Ethereum is one of the top blockchain platforms that represents this second generation of blockchain technology. However, the security vulnerabilities associated with smart contracts pose significant risks to confidentiality, integrity, and availability of applications supported by Ethereum. While several studies have enumerated various security issues in smart contracts, only a handful have identified the factors that determine the severity and potential of these issues to pose significant risks in practice. As its first contribution, this thesis presents a framework that identifies such factors and highlights the most critical security threats and vulnerabilities of Ethereum smart contracts. To achieve this, we conduct a comprehensive literature review to identify and categorize the vulnerabilities, assess their potential impact, and evaluate the likelihood of exploitation in real-life contracts. We classify the identified vulnerabilities based on their nature and severity and proposed mitigation recommendations. Our theoretical contribution is to establish a correlation between the security vulnerabilities of smart contracts and their potential impact on the security of smart contracts by identifying factors that pose a (practical) threat. Our practical contribution involves developing a tool based on staticanalysis that can automatically detect at least one critical securityissue with the highest threat factor. For the target vulnerability, wechoose the usage of input from external users without any validation.This vulnerability, as we call it, Missing Input Validation (MIV), actsas a root cause for further (well-known and well-researched) issues,for instance, the flow of tainted values into sensitive operations suchas the transfer of cryptocurrencies and self destruct instruction. Weimplement the tool MIV Checker and evaluate its efficacy on a test setof 36 smart contracts. Our evaluation results show that MIV Checkercorrectly detects 87.6 % of instances of MIV in the dataset.

Cryptocurrencies are one of the most prominent applications of blockchain systems. While cryptocurrencies promise many features and advantages, such as decentralization, anonymity, and ease of access, those very features can be abused. For instance, as documented in various recent works, cryptocurrencies have been frequently abused in many different forms of cybercrime. Despite the plethora of works on measuring and understanding the abuse of cryptocurrencies in the digital space, there has been no work on systemizing this knowledge by comprehensively understanding those contributions, contrasting them based on their merit, and understanding the gap in this research space. This thesis initiates the systematic review and understanding of the literature on cryptocurrencies and their utilization in cybercrime. Starting with a rich set of research efforts published exclusively at some of the most highly selective avenues in the cyber security research community, we built a taxonomy of cryptocurrencies, enumerating the most prominent ones based on their use. We then categorize the literature in this space based on the objectives of the tools built and the blockchain systems they target. We then extend our effort by categorizing the reviewed work on cybercrime based on the type of attacks (coordinated vs. individual fraud) and targeted entity (marketplace vs. exchange). Each of those elements in our taxonomy enumerates various aspects of abuse, including their use in underground forums, the trade of drugs, weapons, and stolen credentials, money laundering, malware distribution, ransomware, etc. Accompanying our review, we discuss the gaps in research that call for further investigation.

Titel: Kan funktioner från kryptovalutor förbättra Riksbankens föreslagna E-krona? Författare: Oscar Guregård och Viktor Nilsson Handledare: Mikael Knutsson Bakgrund: I takt med digitaliseringen minskar det fysiska kontantanvändandet. Riksbanken bemöter denna förändring med att utforska möjligheterna att ge ut en digitala kontanter, E-kronan. Eftersom detta är ett nytt område för Riksbanken och projektet fortfarande är i en utvecklingsfas finns det problemområden med de funktioner som Ekronan planeras ha. Forskning inom utveckling av digitala centralbankspengar antyder att kryptovalutor, ett alternativ till centraliserade betalningsstrukturer, har olika funktioner som kan lämpa sig väl för digitala utföranden av valutor. Studien ämnar att analysera olika funktioner inom kryptovalutorna Bitcoin, Ethereum och Ripple för att avgöra om de kan förbättra den föreslagna E-kronan. Syfte: Studiens syfte är att utifrån Riksbankens mål identifiera svagheter och problemområden i det nuvarande förslaget på teknisk lösning för E-kronan för att sedan analysera om funktioner från kryptovalutor kan åtgärda dessa. Om en funktion från en kryptovaluta kan åtgärda ett problem med E-kronan ska det undersökas på vilket sätt funktionen uppfyller Riksbankens mål till en högre grad än den nuvarande lösningen på problemet. Metod: En kvalitativ metod har använts för att samla tidigare forskning om fenomenet digitala centralbankspengar samt Riksbankens egna rapporter om E-kronans utförande för att genom intervjuer med kritiker finna problemområden. Dessa problemområden har med hjälp av funktioner från Bitcoin, Ethereum och Ripple analyserats för att avgöra om kryptovalutornas funktioner är bättre lämpade för att uppfylla E-kronans mål än Riksbankens egna förslag. Resultat: Studien finner att E-kronans största problemområden grundar sig i en överdriven komplexitet. Kryptovalutorna som undersökts och deras funktioner kommer med stor sannolikhet bidra till ännu mer komplexa utföranden istället för att skapa enklare lösningar, något som E-kronans kritiker värdesätter. / Title: Can functions from cryptocurrencies improve the Riksbank’s proposed E-krona? Authors: Oscar Guregård and Viktor Nilsson Supervisor: Mikael Knutsson Background: As digitalisation develops, the use of physical banknotes and cash decreases. The Riksbank is responding to this by exploring the possibility of issuing digital cash, the E-krona. As this is uncharted territory for the Riksbank and the project is still in development, there are challenges with the proposed functions that the E-krona is expected exhibit. Research in the development of Central Bank Digital Currencies, CBDC, suggests that cryptocurrencies, an alternative to centralized payment structures, have a variety of functions that may be well suited for CBDC’s. The study aims to analyze various features and functions of the cryptocurrencies Bitcoin, Ethereum and Ripple in order to determine whether they can improve the proposed E-krona or not. Purpose/object: The aim of the study is to identify weaknesses and problem areas in the current proposal for a technical solution for the E-krona based on the goals and objectives presented by the Riksbank, and to then analyze whether functions from cryptocurrencies can remedy these. If a function from a cryptocurrency can solve a problem with the E-krona, the study must examine in what way the function meets the Riksbank’s objectives to a greater degree than the current proposed solution. Methodology: A qualitative methodology has been used to gather previously researched data on the phenomenon CBDC and the Riksbank’s own reports on the aspects of the E-krona in order to find problem areas through interviews with critics of the project. These problem areas have been analyzed along with functions from Bitcoin, Ethereum and Ripple to determine whether the cryptocurrencies’ functions are better suited to meet the E-krona’s goals than the Riksbank’s own proposals. Results: The study finds that the E-krona’s biggest problem areas are based on excessive complexity. The cryptocurrencies that have been examined and their functions will probably contribute to even greater complexity in the functions of the E-krona instead of creating simpler solutions, something that the critics value.

Electronic voting systems have the potential to offer a cost effective, secure and transparent way of communicating with the citizens, increasing trust and participation. However creating a secure open source electronic voting system providing confidentiality and transparency with sufficient performance has long been a challenge.This thesis proposes a Proof-of-Concept (PoC) for a blockchain-based e-voting system in the absence of government-approved digital ID, aiming to provide a resource for public actors, offering a functional smart contract implementation and suggests an infrastructure design it can utilize. The infrastructure design for the PoC features Hyperledger Besu in a permissioned configuration using PoA (QBFT) algorithm with14 nodes. The voting process involves: account generation and distribution via mail by the government, voter-created passwords encrypting browser generated wallets with voting rights acquired by blind signatures. These components work in conjunction with a smart contract, which serves as the central mechanism for handling the voting process. The thesis finds the system meets the key criterias for an evidence-based e-voting system to a high degree but require testing of the infrastructure design together with the smart contract to assess the performance in order to determine the practical feasibility.

Die Erfindung von Bitcoin hat ein großes Interesse an dezentralen Systemen geweckt. Eine häufige Zuschreibung an dezentrale Systeme ist dabei, dass eine Dezentralisierung automatisch zu einer höheren Sicherheit und Widerstandsfähigkeit gegenüber Angriffen führt. Diese Dissertation widmet sich dieser Zuschreibung, indem untersucht wird, ob dezentralisierte Anwendungen tatsächlich so robust sind. Dafür werden exemplarisch drei Systeme untersucht, die häufig als Komponenten in komplexen Blockchain-Anwendungen benutzt werden: Ethereum als Infrastruktur, IPFS zur verteilten Datenspeicherung und schließlich "Stablecoins" als Tokens mit Wertstabilität. Die Sicherheit und Robustheit dieser einzelnen Komponenten bestimmt maßgeblich die Sicherheit des Gesamtsystems in dem sie verwendet werden; darüber hinaus erlaubt der Fokus auf Komponenten Schlussfolgerungen über individuelle Anwendungen hinaus. Für die entsprechende Analyse bedient sich diese Arbeit einer empirisch motivierten, meist Netzwerklayer-basierten Perspektive -- angereichert mit einer ökonomischen im Kontext von Wertstabilen Tokens. Dieses empirische Verständnis ermöglicht es Aussagen über die inhärenten Eigenschaften der studierten Systeme zu treffen. Ein zentrales Ergebnis dieser Arbeit ist die Entdeckung und Demonstration einer "Eclipse-Attack" auf das Ethereum Overlay. Mittels eines solchen Angriffs kann ein Angreifer die Verbreitung von Transaktionen und Blöcken behindern und Netzwerkteilnehmer aus dem Overlay ausschließen. Des weiteren wird das IPFS-Netzwerk umfassend analysiert und kartografiert mithilfe (1) systematischer Crawls der DHT sowie (2) des Mitschneidens von Anfragenachrichten für Daten. Erkenntlich wird hierbei, dass die hybride Overlay-Struktur von IPFS Segen und Fluch zugleich ist, da das Gesamtsystem zwar robust gegen Angriffe ist, gleichzeitig aber eine umfassende Überwachung der Netzwerkteilnehmer ermöglicht wird. Im Rahmen der wertstabilen Kryptowährungen wird ein Klassifikations-Framework vorgestellt und auf aktuelle Entwicklungen im Gebiet der "Stablecoins" angewandt. Mit diesem Framework wird somit (1) der aktuelle Zustand der Stablecoin-Landschaft sortiert und (2) ein Mittel zur Verfügung gestellt, um auch zukünftige Designs einzuordnen und zu verstehen. / The inception of Bitcoin has sparked a large interest in decentralized systems. In particular, popular narratives imply that decentralization automatically leads to a high security and resilience against attacks, even against powerful adversaries. In this thesis, we investigate whether these ascriptions are appropriate and if decentralized applications are as robust as they are made out to be. To this end, we exemplarily analyze three widely-used systems that function as building blocks for blockchain applications: Ethereum as basic infrastructure, IPFS for distributed storage and lastly "stablecoins" as tokens with a stable value. As reoccurring building blocks for decentralized applications these examples significantly determine the security and resilience of the overall application. Furthermore, focusing on these building blocks allows us to look past individual applications and focus on inherent systemic properties. The analysis is driven by a strong empirical, mostly network-layer based perspective; enriched with an economic point of view in the context of monetary stabilization. The resulting practical understanding allows us to delve into the systems' inherent properties. The fundamental results of this thesis include the demonstration of a network-layer Eclipse attack on the Ethereum overlay which can be leveraged to impede the delivery of transaction and blocks with dire consequences for applications built on top of Ethereum. Furthermore, we extensively map the IPFS network through (1) systematic crawling of its DHT, as well as (2) monitoring content requests. We show that while IPFS' hybrid overlay structure renders it quite robust against attacks, this virtue of the overlay is simultaneously a curse, as it allows for extensive monitoring of participating peers and the data they request. Lastly, we exchange the network-layer perspective for a mostly economic one in the context of monetary stabilization. We present a classification framework to (1) map out the stablecoin landscape and (2) provide means to pigeon-hole future system designs. With our work we not only scrutinize ascriptions attributed to decentral technologies; we also reached out to IPFS and Ethereum developers to discuss results and remedy potential attack vectors.

Currency has changed a lot, and the introduction of the Internet sped up the evolution of the currency. Digital currency introduced many benefits compared to physical currencies. Ideas such as cryptocurrencies work as an option for other means of payment. During the recent pandemic, interest in new digital currencies has increased, leading to more research on digital currency. With the introduction of new currencies and their increased popularity, many central banks have started looking into the idea of innovating currency. All this new research has coined the term central bank digital currency. As of today, there is no single idea on how a digital currency should work or be implemented. With many variations, the future is still unclear. There seem to be vulnerabilities to solve and many potential ways to improve current systems. When building this new currency it is crucial to know what different use cases could demand from the implementation. In conclusion, the results show that digital currency is still in early development, with central bank digital currency research showing promise. It is theoretically possible to create a better transaction solution contra traditional currencies. More research is needed on the topic of digital currency, but there could be incremental improvements to today’s currency leading to better future solutions. / Valuta har förändrats genom tiderna och introductionen av internet skyndade på denna utveckling. Digital valuta har introducerat många fördelar jämfört med fysiska valutor. Fler idéer som till exempel kryptovalutor har introducerats som alternativa betalmedel. Under den senaste pandemin så har intresset för nya digitala valutor ökat, vilket har lett till mer forskning inom området av digitala valutor. På grund av växande popularitet och nya digitala valutor så har många central banker börjat testa idéen om att nyskapa valuta, och med detta så har termen centralbanks valuta skapats. Det finns inte idag en enda lösning på hur digitala valutor ska fungera eller bli implementerade. Med många varianter så är framtiden fortfarande oklar. Det verkar finnas problem att lösa och många möjliga sätt att förbättra existerande system. Vid byggandet av denna nya valuta så är det extremt viktigt att veta vad som är viktigt och hur det kan finnas olika krav beroende på hur valutan ska användas. Enligt resultaten så är digital valuta fortfarande tidigt i sin utveckling och forsking gällande centralbanks styrda digitala valutor verkar lovande. Mer forsking kommer att behövas inom området digital valuta, men det kan komma många små förbättringar på dagens valuta som leder till bättre framtida lösningar.

The purpose of this thesis is to determine the feasibility of using blockchain to implement proof of location. There has been an increasing demand for a way to create a validated proof of location that is economical, and easy to deploy as well as portable. There are several reasons for an increased demand in this technology including the ever-increasing number of mobile gamers that have been able to spoof their location successfully, the increasing number of on demand package shipments from companies such as Amazon, and the desire to reduce the occurrence of medical errors as well as holding hospitals accountable for their errors. Additional reasons that this technology is gaining popularity and increasing in demand is due the continually increasing number of lost baggage claims that airlines are receiving, as well as insurance companies desire to reduce the number of fraud cases that are related to high-value goods as well as increasing the probability of their recovery. Within the past year, there has been an extensive amount of research as well as work that has been completed to create an irrefutable method of location verification, which will permit a user to be able to create time-stamped documentation validating that they were at a particular location at a certain day and time. Additionally, the user is then permitted to release the information at a later date and time that is convenient for them. This research was completed using a Raspberry Pi 3B, a Raspberry Pi 3B+, two virtual Raspberry Pi’s as well as two virtual servers in which the goal was to download, and setup either Ethereum and/or Tendermint Blockchain on each piece of equipment. After completely synchronizing the blockchain it be used to store the verified location data that been time-stamped. There was a variety of issues that were encountered during the setup and installation of the blockchains on the equipment including overclocking processors, which negatively affected the computational abilities of the devices as well as causing overheating and surges in voltage as well as a variety of software and hardware incompatibilities. These issues when looked at individually appear to not have much of an impact on the results of this research but when combined together it is obvious that they reduced the results that could be obtained. In conclusion, the combination of hardware and software issues when combined with the temperature and voltage issues that were due to the overheating of the processor resulted in several insurmountable issues that could not be overcome. There are several recommendations for continuing this work including presyncing the blockchain using a computer, using a device that has more functionality and computational abilities, connecting a cooling device such as a fan or adding a heat sink, increasing the available power supply, utilizing an externally power hard drive for data storage, recreate this research with the goal in mind of determining what process or application was causing the high processor usage, or creating a distributed system that utilizes both physical and virtual equipment to reduce the amount of work on one type of device.

E-tjänster används oftare i Sverige och studier visar att en majoritet av befolkningen vill ha möjlighet att rösta i val via internet. Grannländer som Norge och andra europeiska länder har antingen testat eller implementerat ett e-röstningssystem för demokratiska val, men många av har fått utstå stor kritik eller har lagts ner, som e-röstningsprojektet i Norge. I den här designvetenskapliga studien har vi utvecklat en prototyp av ett e-röstningssystem byggt på smarta kontrakt och blockkedjeteknik med syfte att studera hur väl ett sådant system uppfyller de tekniska kraven som finns för ett svenskt e-röstningssystem. Prototypen utvärderades genom användbarhetstester med potientella slutanvändare samt intervjuer med experter, för att sedan jämföra resultaten med framtagna riktlinjer. Resultatet av denna utvärdering diskuteras sedan där vi tittar på implikationer av ett sådant system tillsammans med fördelar, nackdelar samt potentialen för praktisk realiserbarhet och möjligheter för vidare forskning. Ett e-röstningssystem baserat på smarta kontrakt och blockkedje-teknik är realiserbart inom ramen för denna studie, men framtagandet av verktyg och en högre grad av kryptering är kritisk för ett storskaligt system.

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.

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.