The decentralized and pseudonymous nature of cryptocurrencies like Bitcoin has made it easier for criminal entities to engage in illicit activities online compared to relying on traditional currency systems. Detecting these activities is vital to preventing and combating such abuse. We employ a data collection tool based on a Depth First Search algorithm to follow the largest receivers from 10 illicit starting addresses in each abuse type; Darknet, Blackmail, Tumbler, and Ransomware. The results from our two searches showed that money tends to be concentrated to one or two receivers and that all abuse types rely heavily on so-called Two-Transaction addresses. These addresses are only used once, likely as intermediaries to obfuscate money flow, potentially within the inner layer of Bitcoin Tumblers. The results also showed behaviors within the abuse types that were both consistent with and divergent from existing research. Furthermore, similarities and unique behaviors across the abuse types were identified. Expanding the dataset with deeper searches could yield clearer patterns in money flow behavior. Additionally, increasing the number of data collection points could enhance the analysis. Finally, the starting addresses significantly impacted the trustworthiness and reliability of our results. We hope our findings, lessons, and developed tools will aid future research and the development of strategies to combat online abuse.

Created in 2009, the digital currency of bitcoin is a relatively new phenomenon. During this short period of time, it has however displayed a strong development of both price and trade volume. This has led to increased media attention, but also regulators and researchers have developed an interest. At this moment, the amount of available research is however limited. With a focus on the price volatility of bitcoin and an aim of finding drivers of this volatility, this study is taking a unique position. The research has its basis in the philosophical position of positivism and objectivism. This has shaped the research question as well as the construction of the study. The result is a describing and explaining research with a deductive research approach, a quantitative research method and an archival research strategy. This has in turn stimulated an extensive literature review and information search. Areas of discussion are microstructure theory, the efficient market hypothesis, behavioural finance and informational structures. Due to the limited amount of previous bitcoin research within the area of price volatility, the study has drawn extensively on research performed on more classical assets such as stocks. Nevertheless, when available, bitcoin research has been used as a foundation/reference and an inspiration. Reviews of academic literature and economic theories, as well as public news helped to identify the variables for the empirical study. These variables are; information demand, trade volume, world market index, trend and six specified events, occurring during the chosen sample period and included in the study as dummy variables. The variables are all analysed and included in a GARCH (1,1) model, modified following a similar research by Vlastakis & Markellos (2012) on stocks. This GARCH (1,1) model is then fitted to the bitcoin volatility registered for the sample period and is able thereby able to generate data of if and how the variables affect the bitcoin volatility. The test result suggests that five of the ten variables are significant on a 5 %-level. More specifically it suggests that information demand is a significant variable with a positive influence on the bitcoin volatility, something that corresponds to the literature on information demand and price volatility. This also relates to the events found significant, as they generated bitcoin related information. The significant events of the Cypriot crisis and the failure of the bitcoin exchange MtGox are thus specific examples of how information affects price volatility. Another significant variable is trade volume, which also displays a positive influence on the volatility. The last significant variable turned out to be a constructed positive trend, suggesting that increasing acceptance of bitcoin decreases its volatility.

In this thesis, an analysis of Bitcoin, Monero price and volatility is conducted with respect to S&P500 and the VIX index. Moreover using Python, we computed correlation coefficients of nine cryptocurrencies with two different approaches: Pearson and Spearman from July 2016 -July 2018. Moreover the Pearson correlation coefficient was computed for each year from July2016 - July 2017 - July 2018. It has been concluded that in 2016 the correlation between the selected cryptocurrencies was very weak - almost none, but in 2017 the correlation increased and became moderate positive. In 2018, almost all of the cryptocurrencies were highly correlated. For example, from January until July of 2018, the Bitcoin - Monero correlation was 0.86 and Bitcoin - Ethereum was 0.82.

This master thesis explores how blockchain technologies can be utilized within the financial sector with focus on how to store both private and public information on the blockchain. The capital market is looking into ways of cutting down administrative work through streamlining the financial process by using blockchain technologies. Public key encryption together with hash functions and a consensus mechanism make up the basis for creating a shared trustless database system. The thesis was conducted by extensive research concerning cryptographic topics, and a literature study was made to compare existing solutions. This was done in order to come up with a new design which suggests how to utilize blockchain technologies in order to create private transactions. The design solves issues regarding key management and how to handle both private and public information on the blockchain. The proposed design is an extension of Visigon's existing permissioned blockchain, and it introduces different roles within the peer to peer network as well as a concept of having regulating nodes that together with the involved bank's nodes handle the process of private transactions. Private transactions are encrypted by using symmetric keys and thereafter recorded on the blockchain. In conclusion blockchain technology might not be the most suitable database system for banks to keep transactions private. Future solutions should consider the best attributes of blockchain technologies and create a new system with the single purpose of being a tool for the financial market.

Cette thèse est consacrée à l'étude de la formation des prix sur les marchés financiers, en particulier lorsque ceux-ci se composent d'un grand nombre d'agents. On commence par l'étude empirique d'un marché émergent -- le bitcoin -- de manière à mieux comprendre comment les actions individuelles affectent les prix -- ce que l'on appelle « l'impact de marché ». On développe ensuite un modèle théorique d'impact basé sur le concept d'agent hétérogène, qui parvient à reproduire les observations empiriques d'un impact concave dans un marché non manipulable. Le cadre de l'agent hétérogène nous permet de revisiter les concepts d'offre et de demande dans un cadre dynamique, de mieux comprendre l'impact du mécanisme de marché sur la liquidité, ou encore de poser les bases d'un simulateur de marché réaliste. On montre enfin, à travers l'étude empirique de plusieurs bulles et crashs sur le marché du bitcoin, le rôle crucial de la micro-structure dans la compréhension des phénomènes extrêmes. / This thesis is devoted to the study of price formation on financial markets, in particular when these are composed of a large number of agents. We start by the empirical study of an emergent market -- the bitcoin -- in order to better understand how individual actions impact prices -- a phenomenon known as « market impact ». We then develop a theoretical model based on the concept of heterogeneous agents, that allows to reproduce the empirical observations of a concave impact in a market that remains non-manipulable. The heterogeneous agents framework allows us to revisit the concepts of supply and demand in a dynamic context, to better understand how the choice of a particular market mechanism can impact liquidity, and to lay some grounds for a realistic market simulator. By studying several bubbles and crashes that happened on the bitcoin market, we finally show how relevant microstructure effects can be, in particular for understanding the occurrence of extreme phenomena.

This thesis describes important existing cryptocurrencies and their basis principles. Especially it describes differences between this cryptocurrencies and theid basis principles. Also describes posibilites for analysis of Bitcoin blockchain. Next part describes improvments of tool for blockchain analysis. Futher it describes cryptocurrency analyzing tool, and it's implemented extensions.

This work deals with performance and security testing of blockchain protocols based on the Proof-of-Stake (PoS) consensus model. It describes properties, problems, but also the use of blockchain systems. On theoretical levels, this thesis compares the properties and resistance to various attacks of numerous PoS protocols, specifically Algorand, Casper, Gasper, Snow White, Stellar and Decred. Additionally, this work implements a protocol simulator of Algorand, Casper FFG and Gasper. The simulator is built on top of the Bitcoin Simulator simulation tool, which is based on the NS-3 discrete network event simulator. Then, it compares the properties of the implemented protocols using discrete simulation.

Under början av 2010-talet populariserades en ny form av elektroniskt betalningsmedel, så kallade kryptovalutor. Dessa tillkom under slutet av 2000-talet, till stor del på grund av stora finanskrisen 2007, och fungerar som ett fristående valuta- och betalningssystem. Den första och mest välkända av dessa idag är bitcoin. Bitcoin, som många andra kryptovalutor men ingen i samma grad, genomgick en chockprishöjning under mitten 2010-talet ända fram tills 2018. Priset hade under denna tid rört sig från under $10 USD till över $20000 USD per bitcoin. En sådan ofantlig ökning av pris har skapat ett stort intresse hos många, från hobbyinvesterare till finanssektorns huvudanalytiker. En annan viktig händelse i bitcoins historia är åtalet mot Ross Ulbricht, som skapade en illegal digital handelsplats vid namn Silk Road som accepterade bitcoin. Då det fortfarande är ett nytt område har forskning kring fenomenet inte lämnat krubban än. Dock görs det uppenbart genom en snabb överblick att denna forskning främst ligger inom den ekonomiska sfären. Endast ett fåtal vetenskapliga artiklar som nämner den sociala kopplingen till bitcoin kan återfinnas, särskilt få med en kvalitativ forskningsansats. Det har därför gjort oss intresserade att göra ett tillägg till detta mer eller mindre outforskade fenomen. För att åstadkomma detta har vi valt att fokusera oss på en jämförelse av nyhetsartiklar skrivna från perspektivet av bitcoinvärlden med några av de största internationella mediepublikationer som har skrivit om bitcoin. Norman Faircloughs kritiska diskursanalys ligger till grund för teorin och metoden bakom denna analys. Det är genom hans forskningsansats som en textanalys av fenomenet möjliggörs. Detta ledde till att vi kunde urskilja ett antal olika diskurser från texterna, antagonistiska förhållanden mellan de och dess textuella konstruktion. Utifrån detta har vi härlett till vad vi tolkar vara en möjlig framkomst till sättet nyhetssidorna skriver om bitcoin.

The subject of the thesis is the parallel digital economy created around the monetary innovation called Bitcoin and the interaction between this technology and its users. Bitcoin is a new kind of digital money and a payment system. Transactions are cryptographically verified by users and subsequently recorded in a publicly distributed account book called blockchain. Bitcoin, as an open-source project, has created a worldwide community of Internet-connected users who are further transforming this cryptocurrency by their specific use. Ethnographic research took place during the meetings of the community surrounding the Prague place called Parallel Polis in the period of years 2017-2018 and was subsequently extended to the "online" world. Bitcoin forms the intersection between technology and the economy, and therefore emphasis is placed on exploring the dynamics that this complex phenomenon creates. The work examines the social practices that actors are constantly shaping on the basis of their various motivations through their participation in Bitcoin and the complex ideas connected with it. It examines the visions, attitudes and practices of the "bitcoiners", who support the functioning of this system and allows its very own existence. These ideas are characterized by certain paradoxes and dilemmas...

Titel: Kan Bitcoin bli framtidens betalningsmedel i utvecklingsländer? Författare: Isak Bengtsson och Gustaf Starbrant Bakgrund och problemdiskussion: I utvecklingsländer finns det betydande grupper människor som inte har tillgång till ett fungerande bankkonto. Detta skapar problem i form av finansiellt utanförskap för vissa befolkningsgrupper. Bitcoin är en digital valuta som alla människor i teorin skulle kunna få tillgång till, med en mobiltelefon med nätverksuppkoppling som enda krav. Därigenom skulle fler människor i utvecklingsländer ha tillgång till fungerande betalningsmöjligheter och inte utsättas för finansiellt utanförskap. Forskningsfråga: Vilka möjligheter samt risker finns avseende att införa Bitcoin som betalningsmedel i utvecklingsländer? Syfte: Syftet med studien är att undersöka och analysera möjligheter samt risker avseende införandet av Bitcoin som betalningsmedel i utvecklingsländer. Metod: Genom en abduktiv ansats och en kvalitativ metodik har vi sammanfattat resonemang, argument och forskning kring Bitcoin. Material har samlats in genom tidigare forskning och semistrukturerade intervjuer. Referensram: Bitcoin och blockkedjetekniken presenteras men även Bitcoin som valuta och dess möjligheter och risker. Teorierna förtroendeteori och penningteori belyses också. Dessa utgör grundstenar och används som ett analysverktyg i uppsatsen. Empiri: Vårt empiriska undersökningsområde innefattar personer med kunskap om Bitcoin och dess underliggande teknik, blockkedjetekniken. Insamlandet av det empiriska materialet skedde genom sex semistrukturerade intervjuer. Analys och slutsatser: Bitcoin är den största digitala valutan i dagsläget och erbjuder stora möjligheter generellt. Det finns dock begränsningar, till exempel skalningsproblematik och deflation, som hade gjort det svårt för en implementering som valuta i utvecklingsländer. Däremot innehar blockkedjetekniken stor potential att förändra infrastrukturen för betalningar. Nyckelord: Betalningsmedel, Bitcoin, blockkedjetekniken, digital valuta, möjligheter, risker, utvecklingsländer