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Although cryptography based remote voting protocols have been researched since 1981, most of the previous protocols [9], [5], [13] assume the existence of public bul- letins or, in other words, a publicly readable, tamper-proof, append-only log. As blockchain or distributed ledger technology (DLT) offers properties like irreversibil- ity, transparency and decentralization, it is suitable for realization of public bulletin board for the voting system. We see a gap in the research of blockchain based voting systems because there either exists work on just the protocol aspect of the voting system or the performance aspect of the blockchain. As blockchain is a general purpose tool, we believe that there lies opportunities for micro-optimizations that could specifically benefit the voting system. This ushered us to focus our effort on the performance aspect of integration of voting protocol with blockchain. Hence, in this thesis, we first introduce a homomorphic encryption based voting protocol that uses blockchain, Hyperledger Fabric (HLF), as bulletin board. The protocol is de- signed such that it leverages the transaction processing characteristics of underlying DLT. We then created an experiment where we designed a smart contract, set up a blockchain network and exposed the system to 40k concurrent voting transactions to profile the code of HLF. From the profile data, it was found that execution of cryptographic operations constitutes most of the transaction processing time. This led us to benchmark cryptographic libraries for SHA256 and digital signature algo- rithm and integrate the faster library into HLF for better performance. We also found that the transaction manager of HLF does not need read-write locks to ensure transaction isolation in special scenarios, which alleviates the performance drop due to lock contention. Altogether we were able to improve the throughput and latency of the baseline system by more than 30%. Lastly, we make a comparison between public and permissioned DLT based remote voting system and discuss the suitability of permissioned blockchain for the application of voting systems. / Graduate

Consensus protocols are the core of modern blockchain systems, such as the Bitcoin, Ethereum, and Algorand networks. Thanks to these protocols, participants in a blockchain network can reach consensus on which blocks to add to a blockchain, to have a consistent chain of blocks in the whole network. Blocks are typically collections of transactions, e.g., transferring currency between participants, but can contain other data depending on the use case. Consensus protocols are difficult to design, test, and implement. Problems may only manifest in rare cases but can have disastrous consequences. Formal protocol models allow exhaustive analysis and formal verification. However, formal verification is only as good as the specification of the protocol. For example, specification properties could be vacuously true, or the specification may omit to mention liveness properties that are crucial for progress in a system implementation. This thesis describes the practical validation of a formal specification of Giskard, a consensus protocol used in the PlatON network. We translated key aspects of a formal model of Giskard in the Coq proof assistant to executable Python code, and integrated them into the Sawtooth blockchain framework. Then, we ran simulations of a blockchain network executing Giskard using Sawtooth, checking network node state properties of Giskard as well as its global safety properties. Automated clients from the Sawtooth network provided randomly generated transactions as input for the network. The implementation with the test results are available for reproducibility. Both consensus safety and liveness issues were found in the formal specification of Giskard during the simulations. Based on the previous informal English specification of Giskard, we propose a new formal specification which was validated to reach consensus on blocks in the simulated blockchain network and uphold the protocol’s crash and Byzantine failure tolerance to a certain degree. The improved formal model can serve as a new basis for verifying and implementing Giskard in the future. / Konsensusprotokoll utgör kärnan i moderna blockkedjesystem som Bitcoin-, Ethereum- och Algorandnätverken. Tack vare dessa protokoll kan deltagare i blockkedjenätverk nå konsensus om vilka block som ska läggas till, för att få en konsekvent blockkedja i hela nätverket. Block är vanligen samlingar av transaktioner, till exempel överföringar av valuta mellan deltagare, men kan också innehålla annan data beroende på användningsområdet. Konsensusprotokoll är svåra att designa, testa och implementera. Problem kanske bara visar sig i sällsynta fall, men kan ha katastrofala konsekvenser. Formella protokollmodeller tillåter uttömmande analys och formell verifiering. Men formell verifiering ger bara så goda resultat som protokollspecifikationen tillåter. Till exempel kan specfikationsegenskaper vara sanna innehållslöst eller så kan specifikationen underlåta att nämna framstegsegenskaper som är viktiga för att en systemimplementation inte ska låsa sig. Denna avhandling beskriver den praktiska valideringen av en formell specifikation av Giskard, ett konsensusprotokoll som används i PlatONnätverket. Vi översatte nyckelaspekter av en formell modell i bevisassistenten Coq till körbar Python-kod och integrerade koden i blockkedjeramverket Sawtooth. Sedan körde vi simuleringar av ett blockkedjenätverk som använder Giskard med hjälp av Sawtooth och undersökte Giskards tillståndsegenskaper för nätverksnoder och även dess globala säkerhetsegenskaper. Automatiserade klienter från Sawtooth-nätverket tillhandhöll slumpgenererade transaktioner som indata för nätverket. Implementeringen med testresultaten är tillgängliga för reproducerbarhet. Både säkerhets- och framstegsproblem hittades i den formella specifikationen av Giskard under simuleringarna. Baserat på en tidigare informell specifikation av Giskard på engelska föreslår vi en ny formell specifikation som validerades att nå konsensus på block i det simulerade blockkedjenätverket och att till en viss grad tolerera krascher och byzantinska fel. Den förbättrade formella modellen kan användas som en ny bas för att verifiera och implementera Giskard i framtiden.

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.

This thesis presents an extension to Hyperledger Fabric, a private blockchain system, allowing historic transactions to be pruned without peer coordination. The feature is facilitated via pruning predicate functions, provided along any smart contracts a given system is desired to host. An evaluation of the extension demonstrates its impact, in terms of memory saved, for a specific asset delivery use case. It is concluded that the gains of pruning historic transactions from blockchain systems could yield significantly reduced storage requirements for some categories of applications, especially such with low transaction interdependency. It is also suggested that the deterministic consensus algorithms used by Hyperledger Fabric makes the transaction histories it may maintain not strictly required, meaning that the particular set of transactions that must survive pruning depend on what properties a blockchain is expected to maintain.

As the threat of supply-chain attacks grows, the need for techniques to protect software integrity likewise increases. The concept of reproducible builds is one such protection. By ensuring that a package can be rebuilt in the exact same way every time, reproducible builds allow users to notice when a package has changed even though its source code stays the same. Thus, the knowledge of which packages are reproducible and therefore easier to trust is a crucial part of this protection mechanism. Current strategies for validating and distributing this information rely on the work of a small number of individual entities with limited coordination in-between them, leading to user confusion because of the lack of a central authority. This work describes a protocol for decentralized coordination and validation of package reproducibility based on hidden votes to limit collusion and a reward scheme to ensure collaboration. The protocol uses the Hyperledger Fabric blockchain as supporting infrastructure, gaining the benefits of high availability, integrity of results and decision traceability from its decentralized nature. To test the protocol, a formal specification was written in TLA+ and validated through model checking. The results showed that, at least for the tested networks, the protocol produces valid results and enforces collaboration between users. Next steps for the project would be to build a functional prototype of the system to test its performance characteristics as well as studying the system actor assumptions made in the protocol design. / Likt hotet från leveranskedjeattacker har ökat, ökar även behoven av skyddstekniker för att säkerställa riktigheten hos mjukvara. Ett sådant typ av skydd ges av reproducerbara byggen. Om ett mjukvarupaket kan byggas exakt likadant varje gång så möjliggör det för användare att upptäcka om paketet har förändrats trots att dess källkod inte har gjort det. Att kunna veta vilka paket som är reproducerbara och därmed lättar att lita på är således en central del i denna skyddsmekanism. Nuvarande strategier för validering och distribution av sådan information bygger på arbete från ett fåtal individer och organisationer med begränsad koordinering däremellan. Detta leder till förvirring för användare på grund av bristen av en central tillitspunkt eller auktoritet. Detta arbete beskriver ett protokoll för decentralizerad koordinering och validering av paketreproducerbarhet baserat på hemliga röster för att begränsa otillåtet samarbete och ett belöningssystem för att motivera önskat samarbete. Protokollet använder blockkedjan Hyperledger Fabric som grund, med fördelarna av att få hög tillgänglighet, resultatsriktighet och spårbara beslut. En formel specifikation skrevs i TLA+ för att testa protokollet och validerades med modeltestning. Testresultatet för de testade nätverkskonfigurationerna visade att protokollet genererar valida resultat och garanterar samarbete mellan användare. De nästa stegen i projektet skulle vara att bygga en funktionell prototyp av systemet för att testa dess prestanda såväl som att studera de antaganden protokollet är designat runt.

Blockchain seems to be the hot new innovation that brings disruption to many different industries in the form of decentralization. Groups of peers can finally organize and work together without a central actor having an authority over the transactions that occur. Other than decentralization, due to the distributed and cryptographic nature of the data, the system also enjoys resilience, immutability and safety. In this thesis, we are leveraging permissioned blockchain technology to take steps towards a trustless service level agreement (SLA) management system where both service providers and customers lack the power to tamper with the contracts and their outcomes. The thesis yields a systematic literature review on the state-of-the-art within SLA management and relevant blockchain technology, a proof-of-concept working with Ericssons decentralized edge service marketplace, Nubo, and finally asimulation which evaluates how the proof-of-concept performs in terms of throughput and latency under different network loads. The simulation shows that the network works as expected, until 70 transactions per second (TPS) are reached, at which point the network is limited by throughput. / Blockchain ser ut att vara den nya teknologin som leder till stora förändringar i olika industrier i form av decentralisering. En grupp av noder kan till slut organisera sig och arbeta tillsammmans utan en central figur som styr och har kontroll över arbetet. Utöver decentralisering ger blockchain också fördelen av uthållighet, oföränderlighet och säkerhet till systemet tack vare sin kryptografiska grund. I den här studien utnyttjar vi privat blockchainteknologi för att ta steg mot en decentraliserad service level agreement (SLA) platform, där både tjänsteleverantörer och konsumenter saknar makten att manipulera kontrakt och dess resultat. Studien ger en systematisk literaturstudie på state-of-the-art inom SLA och relevant blockchain teknologi, ett bevis på koncept som fungerar tillsammans med Ericssons decentraliserade Nubo Service Marknad, och till slut en simulation som undersöker hur systemet reagerar i form av genomströmmning och responstid under olika nätverksbelastningar. Undersökningen visar att nätverket fungerar som förväntat upp till 70 transaktioner per sekund, då nätverket begränsas av genomströmning och köer bildas.

abstract: Blockchain technology enables a distributed and decentralized environment without any central authority. Healthcare is one industry in which blockchain is expected to have significant impacts. In recent years, the Healthcare Information Exchange(HIE) has been shown to benefit the healthcare industry remarkably. It has been shown that blockchain could help to improve multiple aspects of the HIE system. When Blockchain technology meets HIE, there are only a few proposed systems and they all suffer from the following two problems. First, the existing systems are not patient-centric in terms of data governance. Patients do not own their data and have no direct control over it. Second, there is no defined protocol among different systems on how to share sensitive data. To address the issues mentioned above, this paper proposes MedFabric4Me, a blockchain-based platform for HIE. MedFabric4Me is a patient-centric system where patients own their healthcare data and share on a need-to-know basis. First, analyzed the requirements for a patient-centric system which ensures tamper-proof sharing of data among participants. Based on the analysis, a Merkle root based mechanism is created to ensure that data has not tampered. Second, a distributed Proxy re-encryption system is used for secure encryption of data during storage and sharing of records. Third, combining off-chain storage and on-chain access management for both authenticability and privacy. MedFabric4Me is a two-pronged solution platform, composed of on-chain and off-chain components. The on-chain solution is implemented on the secure network of Hyperledger Fabric(HLF) while the off-chain solution uses Interplanetary File System(IPFS) to store data securely. Ethereum based Nucypher, a proxy re-encryption network provides cryptographic access controls to actors for encrypted data sharing. To demonstrate the practicality and scalability, a prototype solution of MedFabric4Me is implemented and evaluated the performance measure of the system against an already implemented HIE. Results show that decentralization technology like blockchain could help to mitigate some issues that HIE faces today, like transparency for patients, slow emergency response, and better access control. Finally, this research concluded with the benefits and shortcomings of MedFabric4Me with some directions and work that could benefit MedFabric4Me in terms of operation and performance. / Dissertation/Thesis / Masters Thesis Computer Engineering 2020

abstract: Microlending aims at providing low-barrier loans to small to medium scaled family run businesses that are financially disincluded historically. These borrowers might be in third world countries where traditional financing is not accessible. Lenders can be individual investors or institutions making risky investments or willing to help people who cannot access traditional banks or do not have the credibility to get loans from traditional sources. Microlending involves a charitable cause as well where lenders are not really concerned about what and how they are paid. This thesis aims at building a platform that will support both commercial microlending as well as charitable donation to support the real cause of microlending. The platform is expected to ensure privacy and transparency to the users in order to attract more users to use the system. Microlending involves monetary transactions, hence possible security threats to the system are discussed. Blockchain is one of the technologies which has revolutionized financial transactions and microlending involves monetary transactions. Therefore, blockchain is viable option for microlending platform. Permissioned blockchain restricts the user admission to the platform and provides with identity management feature. This feature is required to ensure the security and privacy of various types of participants on the microlending platform. / Dissertation/Thesis / Masters Thesis Software Engineering 2020

On-boarding refers to bringing in an employee to a company and granting access to new hires. However, a person may go through different stages of employment, hold different jobs by the same employer and have different levels of information access during the employment duration. A shared services organization may have either limited or wide-spread access within certain groups. Off-boarding implies the removal of access of information or physical devices such as keys, computers or mobile devices when the employee leaves. Off-boarding is the management of the separation an employee from an institution. Many organizations use different steps that constitute the off-boarding process. Incomplete tracking of an employee's access is a security risk and can lead to unintended exposure of company information and assets. Blockchain technology combines blocks of information together using a cryptographic algorithm based on the existing previous block and is verified by the peers in the blockchain network. This process creates an immutable record of employee system access providing an audit trail of access for any point in time to ensure that all access permissions can be removed once employment ends. This project proposes using blockchain technology to consolidate information across disparate groups, and to automate access removal to improve the employee off-boarding process.