanto maior a frequência de solicitação de identidades, menor o grau de confiança e, consequentemente, maior a complexidade do desafio a ser resolvido pelo(s) usuário(s) associado(s) Aquela fonte. Resultados obtidos por meio de experimentação mostram a capacidade da solução de atribuir desafios mais complexos a potenciais atacantes, penalizando minimamente usuários legítimos. / The Sybil attack consists on the indiscriminate creation of counterfeit identities by a malicious user (attacker). An effective approach to tackle such attack consists of establishing computational puzzles to be solved prior to granting new identities. Despite its potentialities, solutions based on such approach do not distinguish between identity requests from correct users and attackers, and thus require both to afford the same cost per identity requested. Therefore, those approaches may not be effective when the attacker's computational resources are superior than those used by correct users. Assuming any choice of puzzle hardness, attackers that have access to high-performance computing resources will be able to solve puzzles several order of magnitude faster than legitimate users and thus obtain a large amount of identities. On the other way, raising the cost to solve the puzzles could restrict legitimate users too much. To tackle this problem, in this paper we propose the use of adaptive computational puzzles to limit the spread of Sybils. We estimate a trust score of the source of identity requests in regard to the behavior of others. The higher the frequency a source requests identities, the lower its trust score and, consequently, the higher the complexity of the puzzle to be solved by the user(s) associated to that source. Results achieved by means of an experimental evaluation evidence our solution's ability to establish more complex puzzles to potential attackers, while minimally penalizing legitimate users.

The current state of the industry’s methods of collecting background data reflecting diagnostic and usage information are often opaque and require users to place a lot of trust in the entity receiving the data. For vendors, having a centralized database of potentially sensitive data is a privacy protection headache and a potential liability should a breach of that database occur. Unfortunately, high profile privacy failures are not uncommon, so many individuals and companies are understandably skeptical and choose not to contribute any information. It is a shame, since the data could be used for improving reliability, or getting stronger security, or for valuable academic research into real-world usage patterns. We propose, implement and evaluate a framework for non-realtime anonymous data collection, aggregation for analysis, and feedback. Departing from the usual “trusted core” approach, we aim to maintain reporters’ anonymity even if the centralized part of the system is compromised. We design a peer-to-peer mix network and its protocol that are tuned to the properties of background diagnostic traffic. Our system delivers data to a centralized repository while maintaining (i) source anonymity, (ii) privacy in transit, and (iii) the ability to provide analysis feedback back to the source. By removing the core’s ability to identify the source of data and to track users over time, we drastically reduce its attractiveness as a potential attack target and allow vendors to make concrete and verifiable privacy and anonymity claims.

This document is the final report of the master's thesis "Implementation and Evuation of the Service Peer Discovery Protocol", carried out at the Center for Wireess Systems, KTH, Stockholm. This thesis addresses the problem of service discovery in peer-to-peer mobile networks by implementing and evaluating a previously designed protocl (the Service Peer Discovery Protocol). The main feature of peer-to-peer networks is that users connected to them can communicate directly with each other, without the necessity of interaction via a central point. However, in order for two networks users (ir peers) to communicate, they must have a means to locate and address each other, which is in gernal called a discovery protocol. There are many different solutions for discoverying protocols that work efficiently in fixed or slow-moving networks, but full mobility introduces a set of new difficulties for the discovery of peers and their services. The potential changes in location, which can occur very ofter, the changes in IP address that these changes cuase, and roaming between networks of different kinds are good examples of these difficulties. To solve these problems, a new Service Peer Discovery Protocol was designed and a test application built. The next step towards the introduction of this protocol was creating a working implementation, setting up a suitable test environment, performing experiments, and evaluating its performance. This evaluation could lead to improvments in the protoocl. The aim of this thesis is to implement and document the Service Peer Discovery Protocol, to carry out measurements of it, to evaluate the efficiency of the protocol, and to suggest ways in which it could be improved. The Service Peer Discovery Protocol was found to be well targeted to wireless, peer-to-peer networks, althgouh improvements in the protocol could make it more time and traffic-efficient while maintaining the same level of performance. / Detta är den slutliga rapporten för examensarbetet "Implementation och utvädering av Service Peer Discovery Protocol", utfört på Center for Wireless Systems, KTH, Stockholm.  Uppsatsen behandlar problemet med sökning efter tjänster i icke-hierarkiska (peer-to-peer) mobila nätverk genom att implementera och utvädera ett redan konstruerat protokoll (Service Peer Discovery Protocol). Den huvudsakliga fördelen med icke-hierarkiska nätverk är att anslutna anvndare (parter) kan kommunicera direkt med varandra, utan att behöva interagera med en central punkt.  Dock måste metoder för att lokalisera och adressera andra parter vara tillgängliga för att parterna skall kunna kommunicera, metoder som kalla sökprotokoll (discovery protocol). Det finns många olika sökprotokollösningar som fungerar effektivt i fasta eller långsamma mobila nätverk, men med full mobilitet introduceras ett antal nya svårigheter vid s kande efter parter och tjänster. Den potentiella förändringen av position (vilken kan inträffa ofta), byte av IP-address som dessa förändringar medför, och förflyttning mellan olika typer av nätverk, är exempel på sådana svårigheter. För att lösa dessa problem, konstruerades protokollet Service Peer Discovery Protocol och en testapplikation byggdes.  Nästa steg mot en introducering av detta protokoll var en fungerande implementation, en lämplig testmilö, utförandet av tester och en utvädering av prestandan.  Utväderingen syftade till att förbättra protokollet.  Syftet med detta examensar1ete är att implementera och dokumentera protokollet Service Peer Discovery Protocol, att göra mätningar, att utvädera effektiviteten samt att föreslå förbättringar av protokollet. Service Peer Discovery Protocol, fanns vara väl anpassat till icke-hierarkiska trådlösa nätverk.  Dock torde förbättringar av protokollet innebära tidseffektivare och trafikeffektivare beteende utan att kompromissa prestandanivån.

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While distributed databases offer great promise their decentralized nature poses a number of security and privacy issues. In what ways can parties misbehave? If a database is truly distributed can a malicious actor hide their misdeeds by presenting conflicting views of the database? Can we overcome such deceit and either prevent it by eliminating trust assumptions or detect such perfidy and hold the malicious party to account? We study these questions across two distributed databases: RPKI (Resource Public Key Infrastructure), which is used to authenticate the allocation and announcement of IP prefixes; and Bitcoin, a cryptocurrency that utilizes a permissionless database called a blockchain to track the transfer and ownership of bitcoins. The first part of this dissertation focuses on RPKI and the potential of RPKI authorities to misbehave. We consider the methods, motivations, and impact of this misbehavior and how an RPKI authority can present inconsistent views to hide this misbehavior. After studying the problem we propose solutions to detect and identify such misbehavior. Now we turn our attention to Bitcoin. We look at ways an attacker can manipulate Bitcoin's Peer-to-Peer network to cause members of the network to have inconsistent views of Bitcoin's blockchain and subvert Bitcoin's core security guarantees. We then propose countermeasures to harden Bitcoin against such attacks. The final part of this dissertation discusses the problem of privacy in Bitcoin. Many of the protocols developed to address Bitcoin's privacy limitations introduce trusted parties. We instead design privacy enhancing protocols that use an untrusted intermediary to mix \aka anonymize, bitcoin transactions via blind signatures. To do this we must invent a novel blind signature fair-exchange protocol that runs on Bitcoin's blockchain. This dissertation favors a dirty slate design process. We work to layer protections on existing protocols and when we must make changes to the underlying protocol we carefully weigh compatibility and deployment considerations. This philosophy has resulted in some of the research described in this dissertation influencing the design of deployed protocols. In the case of Bitcoin our research is currently used to harden a network controlling approximately a trillion dollars.

Thesis advisor: Lillie R. Albert / In a world where collaborative learning and social interactions play pivotal roles in educational success, this study explores the dynamics of elementary students’ help-seeking behaviors in mathematics education. Employing Social Network Analysis (SNA), regression models, and comprehensive statistical analyses, the study explores the association between students’ mathematics help-seeking networks and their performance, while also examining the potential moderating effect of socioeconomic status (SES). Furthermore, the study investigates the influence of SES on students’ selection of helpers when facing academic challenges in mathematics. The findings reveal a positive association between students’ mathematics help-seeking indegree centrality—indicative of being nominated as a helper—and their performance. Conversely, a negative association is observed between mathematics help-seeking outdegree centrality—reflective of seeking help from others—and performance. However, these associations were not found to be significantly moderated by SES. Instead, SES influences the choice of helper sources, demonstrating a disparity in access to educational support. Students from wealthier backgrounds tend to rely on outside-of-school resources such as parental support and private tutoring to a greater extent than expected from a random sample, while students from less affluent backgrounds depend more on within-school resources, such as teachers and peers. The study emphasizes the importance of cultivating classroom cultures that value constructive help-seeking, which is integral to enhancing understanding and creating collaborative learning environments. Additionally, the study sheds light on educational inequalities linked to cultural capital, particularly concerning the accessibility of help resources. To address these disparities, strategies such as parental engagement workshops and the development of comprehensive digital platforms are recommended to promote equitable access to assistance across socioeconomic spectrums. Moreover, the potential of Artificial Intelligence in education is noted as a promising tool for providing personalized student support, capable of bridging socioeconomic and cultural gaps. This research concludes with a call to action for educators, policymakers, and community stakeholders to establish educational environments that encourage help-seeking as an effective learning strategy and support equitable access to resources. Such initiatives are crucial for promoting equal opportunities for educational resources and empowering every student to reach their full potential. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Lynch School of Education. / Discipline: Teaching, Curriculum, and Society.

Legal issues of the Internet from the scope of international and national law Global internet network has changed the social, political and business life of most people in the World. Communication is much faster, the flow of information all around the World takes a few seconds. Exchange of political opinions, personal and business information, works protected by copyright and other information has become unstoppable. Members of the international community are trying to tackle this new challenge to their legal and political systems. This diploma thesis is describing some arreas of private law where Internet plays the most important role and has changed the scope and interpretation of many legal rules. The work is dividend into two main parts. The first one deals with general aspects of the Internet such as its history, architecture, different regulatory layers, the copyright law on-line, general legal issues arising from the Yahoo! case and its impact on political systems. The second part describes more specific areas mainly focused on the protection of personality and personal data in the on-line environment. To be more specific, there are chapters dealing with communication software, social networks, direct business and usage of the Internet for business reasons. Specific chapter is dedicated to...