京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24151号 / 情博第799号 / 新制||情||135(附属図書館) / 京都大学大学院情報学研究科社会情報学専攻 / (主査)教授 伊藤 孝行, 教授 吉川 正俊, 教授 緒方 広明, 特定准教授 LIN Donghui / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

High-profile outbreaks in the U.S. have been increasingly linked to the consumption of leafy greens (Xue et al. 2007), making traceability an important issue (Corkery and Popper 2018). Consumers' increasing attention to traceability (Hansstein 2014) has led to the implementation of blockchain-based traceability systems. This study measures U.S. consumers' willingness-to-pay (WTP) for blockchain-based traceability information in packages of romaine lettuce and spinach. We conduct two online Discrete Choice Experiments (DCEs) and surveys to understand consumer preferences for USDA-certified organic leafy greens, access to blockchain-based traceability information via QR codes, and the FDA's voluntary labeling guidelines involving growing region information. Our findings suggest that some U.S. consumers are willing to pay a premium for food products with blockchain-based traceability or standard traceability information delivered via QR-codes. Findings also reflect some consumers' interest in organic products, and in knowing the detailed growing region information, particularly if leafy greens are grown in Arizona.

<p>This dissertation investigates the strategic implications of blockchain technologies on interorganizational collaborations. Recently, blockchain technology has been permeating a broad range of industries and impacting how organizations conduct business. Rather than a traditional industrial technology that boosts productivity, blockchain should be viewed as an institutional technology that influences collaborative relationships among business agents. This dissertation endeavors to (partially) answer the overarching question that, from the point of view of cooperative strategies, what are the implications of blockchain technology for those involved organizations?</p> <p>One of the major theoretical arguments of this dissertation is that blockchain technology offers a new way of organizing collaborations. It works as a governance mechanism that is different from traditional social mechanisms—contractual and relational governance. Specifically, it provides a unique approach to enforcing agreements automatically through codes and algorithms. It also differs from other information technologies, such as EDI, in terms of the capacity to enforce agreements and govern collaborations. Furthermore, it acknowledges that blockchain governance has its limits – it can only efficiently organize explicit collaborations while is less efficient on tacit ones. Nevertheless, understanding the new governance logic with blockchain technology has important implications for managers in choosing the right strategic tool to organize collaborative efforts with other organizations.</p> <p>The new organizing approach by blockchain technology also enhances the scalability of governance and enables an increasing number of multiparty collaborations. By reviewing the alliance literature, this dissertation suggests that multiparty collaborations have unique features that deserve separate scholarly attention from well-studied dyadic alliances. Focusing on the increased number of collaborators with blockchain technology, this dissertation investigates the performance heterogeneity of blockchain consortia and its determinants. It challenges the conventional view in the multiparty alliance literature that the number of firms negatively impacts alliance performance. By differentiating between short-term and long-term performance of blockchain consortia, it argues that the compositional characteristics of each blockchain consortium’s founding group have an impact on its performance. Empirical results from a sample of blockchain consortia show that, although the size of the founding group is negatively related to consortium performance in the short term (in terms of the speed to complete piloting), it is positively associated with performance in the longer run (in terms of survival and growth). Specifically, the long-term performance effect is explained by the composition of the founding group, in terms of the diversity of industry sectors and the number of competing ties. The findings have direct implications for scholars and managers in understanding the strategic trade-offs of leveraging the business potentials of blockchain technology.</p>

The digital transformation facilitates new forms of collaboration between companies along the supply chain and between companies and consumers. Besides sharing information on centralized platforms, blockchain technology is often regarded as a potential basis for this kind of collaboration. However, there is much hype surrounding the technology due to the rising popularity of cryptocurrencies, decentralized finance (DeFi), and non-fungible tokens (NFTs). This leads to potential issues being overlooked. Therefore, this thesis aims to investigate, highlight, and address the current weaknesses of blockchain technology: Inefficient consensus, privacy, smart contract security, and scalability. First, to provide a foundation, the four key challenges are introduced, and the research objectives are defined, followed by a brief presentation of the preliminary work for this thesis. The following four parts highlight the four main problem areas of blockchain. Using big data analytics, we extracted and analyzed the blockchain data of six major blockchains to identify potential weaknesses in their consensus algorithm. To improve smart contract security, we classified smart contract functionalities to identify similarities in structure and design. The resulting taxonomy serves as a basis for future standardization efforts for security-relevant features, such as safe math functions and oracle services. To challenge privacy assumptions, we researched consortium blockchains from an adversary role. We chose four blockchains with misconfigured nodes and extracted as much information from those nodes as possible. Finally, we compared scalability solutions for blockchain applications and developed a decision process that serves as a guideline to improve the scalability of their applications. Building on the scalability framework, we showcase three potential applications for blockchain technology. First, we develop a token-based approach for inter-company value stream mapping. By only relying on simple tokens instead of complex smart-contracts, the computational load on the network is expected to be much lower compared to other solutions. The following two solutions use offloading transactions and computations from the main blockchain. The first approach uses secure multiparty computation to offload the matching of supply and demand for manufacturing capacities to a trustless network. The transaction is written to the main blockchain only after the match is made. The second approach uses the concept of payment channel networks to enable high-frequency bidirectional micropayments for WiFi sharing. The host gets paid for every second of data usage through an off-chain channel. The full payment is only written to the blockchain after the connection to the client gets terminated. Finally, the thesis concludes by briefly summarizing and discussing the results and providing avenues for further research. / Die digitale Transformation ermöglicht neue Formen der Zusammenarbeit zwischen Unternehmen entlang der Wertschöpfungskette, sowie zwischen Unternehmen und Verbrauchern. Neben dem Austausch von Informationen auf zentralen Plattformen wird die Blockchain-Technologie häufig als mögliche Grundlage für diese Art der Zusammenarbeit angesehen. Allerdings gibt es auch durch die steigende Popluarität von Cryptowährungen, Decentralized Finance (DeFi) und non-fungible Tokens (NFTs) einen großen Hype um die Technologie. Dieser führt dazu, dass mögliche Probleme übersehen werden. Daher sollen in dieser Thesis die derzeitigen Schwachstellen der Blockchain-Technologie aufgezeigt und ausgewählte Maßnahmen zur Verbesserung aufgezeigt werden. Es werden dabei vier Schwachstellen betrachtet: Ineffizienter Konsens, Datenschutz, Sicherheit von Smart Contracts und Skalierbarkeit. Als Grundlage werden zunächst die vier zentralen Herausforderungen vorgestellt und die Forschungsziele definiert. Es folgt eine kurze Darstellung der Vorarbeiten für diese Arbeit. In den folgenden vier Teilen wird für jedes der vier Hauptproblembereiche von Blockchain ein spezifisches Problem beleuchtet: Ineffizienter Konsens, Datenschutz, Smart-Contract-Sicherheit und Skalierbarkeit. Mit Hilfe von Big-Data-Analytics wurden die Blockchain-Daten von sechs großen Blockchains extrahiert und analysiert, um potenzielle Schwachstellen in deren Konsens-Algorithmus zu identifizieren. Um die Sicherheit von Smart Contracts zu verbessern, wurden die Funktionalitäten von Smart Contracts klassifiziert, um Ähnlichkeiten in Struktur und Design zu identifizieren. Die sich daraus ergebende Taxonomie dient als Grundlage für künftige Standardisierungsbemühungen für sicherheitsrelevante Funktionen, wie z. B. sichere mathematische Funktionen und Orakeldienste. Um die Annahmen von Datenschutz in Frage zu stellen, wurden Konsortialblockchains aus der Angreiferperspektive untersucht. Es wurden vier Blockchains mit falsch konfigurierten Knoten betrachtet mit dem Ziel so viele Informationen wie möglich aus diesen Knoten zu extrahieren. Schließlich wurden Lösungen für die Skalierbarkeit von Blockchain-Anwendungen verglichen und einen Entscheidungsprozess entwickelt, der als Leitfaden für die Verbesserung der Skalierbarkeit ihrer Anwendungen dient. Aufbauend auf dem Skalierbarkeitsframework werden potenzielle Anwendungen für die Blockchain-Technologie vorgestellt. Zunächst wurde einen Token-basierter Ansatz für die Abbildung eines unternehmensübergreifenden Wertstroms entwickelt. Da sich hier nur auf einfache Token anstelle von komplexen Smart-Contracts gestützt wurde, sollte die Rechenlast im Netzwerk im Vergleich zu anderen Lösungen deutlich geringer sein. Die beiden anderen Lösungen nutzen die Auslagerung von Transaktionen und Berechnungen aus der Hauptblockchain heraus. Der erste Ansatz nutzt Secure Multiparty Computation, um das Matching von Angebot und Nachfrage für Produktionskapazitäten in ein vertrauensfreies Netzwerk auszulagern. Erst wenn das Matching erfolgt ist, wird die Transaktion in die Haupt-Blockchain geschrieben. Der zweite Ansatz nutzt das Konzept von Payment Channel Networks, um hochfrequente bidirektionale Micropayments für WiFi-Sharing zu ermöglichen. Der Host wird für jede Sekunde der Datennutzung über einen Off-Chain-Chanel bezahlt. Die vollständige Zahlung wird erst dann in die Blockchain geschrieben, wenn die Verbindung zum Client beendet wird. Zum Abschluss der Arbeit werden die Ergebnisse zusammengefasst, diskutiert und Mög-lichkeiten für weitere Forschungsarbeiten aufgezeigt.

This work addresses the challenge of heterogeneity in blockchain mining, particularly in the context of consortium and private blockchains. The motivation stems from ensuring fairness and efficiency in blockchain technology's Proof of Work (PoW) consensus mechanism. Existing consensus algorithms, such as PoW, PoS, and PoB, have succeeded in public blockchains but face challenges due to heterogeneous miners. This thesis highlights the significance of considering miners' computing power and resources in PoW consensus mechanisms to enhance efficiency and fairness. It explores the implications of heterogeneity in blockchain mining in various applications, such as Federated Learning (FL), which aims to train machine learning models across distributed devices collaboratively. The research objectives of this work involve developing novel RL-based techniques to address the heterogeneity problem in consortium blockchains. Two proposed RL-based approaches, RL based Miner Selection (RL-MS) and RL based Miner and Difficulty Selection (RL-MDS), focus on selecting miners and dynamically adapting the difficulty of PoW based on the computing power of the chosen miners. The contributions of this research work include the proposed RL-based techniques, modifications to the Ethereum code for dynamic adaptation of Proof of Work Difficulty (PoW-D), integration of the Commonwealth Cyber Initiative (CCI) xG testbed with an AI/ML framework, implementation of a simulator for experimentation, and evaluation of different RL algorithms. The research also includes additional contributions in Open Radio Access Network (O-RAN) and smart cities. The proposed research has significant implications for achieving fairness and efficiency in blockchain mining in consortium and private blockchains. By leveraging reinforcement learning techniques and considering the heterogeneity of miners, this work contributes to improving the consensus mechanisms and performance of blockchain-based systems. / Master of Science / Technological Advancement has led to devices having powerful yet heterogeneous computational resources. Due to the heterogeneity in the compute of miner nodes in a blockchain, there is unfairness in the PoW Consensus mechanism. More powerful devices have a higher chance of mining and gaining from the mining process. Additionally, the PoW consensus introduces a delay due to the time to mine and block propagation time. This work uses Reinforcement Learning to solve the challenge of heterogeneity in a private Ethereum blockchain. It also introduces a time constraint to ensure efficient blockchain performance for time-critical applications.

<div><div>The blockchain offers a decentralized way to provide security guarantees for financial transactions. However, this ability comes with the cost of storing a large (distributed) blockchain state and introducing additional computation and communication overhead to all participants. All these drawbacks raise a challenging scalability problem, especially for resource-constrained blockchain clients. On the other hand, some scaling solutions typically require resource-constrained clients to rely on other nodes with higher computational and storage capabilities. However, such scaling solutions often expose the data of the clients to risks of compromise of the more powerful nodes they rely on (e.g., accidental, malicious through a break-in, insider misbehavior, or malware infestation). This potential for leakage raises a privacy concern for these constrained clients, in addition to other scaling-related concerns. This dissertation proposes several cryptographic constructions and system designs enabling resource-constrained devices to participate in the blockchain network securely and efficiently. </div><div><br></div><div>Our first proposal concerns the storage facet for which we propose two add-on privacy designs to address the scaling issue of storing a large blockchain state. </div><div>The first solution is an oblivious database framework, called T³, that allows resource-constrained clients to obliviously fetch blockchain data from potential malicious full clients. The second solution focuses on the problem of using and storing additional private-by-design blockchains (e.g., Monero or ZCash) to achieve privacy. We propose an add-on tumbler design, called AMR, that offers privacy directly to clients of non-private blockchains such as Ethereum without the cost of storing and using different blockchain states.</div><div><br></div><div>Our second proposal addresses the communication facet with focus on payment channels as a solution to address the communication overhead between the constrained clients and the blockchain network. A payment channel enables transactions between arbitrary pairs of constrained clients with a minimal communication overhead with the blockchain network. However, in popular blockchains like Ethereum and Bitcoin, the payment data of such channels are exposed to the public, which is undesirable for financial applications. Thus, to hide transaction data, one can use blockchains that are private by design like Monero. However, existing cryptographic primitives in Monero prevent the system from supporting any form of payment channels. Therefore, we present <i>Dual Linkable Spontaneous Anonymous Group Signature for Ad Hoc Groups (DLSAG),</i> a linkable ring signature scheme that enables, for the first time, off-chain scalability solutions in Monero. </div><div><br></div><div>To address the computation facet, we address the computation overhead of the gossip protocol used in all popular blockchain protocols. For this purpose, we propose a signature primitive called <i>Flexible Signature</i>. In a flexible signature scheme, the verification algorithm quantifies the validity of a signature based on the computational effort performed by the verifier. Thus, the resource-constrained devices can partially verify the signatures in the blockchain transactions before relaying transactions to other peers. This primitive allows the resource-constrained devices to prevent spam transactions from flooding the blockchain network with overhead that is consistent with their resource constraints. </div></div>

Content distribution networks deliver content like videos, apps, and music to users through servers deployed in multiple datacenters to increase availability and delivery speed of content. The motivation of this work is to create a content distribution network that maintains a consumer’s rights and access to works they have purchased indefinitely. If a user purchases content from a traditional content distribution network, they lose access to the content when the service is no longer available. The system uses a peer to peer network for content distribution along with a blockchain for digital rights management. This combination may give users indefinite access to purchased works. The system benefits content rights owners because they can sell their content in a lower cost manner by distributing costs among the community of peers.

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Cryptocurrencies are becoming increasingly popular in the business and financial world. With arguments for and against, people praising it and people demanding a ban, the highest financial returns and the worst economic falls, it is widely discussed and splits the world. This research has taken the focus of experienced Swedish private investors and analyzed the factors that affect their decisions in terms of cryptocurrency investments. Previous research had found patterns within the demographic and strategies of the investors as well as the risks, diversifying or hedging opportunities, and government regulations associated with cryptocurrencies. These findings were used to form semi- structured interviews where the investors would express their opinions and decisions. This resulted in new contributions to the research in terms of the allocation of private investments in cryptocurrencies and the lack of strategy in the investments. Research was also confirmed in terms of government regulations, what drives these risky investments, and the skeptical future of cryptocurrencies.

The purpose of this paper is defined to research the obstacles that hamper the implementation of blockchain technology in Swedish procurement. The identification of a knowledge gap in prior research related to this field is uncovered by substantial literature research. Previous research in this area is mainly conducted with an orientation towards the implementational benefits and design or implementation examples This paper thereby leads to a fulfillment of the discovered knowledge gap and contributes to the field. The research question; “What obstacles hamper the implementation of blockchain technology in the process of public procurement in Sweden?” Exploration of this is conducted through a qualitative research study with a geographical limit set to the country of Sweden. The study is conducted with the use of four different perspectives that consists of professionals with expertise in different fields. Obstacles that could hamper the merger between blockchain technology and procurement are identified, both using categories that are defined in a cross-perspective environment and individual obstacle topics. Further research ideas are also presented suggesting future studies surrounding the obstacle dynamics of this study.