Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-30T15:34:00Z No. of bitstreams: 1 helderluizpalmiericaldas.pdf: 3093758 bytes, checksum: 78e635406e0664df0546fe72eee1988d (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-30T15:37:48Z (GMT) No. of bitstreams: 1 helderluizpalmiericaldas.pdf: 3093758 bytes, checksum: 78e635406e0664df0546fe72eee1988d (MD5) / Made available in DSpace on 2017-05-30T15:37:48Z (GMT). No. of bitstreams: 1 helderluizpalmiericaldas.pdf: 3093758 bytes, checksum: 78e635406e0664df0546fe72eee1988d (MD5) Previous issue date: 2016-03-07 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O Bitcoin é um sistema de pagamento totalmente digital independente de uma entidade centralizadora como bancos ou governos. O projeto foi criado e publicado em 2008 através da Internet. Entretanto apenas em 2009 a rede tornou-se operacional. O Bitcoin é um protocolo de código aberto e uma rede ponto a ponto de participantes que é responsável pelo funcionamento do sistema. Segurança criptográfica, ausência de taxas e de custos de instalação são fatores que convenceram várias empresas do mundo a adotá-lo como alternativa de pagamento. Apesar dos trabalhos acerca da moeda digital, pouco ainda se sabe sobre sua topologia e características, principalmente pela ótica de ciência de redes. Nesse sentido, o presente trabalho apresenta o estudo da dinamicidade de suas principais variáveis no seu funcionamento diário. No decorrer do trabalho são apresentadas duas formas de extração de dados da rede Bitcoin para futuras análises. / Bitcoin is a fully digital payment system independent of a centralized entity like banks or governments. The Bitcoin project was created and published in 2008. In 2009 the Bitcoin P2P network became operational. The Bitcoin is an open source protocol and a peer-topeer network of participants that is responsible for operating the system. Cryptographic security, absence of exogenous rates and of installation costs convinced several companies in the world to adopt it as a payment alternative. Although, there is an increasing amount of work on digital currencies, little is known about Bitcoin its topology and characteristics, particularly from the viewpoint of network science. In this sense, this paper presents the study of the dynamics of its main variables and their daily functioning. During the work we present two forms of network data extraction Bitcoin for further analysis.

Financial journals have just begun to examine the implications of unsecured fixed-rate loans between lenders and borrowers administered over the internet. This study observes 31,550 loans issued between June 2007 and April 2013 with a 36-month term, that are fully paid or charged off, based on a data set from the largest P2P lending website. Initial findings within peer-to-peer (P2P) lending markets have identified that social disclosures may influence these markets. The result of this analysis unambiguously confirms social disclosures influence lenders and the factors significant for funding a loan are inconsistent with the factors significant to repayment of the loan. Prescriptive filters based on social disclosures can improve the likelihood of selecting a creditworthy borrower and increase the models explanatory power. The study finds that distinct forms of social disclosure and specific content within social disclosures predict the amount of funding received and probability of loan repayment.

As the development of context aware applications has evolved, there has been a corresponding increase in need for more sophisticated system. The aim for this thesis is the development of a dynamical P2P network system which is based on locations. The P2P network is self organizing and in a lightweight format. Modern technical solutions including   AGPS have facilitated the work associated with the ability to position users and modern mathematical solutions such as spherical trigonometry provides the P2P system with the necessary accuracy even for short distances. The P2P system works on different Java platforms including JSE, JME and Android. Unfortunately the 3G network distributor has not yet solved a NAT traversal problem, which means that the P2P network self organization and architecture has only been proved by means of simulations. Another problem is that certain mathematical formulas are required for the spherical trigonometry and the limitation for JME is that it is unable to handle inverse trigonometry. However, the Android and JSE versions can form a correct P2P network, under the condition that the Android device uses a WIFI connection point outside the 3G distributor network system. This thesis reports the successful testing of the locations-based P2P network. / MediaSense

Fully distributed systems offer the highest level of freedom for the users. For this reason, in today’s Internet, it is recorded that more than 50% of the packets moving in and out belong to this type of network. Huge networks of this kind are built on the top of DHTs, which follow a more structured communication compared to the other small peer-to-peer networks. Although nature always favors freedom and independ-ence, security issues force consumers to set up their network in a cen-trally controlled manner. One of security threats posed on such net-works is lookup attacks. A lookup attacks are kind of attacks which targets on disrupting the healthy routing process of the DHTs. Even though the freedom of peer-to-peer networks comes at the cost of securi-ty, it is quite attainable to make the network more secure, especially, it is quite achievable to gain performance on this level of attack according to the experiments carried out in this thesis. The secure routing techniques introduced have been found to outperform those without the techniques under investigation. The simulation performed for default Chord overly and the modified Chord, yielded interesting results, for dropper nodes, random lookup routs and colluding sub-ring attacks.

Peer-to-peer (P2P) applications have become a popular method for obtaining digital content. Recent research has shown that the amount of time spent downloading from a poor performing peer effects the total download duration. Current peer selection strategies attempt to limit the amount of time spent downloading from a poor performing peer, but they do not use both advanced knowledge and service capacity after the connection has been made to aid in peer selection. Advanced knowledge has traditionally been obtained from methods that add additional overhead to the P2P network, such as polling peers for service capacity information, using round trip time techniques to calculate the distance between peers, and by using tracker peers. This work investigated the creation of a new download strategy that replaced the random selection of peers with a method that selects server peers based on historic service capacity and ISP in order to further reduce the amount of time needed to complete a download session. Peer-to-peer (P2P) applications have become a popular method for obtaining digital content. Recent research has shown that the amount of time spent downloading from a poor performing peer effects the total download duration. Current peer selection strategies attempt to limit the amount of time spent downloading from a poor performing peer, but they do not use both advanced knowledge and service capacity after the connection has been made to aid in peer selection. Advanced knowledge has traditionally been obtained from methods that add additional overhead to the P2P network, such as polling peers for service capacity information, using round trip time techniques to calculate the distance between peers, and by using tracker peers. This work investigated the creation of a new download strategy that replaced the random selection of peers with a method that selects server peers based on historic service capacity and ISP in order to further reduce the amount of time needed to complete a download session. The results of this new historic based peer selection strategy have shown that there are benefits in using advanced knowledge to select peers and only replacing the worst performing peers. This new approach showed an average download duration improvement of 16.6% in the single client simulation and an average cross ISP traffic reduction of 55.17% when ISPs were participating in cross ISP throttling. In the multiple clients simulation the new approach showed an average download duration improvement of 53.31% and an average cross ISP traffic reduction of 88.83% when ISPs were participating in cross ISP throttling. This new approach also significantly improved the consistency of the download duration between download sessions allowing for the more accurate prediction of download times.

This thesis is mapping in a detail and describes the current situation and prediction of the penetration of information technology based mostly on the cloud and blockchain technologies into the real global economy and identifying trends that affect these areas. Focus is primarily on socialization of services, concept of sharing economy and financial-technology (FinTech) companies. Next part describes the process of maturing of information technologies, which enables bypassing of costly intermediaries, who are replaced by other users or advanced algorithms in the fields, which werent fundamentally touched by ICT until now. Work intersects the knowledge of the of the IT industry and minor specialization from FFU VSE.

Predmetom diplomovej práce je skúmanie možností realizácie univerzálneho meracieho zariadenia v sieti LTE. Sú popísané základy M2M komunikácie a trendy v IoT. Cieľom práce je nájsť optimálny hardvérový základ, na ktorom následne bude možné konfigurovať LTE modem a získať údaje o stave a kvalite pripojenia k sieti. Následne bude vykonaná séria testov za účelom zmerania parametrov siete a výsledky budú spracované k prezentácii na webovom serveri vo forme grafov.

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

The increasingly adapted technology called blockchain can be viewed as a distributed append-only time-stamped data structure which is made possible by a distributed peer-to-peer network. The network uses cryptography and different consensus mechanisms to ensure immutability, security, transparency, and speed in a decentralized fashion. A permissionless decentralized autonomous organization (DAO) is an application deployed on a blockchain that enables people to govern and coordinate themselves in a decentralized manner through self-executing rules where anyone can join. A foundational function of a DAO is the voting system which dictates how the governance of the DAO is conducted. Voting systems in DAOs are currently not well researched and the currently used solutions have flaws, they are either not secure or they have the risk of resulting in unfair outcomes. This is the problem that this project focuses on. The problem was approached by conducting research in the field and through the conclusions of the research a new solution for a voting system was proposed and implemented. The proposed solution can be used to gain inspiration in further studies or be tested and developed to evaluate it in practice.

The ever increasing demand for video content directed the focus of researchfrom traditional server-based schemes to peer-to-peer systems for videodelivery. In such systems, video data is delivered to the users by utilizing theresources of the users themselves, leading to a potentially scalable solution.Users connect to each other, forming a p2p overlay network on top of theInternet and exchange the video segments among themselves. The performanceof a p2p system is characterized by its capability to deliver the videocontent to all peers without errors and with the smallest possible delay. Thisconstitutes a challenge since peers dynamically join and leave the overlay andalso contribute different amounts of resources to the system.The contribution of this thesis lies in two areas. The first area is theperformance evaluation of the most prominent p2p streaming architectures.We study the streaming quality in multiple-tree-based systems. We derivemodels to evaluate the stability of a multiple tree overlay in dynamic scenariosand the efficiency of the data distribution over the multiple trees. Then, westudy the data propagation in mesh-based overlays. We develop a generalframework for the evaluation of forwarding algorithms in such overlays anduse this framework to evaluate the performance of four different algorithms.The second area of the thesis is a study of streaming in heterogeneous p2poverlays. The streaming quality depends on the aggregate resources that peerscontribute to the system: low average contribution leads to low streamingquality. Therefore, maintaining high streaming quality requires mechanismsthat either prohibit non-contributing peers or encourage contribution. In thisthesis we investigate both approaches. For the former, we derive a model tocapture the evolution of available capacity in an overlay and propose simpleadmission control mechanisms to avoid capacity drainage. For the latter, inour last work, we propose a novel incentive mechanism that maximizes thestreaming quality in an overlay by encouraging highly contributing peers tooffer more of their resources. / QC 20100506