Les systèmes décentralisés sont par nature extensibles mais sont également difficiles à coordonner en raison de leur faible couplage. La réplication de données dans ces systèmes géo-répartis est donc un défi inhérent à leur structure. Les deux contributions de cette thèse exploitent l'hétérogénéité des besoins des utilisateurs et permettent une qualité de service personnalisable pour la réplication de données dans les systèmes décentralisés. Notre première contribution Gossip Primary-Secondary étend le critère de cohérence Update consistency Primary-Secondary afin d'offrir des garanties différenciées de cohérence et de latence de messages pour la réplication de données à grande échelle. Notre seconde contribution Dietcoin enrichit Bitcoin avec des nœuds diet qui peuvent (i) vérifier la validité de sous-chaînes de blocs en évitant le coût exorbitant de la vérification initiale et (ii) choisir leur propres garanties de sécurité et de consommation de ressources. / Decentralized systems are scalable by design but also difficult to coordinate due to their weak coupling. Replicating data in these geo-distributed systems is therefore a challenge inherent to their structure. The two contributions of this thesis exploit the heterogeneity of user requirements and enable personalizable quality of services for data replication in decentralized systems. Our first contribution Gossip Primary-Secondary enables the consistency criterion Update consistency Primary-Secondary to offer differentiated guarantees in terms of consistency and message delivery latency for large-scale data replication. Our second contribution Dietcoin enriches Bitcoin with diet nodes that can (i) verify the correctness of entire subchains of blocks while avoiding the exorbitant cost of bootstrap verification and (ii) personalize their own security and resource consumption guarantees.

This diploma theses concerns the matter of blockchain technology and its practical use, especially for nonfinancial services. Theoretical part describes the blockchain technology from the technological and juridical point of view and examples of its practical use are also mentioned. In the practical part two laboratory exercises were designed for further familiarization of the blockchain technology, in which students try some real applications on their own.

This diploma thesis deals with the creation of a design for the utilization of blockchain technology in a corporate environment. The main goal of this work is to create a proposal for a business process and its implementation in a specific blockchain platform. The analysis of the current state of the process describes current process and company’s requirements for the functionality of new technology. In the design part of the work, I compared specific blockchain platforms. As a result of this part I chose the most suitable solution for the implementation of my proposal. This chapter further includes the design of a methodology for verifying whether the process is suitable for the implementation of a blockchain technology or not. Moreover, it describes how to proceed when choosing a suitable solution and highlights its key factors.

Context - Blockchain-based smart contracts have drawn the attention of scientific communities and businesses in recent years. The development of blockchain-based smart contracts is different from the development of conventional software due to the blockchain characteristics such as immutability, trustlessness, being append-only, and being decentralized. Therefore, standard software engineering processes need to be adjusted to address the unique characteristics of blockchain. Objective - This thesis aims to create a structured map of current research on the development of blockchain-based smart contracts, with a focus on identifying and classifying the development phases. Method - To accomplish our objective, we carried out a systematic mapping study on blockchain-based smart contract development. Our search yielded 1257 potentially related studies that were subjected to a selection process. Subsequently, in the final set appeared 41  primary studies. Result - Our main findings after analysis of the data are as follow:  (i) researches mainly contribute to methods and providing tools, (ii) a  large number of workshop papers indicate smart contracts' high acceptance rate, (iii) there is a lack of research on the finalization as a development phase, (iv) there is no common or standard language for specifying smart contracts that are valid regardless of the blockchain platform, (v)  the most common language paradigm for smart contracts specification is imperative/declarative and for smart contracts implementation is declarative, (vi) the research community has put too much effort into the Ethereum blockchain, while it requires putting more attention to other blockchains, and (vii) there is a lack of studies tackling trustworthy oracle and scam challenges. conclusion - These results can benefit the research community to identify trends, constraints, and research gaps. In addition, they share potential directions for future research.

In this work, we will test the possibility to use Blockchain to preserve data suchas logs. Data inside Blockchain is preserved to be used as digital evidence. Thestudy will examine if Blockchain technology will satisfy the requirement for digitalevidence in a Swedish court. The study will simulate different test scenarios. Eachscenario will be tested on three different hardware configurations. The test has twomain categories, stream test and batch test. In stream test, we test performanceimpact on different systems in case each log is sent in a separate block. While inbatch test, we have two categories batch with data and batch without data. In thistest, we simulate sending 80GB of data each day. In total we send 80GB of data,but the difference here is that we change the time between each block and adjustthe size of the block. In our tests, we focused on three metrics: CPU load, networkbandwidth usage and storage consumption for each scenario. After the tests, wecollected the data and compared the results of each hardware configuration withinthe same scenario. It was concluded that Blockchain does not scale up in streammode, and it is limited to ten blocks/s regardless of hardware configuration. On theother hand, Blockchain can manage 80GB of data each day without stressing systemresources. / Det följande arbetet undersöker vilka möjligheter som Blockchain har som ett verk-tyg för att spara och bevara känslig data, för att kunna användas som digitala be-vis. Dessutom ska studien undersöka giltigheten av Blockchain-tekniken som bevisi domstolen. Studien bygger på ett test som simulerar 15 scenarier med tre olikahårdvarukonfigurationer. Testet delas upp i två huvudkategorier, stream test ochbatch test. I stream testet, testar vi prestationseffekten på olika system när varjelogg skickas i ett separat block. Under batch testet har vi två underkategorier vilkaär batch med data och batch utan data. I batch testet simulerar vi att skicka 80GB data varje dag. Under batch testet har vi dessutom testat att ändra på tidenmellan varje block generering och även justerat blockens storlek. I våra test har vifokuserat på tre mätvärden: CPU-belastning, användning av nätverksbandbredd ochkonsumtion av lagringsutrymmet i varje scenario. När samtliga test slutförts, bör-jade vi med datainsamling och jämförde resultaten från varje system inom sammascenario. Slutsatsen är att Blockchain inte skalar upp i stream testet, då max antalblock som skapas och skickas till data-noder är begränsat till tio block/sek, oavsetthårdvarukonfiguration. Däremot, vid batch testet , kan Blockchain hantera över-föring av 80 GB data varje dag (24 timmar) utan att anstränga systemsresurser.

Voting and general elections serves as a cornerstone of modern democracies as it is through this process that the public makes their political positions heard and collectively elect leaders. While many parts of governments across the world are focusing heavily on digitization, voting is one area that remains offline and analog in many developed countries. Current voting systems continue to be scrutinized, most notably in the US after the 2016 presidential election where integrity of votes was put into question. This calls for innovation in the area of voting and blockchain has proven to be a disruptive technology in other areas to introduce transparency and integrity with an immutable and append-only ledger to store information. While the basic characteristics of blockchain may be desirable for a voting system, there has not yet been an implementation of Blockchain Enabled Voting (BEV). In this thesis, we assess current proposals of BEV in the context of the nine-degree Technology Readiness Level (TRL) scale to get an overview of how mature the technology is in its current state and what needs to be done to reach further maturity. We do this by consolidating necessary requirements to fulfill for a voting system, based on literature review along with guidelines from the National Institute of Standards and Technology (NIST). We follow this up with translating the TRL scale to suit BEV, as the scale was originally designed for technology used by NASA, and then we review design artifacts of BEV in light of this scale. This enables us to make an informed argument about the current state of the technology as well as what is needed to advance the technology for further maturity. Based on the review of current proposals, flight-readiness of BEV in its current state is still immature. Our analysis shows that there are two emerging design principles, complete decentralization, and partial decentralization, where the former is structured similarly to the cryptocurrencies Bitcoin and Ethereum, who considers all nodes as equals and only has governance through engineering. The partially decentralized approach on the other hand is built on permissioned blockchain with some centralized authority and considers the blockchain as a ballot box, or storage of votes. The results show that both design principles are far from flight-ready as they either do not meet the basic requirements of a voting system or make assumptions about the holistic voting systems, especially in areas of establishing voter eligibility, ease of use as well as scalability and robustness. Further research of both approaches is necessary to establish systems that are more defined and are ready for experimental testing.

Sverige är ett av de mest framträdande digitaliserade länderna inom EU. Men vissa sektorer har hamnat efter i digitaliseringsprocessen, en av dem är sjukvården. Sjukvården är en av de mest informationsintensiva sektorerna i det svenska samhället, det är kritiskt att IT-systemen är sammanhållna och kommunicerande med varandra, s.k. interoperabla. Just där brister sjukvårdens IT-system idag, men sjukvården som organisation brister också i att ha någon form av enhetlig standard för hur vårdinformation ska dokumenteras. Dessa brister leder till försämrad vårdkvalitet och arbetsmiljö för vårdpersonalen. Syftet med denna studie är att utveckla en artefakt för hur blockkedjeteknikens egenskaper kan användas för att förbättra interoperabiliteten i de svenska hälso- och sjukvårdssystemen. Vi har genomfört studien med en designbaserad metod, där vi tar fram en modell baserat på blockkedjans egenskaper och presenterade problem utifrån sex intervjuer av personer som arbetar med IT i vården. Vårt resultat visar att blockkedjan har egenskaper som kan stödja interoperabilitet i sjukvården. Resultatet visar också det krävs en balans mellan säkerhet och flexibilitet samt någon form av standard för hur vårdinformation ska dokumenteras, antingen på nationell eller regional nivå, för att skapa interoperabilitet. / Sweden is one of the most prominent digitized countries within the European Union. But some sectors have fallen behind in the digitizing process; one of them is the healthcare sector. The healthcare sector is one of the most information intensive fields in the Swedish society, where it is critical that the IT-systems are integrated and communicative with each other, so-called interoperable. Today's IT systems in healthcare are failing in terms of interoperability, but the healthcare itself as an organisation also fails to have some sort of uniform standard for documenting health data. These deficiencies lead to an impaired quality of care for the patients but also a worsened environment for the healthcare professionals. The purpose of this study is to develop an artefact for how the capabilities of the blockchain technology can be used to improve interoperability within the Swedish healthcare systems. We’ve conducted this paper by using a design-science based method, where we have developed a model based on the capabilities of blockchain technology and issues presented based on interviews with six people working with IT within healthcare. Our findings show that the blockchain technology has capabilities that can support interoperability within the healthcare systems. Our findings also show that to achieve interoperability there is a need to balance security and flexibility as well as some form of unified standard for how healthcare data is to be documented, on either a national or regional level.

Denna studie syftar till att undersöka hur blockchain, den distribuerade ledger-tekniken, kan påverka arbetssättet för digital marknadsföring. Vårt mål är att besvara hur arbetet i digital marknadsföring ser ut idag och vilka egenskaper blockchain har som kan ändra förutsättningarna för arbetssättet inom digital marknadsföring. Genom intervjuer med tio digitala byråer har vi skapat förståelse för deras arbete och deras roll i relation till kunder och konsumenter. Resultatet från intervjuer och litteratur har visat på att de digitala byråernas arbetssätt kan förändras med blockchain genom förändrade kundrelationer och genom ett förändrat förhållande till konsumenterna. Den mest troliga adoptionen av blockchain innefattar adoption av vissa egenskaper från teknologin som kan effektivisera eller automatisera arbetet, samt ändra förutsättningarna för arbetet inom digital marknadsföring. Den stora utmaningen för adoptionen är arbetet med att flytta över tillgångar till nätverket och integrera alla användare, som både tar tid och omfattar stora kostnader. Distributionen och krypteringen av information i en blockchain skapar möjligheter för transparens, säkerhet och integritet, men ingen kan säkert veta om blockchain kommer att bli lönsamt. / This study aims to investigate how blockchain, the distributed ledger-technology, can affect the way that digital marketing operates. Our goal is to understand how the work-process in digital marketing functions today, and what characteristics blockchain has that can change the prerequisites for the digital marketing process. Through interviews with ten digital agencies, we have created an understanding of their work and their relationships with customers and consumers. The results from the interviews and literature have shown that the work of digital agencies can change the relationship with customers and consumers through blockchain. The most likely adoption of blockchain includes adoption of certain features from the technology that can streamline or automatize work, as well as change the conditions for the work in digital marketing. The major challenge for the adoption is the overall effort to move over assets to the blockchain network and integrate all users, which both takes time and includes huge costs. The distribution and encryption of information in a blockchain creates opportunities for transparency, security and integrity, but nobody knows for certain if blockchain will be profitable.

During recent years, attacks on Internet of Things (IoT) devices have grown significantly. Cyber criminals have been using compromised IoT machines to attack others, which include critical internet infrastructure systems. Latest attacks increase the urgency for the information security research community to develop new strategies and tools to safeguard vulnerable devices at any level. Millions of intelligent things are now part of home-based networks that are usually disregarded by solutions platforms, but not by malicious entities.<br>Therefore, the following document presents a comprehensive framework that aims to secure home-based networks, but also corporate and service provider ones. The proposed solution utilizes first-hand information from different actors from different levels to create a decentralized privacy-aware Cyber Threat Information (CTI) sharing network, capable of automate network responses by relying on the secure properties of the blockchain powered by the Ethereum algorithms.

Blockchain, a solution for different parties to reach consensus in a peer­to­peer (P2P) networks, allows us to distribute data across different entities. Many areas, including financial, health care, eCommerce, marketing, can benefit from blockchain technology. Influencer marketing also takes benefit from the properties of blockchain technology. Most of the time, social media influencers have an” ideal” body, affecting how theproduct they are advertising looks on them, which results in increased returns inonline shopping. Moreover, existing applications are not involving micro­influencers(10,000 ­ 100,000 followers) in the campaigns that brands have created. In order to tackle the mentioned problems, a blockchain distributed size and fit application framework is proposed in this thesis. The framework offers a possibility for micro influencers to participate in the brands’ campaigns. However, micro­influencers are not directly involved in communication with brands. Instead, macro­influencers (over100,000 followers) play a role as a bridge between micro­influencers and brands by creating sub­campaigns of the brands’ campaigns. With the involvement of micro influencers in the proposed framework, they also share their pictures with the same outfit (different body sizes and shapes), which gives potential buyers a better idea of how the same outfit would look on them before they decide to buy. The proposed solution is implemented with smart contracts using Solidity and tested in the Ropstentest network. Testing the smart contract in the Ropsten test network shows that the proposed solution is feasible in terms of financial costs. The proposed framework is not limited to giving the possibility to only brands to advertise products, but it also offers macro­influencers and potential micro­influencers an opportunity to earna reward in exchange for promoting the products of brands. The whole process starting from applying for a campaign to claiming reward is handled without manual intervention. / Blockchain, en lösning för olika parter för att nå konsensus i ett peer­to­peer­nätverk(P2P), låter oss distribuera data över olika enheter. Många områden, inklusiveekonomi, hälsovård, e­handel, marknadsföring, kan dra nytta av blockchain­teknik.Influencer­marknadsföring drar också nytta av blockchain­teknikens egenskaper.För det mesta har påverkare på sociala medier en ”idealisk” kropp som påverkarhur produkten de annonserar ser ut på dem, vilket resulterar i ökad avkastning ionline­shopping. Dessutom involverar befintliga applikationer inte mikroinfluencer(10 000 ­ 100 000 följare) i de kampanjer som varumärken har skapat. För atthantera de nämnda problemen föreslås en blockchain­distribuerad applikationsrami denna avhandling. Ramverket erbjuder en möjlighet för mikroinfluencer attdelta i varumärkets kampanjer. Mikroinfluencer är dock inte direkt inblandade ikommunikation med varumärken. Istället spelar makroinfluencer (över 100 000följare) en roll som en bro mellan mikroinfluencer och varumärken genom att skapaunderkampanjer av varumärkets kampanjer. Med deltagande av mikroinfluenceri det föreslagna ramverket delar de också sina bilder med samma outfit (olikakroppsstorlekar och former), vilket ger potentiella köpare en bättre uppfattning omhur samma outfit skulle se ut på dem innan de bestämmer sig för att köpa . Denföreslagna lösningen implementeras med smarta kontrakt använder Solidity och testasi Ropsten­testnätverket. Att testa det smarta kontraktet i Ropsten­testnätverket visaratt den föreslagna lösningen är genomförbar när det gäller finansiella kostnader.Den föreslagna ramen är inte begränsad till att ge endast varumärken möjlighetatt marknadsföra produkter, men den ger också makroinflytande och potentiellamikroinfluencer möjlighet att tjäna en belöning i utbyte för att marknadsföraprodukter från varumärken. Hela processen från att ansöka om en kampanj till attfå belöning hanteras utan manuellt ingripande