Blockchain Papers

Odysseas Lamtzidis, John Gialelis

Internet of Things (IoT) is the current technological breakthrough, enabling computing and sensing devices embedded in everyday processes to seamlessly exchange data, thus shaping the smart-everything concept. Alongside IoT, blockchain is transforming Internet by enabling Trustless, Distributed and Secure exchange of everything of value. In this paper, we propose a distributed sensor node system that utilizes IOTA protocol, a novel distributed ledger technology, to exchange data in an M2M fashion and establish a data monetization economy paradigm.

Xiaoyang Zhu, Youakim Badr

The Internet of Things aims at connecting everything, ranging from individuals, organizations, and companies to things in the physical and virtual world. The digital identity has always been considered as the keystone for all online services and the foundation for building security mechanisms such as authentication and authorization. However, the current literature still lacks a comprehensive study on the digital identity management for the Internet of Things (IoT). In this paper, we firstly identify the requirements of building identity management systems for IoT, which comprises scalability, interoperability, mobility, security and privacy. Then, we trace the identity problem back to the origin in philosophy, analyze the Internet digital identity management solutions in the context of IoT and investigate recent surging blockchain sovereign identity solutions. Finally, we point out the promising future research trends in building IoT identity management systems and elaborate challenges of building a complete identity management system for the IoT, including access control, privacy preserving, trust and performance respectively.

Joshua Ssebunnya, S. Kangere, James Mugisha, Sumaiyah Docrat · 7 authors

BACKGROUND: In spite of the pronounced adverse economic consequences of mental, neurological, and substance use disorders on households in most low- and middle-income countries, service coverage and financial protection for these families is very limited. The aim of this study was to generate potential strategies for sustainably financing mental health care in Uganda in an effort to move towards increased financial protection and service coverage for these families. METHODS: The process of identifying potential strategies for sustainably financing mental health care in Uganda was guided by an analytical framework developed by the Emerging Mental health systems in low and middle income countries (EMERALD project). Data were collected through a situational analysis (public health burden assessment, health system assessment, macro fiscal assessment) and eight key informant interviews with selected stakeholders from sectors including health, finance and civil society. The situational analysis provided contextualization for the strategies, and was complimented by views from key informant interviews. RESULTS: Findings indicate that the following strategies have the greatest potential for moving towards more equitable and sustainable mental health financing in the Uganda context: implementing National Health Insurance Scheme; shifting to Results Based Financing; decentralizing mental health services that can be provided at community level; and continued advocacy with decision makers with evidence through research. CONCLUSION: Although several options were identified for sustainably financing mental health care in Uganda, the National Health Insurance Scheme seemed the most viable option. However, for the scheme to be effective, there is need for scale up to community health facilities and implementation in a manner that explicitly includes community level facilities.

W. K. Chan, Bo Jiang

In this paper, we report our project Fuse, which is a fuzz testing service. It presents the Fuse architecture, and discusses the progress and technical issues to be addressed to fuzz-test smart contracts and support fuzz-testing of Dapps.

Huma Pervez, Muhammad Muneeb, Muhammad Irfan, Irfan Ul Haq

Blockchain is a shared distributed ledger that promises tamper-proof secure transactions over the highly available and resilient network involving multiple participants. Directed Acyclic Graph (DAG) has revolutionized the blockchain technology. Owing to its optimized validation mechanism, high scalability, efficient provenance, support for IoT and multiparty involvement, DAG is rapidly over-shadowing traditional blockchain architecture. In this paper, we present a comparative analysis of most popular DAG based blockchain architectures including Nxt, IOTA, Orumesh, DagCoin,Byteball, Nano and XDAG. The comparison is based on the functional data structures for maintaining the ledger, consensus algorithms, transaction validation, ledger size, scalability and popularity. Extracting the best features various DAG based blockchains, we move on to outline the best of all worlds DAG-based blockchain architecture.

Xuhui Chen, Jinlong Ji, Changqing Luo, Weixian Liao · 5 authors

With the onset of the big data era, designing efficient and effective machine learning algorithms to analyze large-scale data is in dire need. In practice, data is typically generated by multiple parties and stored in a geographically distributed manner, which spurs the study of distributed machine learning. Traditional master-worker type of distributed machine learning algorithms assumes a trusted central server and focuses on the privacy issue in linear learning models, while privacy in nonlinear learning models and security issues are not well studied. To address these issues, in this paper, we explore the blockchain technique to propose a decentralized privacy-preserving and secure machine learning system, called LearningChain, by considering a general (linear or nonlinear) learning model and without a trusted central server. Specifically, we design a decentralized Stochastic Gradient Descent (SGD) algorithm to learn a general predictive model over the blockchain. In decentralized SGD, we develop differential privacy based schemes to protect each party’s data privacy, and propose an l-nearest aggregation algorithm to protect the system from potential Byzantine attacks. We also conduct theoretical analysis on the privacy and security of the proposed LearningChain. Finally, we implement LearningChain on Etheurum and demonstrate its efficiency and effectiveness through extensive experiments.

Huan Zhou, Cees de Laat, Zhiming Zhao

Cloud Service Level Agreement (SLA) is challengeable due to lacking a trustworthy platform. This paper presents a witness model to credibly enforce the cloud service level agreement. Through introducing the witness role and using the blockchain based smart contract, we solve the trust issues about who can detect the service violation, how the violation is confirmed and the compensation is guaranteed. In this model, a verifiable consensus sortition algorithm proposed by us is firstly leveraged to select independent witnesses to form a witness committee. They are responsible for a specific service level agreement and get paid by monitoring and detecting service violation. Through carefully designing the witness' payoff function in the agreement, we further leverage game theory to analyze and prove that it is not the witness itself is trustworthy. Instead, the witness has to tell the truth because of its greedy nature, which is the desire to maximize its own revenue. As long as the service violation is confirmed by the witness committee, the compensation is automatically transferred to the customer by the smart contract. Finally, we implement a proof-of-concept prototype with the smart contract of Ethereum blockchain. It demonstrates the feasibility of our model.

Giovanni Ciatto, Stefano Mariani, Andrea Omicini

Blockchain technologies are rapidly gaining attention in the multi-agent systems (MAS) community to face critical issues such as trust, secured communications, and data consistency. In particular, the notion of smart contract can be exploited to deploy trustworthy computations automatically executed by the network in a consistent way. MAS coordination - modelling and engineering of agents interaction in a MAS - thus represents an appealing application field for smart contracts, potentially enabling fully-decentralised, trustworthy coordination. Along this line, we focus on the Ethereum blockchain technology, map it onto LINDA tuple-based coordination model, and discuss two proof-of-concept implementations of LINDA on Ethereum. We hence demonstrate conceptual and technical feasibility of blockchain-based coordination in MAS, while emphasising issues of applying the blockchain beyond accountability and identity management.

Mehmet Levent Erdaş, Abdullah Emre Çağlar

This study investigates the asymmetric causal relations between Bitcoin and gold, Brent oil, US dollar, S&P 500 and BIST 100 Indexes for the weekly data of the period between November 2013 and July 2018 via by Hatemi-J (2012) test. The results indicate only a causal link going from the Bitcoin price to S&P 500 Index. Consequently, a change in Bitcoin prices appears to influence the investors’ decisions on the S&P 500 Index. Therefore, it can be said that the investors in S&P 500 Index have closely followed the new macro-financial developments in the market and have been active on the S&P 500 market. However, the presence of a causality relation between Bitcoin price and other variables cannot be determined. Thus, it is supposed that Bitcoin may exist in association with the commodity market and other global indicators in the future, along with the recognition of the Bitcoin currency by countries, its being accepted as a means of exchange and its increased reliability.

Shaily Roy, Samiha Nanjiba, Amitabha Chakrabarty

Over the past few years, Bitcoin has been a topic of interest of many, from academic researchers to trade investors. Bitcoin is the first as well as the most popular cryptocurrency till date. Since its launch in 2009, it has become widely popular amongst various kinds of people for its trading system without the need of a third party and also due to high volatility of Bitcoin price. In this paper, we propose a suitable model that can predict the market price of Bitcoin best by applying a few statistical analysis. Our work is done on four year's bitcoin data from 2013 to 2017 based on time series approaches especially autoregressive integrated moving average (ARIMA) model and the work finally could acquire an accuracy of 90% for deciding volatility in weighted costs of bitcoin in the short run.

Anil Gaihre, Yan Luo, Hang Liu

The pseudonymous nature of Bitcoin has sparked the twin rivaling researches in Bitcoin community, that is, either protecting or attacking anonymity. In spite of this intense battle, the answer to a primary question is absent – Do Bitcoin users themselves care about anonymity? This paper demystifies this doubt via analyzing the Bitcoin transaction graphs with the following three contributions: 1). We outline three representative metrics that can signify whether users concern about anonymity. 2). We examine the collective trend of anonymity concerns from a macroscope. 3). We pay particular attention on critical addresses in a microscope to unveil their anonymity concerns.This paper arrives at both expected conclusions and unexpected surprises. In particular, the expected ones are: rich addresses concern more about anonymity than poor ones. Miner addresses start caring about anonymity when exchange rate soars. Stock addresses never hide their intent of jump-and-dump. The surprises are: the majority of the users show weak concerns on anonymity. One can easily find both hot and cold wallet addresses owned by big organizations.

Edward Yi Chang, Shih-Wei Liao, Chun‐Ting Liu, Wei-Chen Lin · 8 authors

This paper presents requirements to DeepLinQ and its architecture. DeepLinQ proposes a multi-layer blockchain architecture to improve flexibility, accountability, and scalability through on-demand queries, proxy appointment, subgroup signatures, granular access control, and smart contracts in order to support privacy-preserving distributed data sharing. In this data-driven AI era where big data is the prerequisite for training an effective deep learning model, DeepLinQ provides a trusted infrastructure to enable training data collection in a privacy-preserved way. This paper uses healthcare data sharing as an application example to illustrate key properties and design of DeepLinQ.

Thawatchai Chomsiri, Kan Kongsup

Various types of cryptocurrency e.g. BitCoin, Ethereum, Zcash, and more, are broadly accepted and used in many different forms of business but a typical problem that the cryptocurrency users are faced with is the delay of coin transfer. For example, it takes several hours for BitCoin and several minutes for Ethereum. These cryptocurrencies also consume a high quantity of electricity for transaction validation. Even though there currently is a type of cryptocurrencies, Ripple, that can be quickly transferred in 4 seconds but still it is a closed system with an owner, not a public cryptocurrency. Similarly, an algorithm "Proof of Stake" used by new coins that are more energy-saving but several problems are still found including (1) 51% attack, (2) a richer with more coins gains higher rewards, and (3) a problematic node for block validation that is not currently active. This research presents a model of an open cryptocurrency system that is able to transfer a coin within 3 seconds in which an algorithm called "Random-Checkers Proof of Stake" (RCPoS) was proposed to randomly select the inspectors for validation processes which can avoid those three problems of the Proof of Stake.

Wai Yan Maung Maung Thin, Naipeng Dong, Guangdong Bai, Jin Dong

Blockchain technology relies on consensus algorithms to resolve conflicts in Byzantine environments. New blockchain algorithms are rapidly designed and implemented without a properly conducted formal analysis and verification. In this paper, we conducted a study on Tendermint which is a proof-of-stake consensus algorithm. We verified that the consensus protocol is deadlock-free and is able to reach consensus when at least 2/3 of the network is in agreement. We also proved that a minority set of nodes that compose more than 1/3 of the network is enough to censor the majority of the network and prevent the network from reaching consensus and conclude that the algorithm has some shortcomings on availability.

Lars Pilgaard Mikkelsen, Kasper Mortensen, Henrik Rasmussen, Hans-Peter Schwefel · 5 authors

Usage of IoT marketplaces as central components in distributed systems have become common, as they allow for easy exploitation of other services and data sources. When relying on a marketplace to be available in order for a system to be operational, it is critical that the marketplace operation is highly robust. Marketplaces are typically centralized components which means that single point of failure is a possible issue. Also users of the marketplace must trust the operator to be fair and follow a common set of rules. This work proposes to utilize blockchain technology to realize a distributed marketplace where both functionalities and storage are distributed and thereby increasing availability to users, while removing the need for a central operator. The blockchain also makes the operational rules transparent to the users of the marketplace. In this relation two core marketplace functionalities, offering creation and discovery, are realized using smart contracts on a private Ethereum blockchain and evaluated using an experimental testbed. The results demonstrate the feasibility of a blockchain based marketplace implementation.

Daniel Fullmer, A. Stephen Morse

This paper presents a stochastic model for block arrival times based on the difficulty retargeting rule used in Bitcoin, as well as other proof-of-work blockchains. Unlike some previous work, this paper explicitly models the difficulty target as a random variable which is a function of the previous block arrival times and affecting the block times in the next retargeting period. An explicit marginal distribution is derived for the time between successive blocks (the blocktime), while allowing for randomly changing difficulty. This paper also aims to serve as an introduction to Bitcoin and proof-of-work blockchains for the controls community, focusing on the difficulty retargeting procedure used in Bitcoin.

Natalia Chaudhry, Muhammad Murtaza Yousaf

Blockchain is a distributed ledger that gained a prevalent attention in many areas. Many industries have started to implement blockchain solutions for their application and services. It is important to know the key components, functional characteristics, and architecture of blockchain to understand its impact and applicability to various applications. The most well-known use case of blockchain is bitcoin: a cryptocurrency. Being a distributed ledger, consensus mechanism is needed among peer nodes of a blockchain network to ensure its proper working. Many consensus algorithms have been proposed in literature each having its own performance and security characteristics. One consensus algorithm cannot serve the requirements of every application. It is vital to technically compare the available consensus algorithms to highlight their strengths, weaknesses, and use cases. We have identified and discussed parameters related to performance and security of consensus in blockchain. The consensus algorithms are analyzed and compared with respect to these parameters. Research gap regarding designing an efficient consensus algorithm and evaluating existing algorithms is presented. This paper will act as a guide for developers and researchers to evaluate and design a consensus algorithm.

Michel Cannarsa

Abstract: The computer language (computer code) on the basis of which smart contracts are written is different from the natural (Human) language. Computer language is a ‘dry’ language, whereas natural language is ‘wet’. In other words, it means that computer language is deterministic (just one meaning and one result are conceivable), when natural language is open to more and potential different meanings. Natural language requires therefore in itself interpretation, at least more than computer language. Computer language in theory doesn’t require and possibly doesn’t leave room for interpretation. If this assumption is accurate, what are the consequences of it (on the intention of the parties, on contract drafting, on courts’ intervention…)? Building on that assumption, this article explores, from a comparative perspective, the impact of the blockchain-based smart contract technology, especially regarding contract drafting techniques. Contract drafting style in common law (long contracts, based on a ‘if …, then ….’ approach, quite similar to the coding approach) is in part based on the idea of preventing courts’ interpretation and intervention. In civil law countries instead, contracts are generally shorter, for several reasons but partly because drafters tend to rely on more general legal concepts, external to the contract, and know that courts will play an important role, through interpretation, in disclosing the ‘true meaning’ of a contract. Coding contracts and relying on computer-code language can hence have a significant impact on the civil law approach and bring the two legal systems closer as far as contract drafting and contract interpretation are concerned.

Rafael Brundo Uriarte, Rocco De Nicola, Kyriakos Kritikos

Cloud services operate in a highly dynamic environment. This means that they need to be assorted with dynamic SLAs which explicate how a rich set of QoS guarantees evolves over time. Only in this way, cloud users will trust and thus migrate their processes to the cloud. Research-wise, SLAs are assumed to include single states while they are managed mainly in a centralised manner. This paper proposes a framework to manage dynamic SLAs in a distributed manner by relying on a rich and dynamic SLA formalism which is transformed into a smart contract. This contract is then handled via the blockchain which exploits an oracle-based interface to retrieve the off-chain cloud service context sensed and enforce the right SLA management/modification functions. The proposed framework can change the current shape of the cloud market by catering for the notion of an open distributed cloud which offers manageable and dynamic services to cloud customers enabling them to reduce costs and increase the flexibility in resource management.

André Janssen, Mateja Djurovic

Abstract: This contribution examines the formation of (blockchain-based) smart contracts. The term smart contract is used to refer to software programmes which are often, but not necessarily, built on blockchain technology as a set of promises, specified in digital form, including protocols within which the parties perform on these promises. It is regularly said that smart contracts are neither legal contracts in the traditional sense nor they are smart and that the term is therefore a misnomer. The crucial question this article is trying to answer is whether the traditional common law concept of contract formation is seriously challenged by the rise of smart contracts. As such, are smart contracts marking the end of contract formation as we know it or is it just much ado about nothing? Résumé: Cette contribution examine la formation de contrats intelligents (basés sur la blockchain). Le terme de contrat intelligent est utilisé pour faire référence aux programmes de software qui sont souvent, mais pas nécessairement, conçus sur la technologie de la blockchain comme un ensemble de promesses, spécifiées sous forme digitale, comprenant des protocoles au sein desquels les parties accomplissent ces promesses.On a souvent dit que les contrats intelligents ne sont ni des contrats juridiques au sens traditionnel ni intelligents et que le terme est donc inapproprié. La question cruciale à laquelle le présent article tente de répondre est de savoir si le concept traditionnel dans la common law de la formation du contrat est sérieusement mis au défi par l’arrivée des contrats intelligents. Comme tels, les contrats intelligents marquent-ils la fin de la formation des contrats telle que nous la connaissons ou ne s’agit-il finalement que de ‘beaucoup de bruit pour rien’?

Jack Gilcrest, Arthur Carvalho

In this paper, we analyze the value of smart contracts and blockchains as an alternative to traditional contractual obligations. In particular, we start by exploring some of the advantages of these technologies, specifically the immutability of blockchains and automated contract remittance. We also discuss two critical shortcomings of decentralized smart contracts, namely regulatory uncertainty and a lack of confidential execution. With these issues in mind, we next explore how American legislators have begun to address smart contracts and blockchains. Though quite limited, there have been a few provisions clarifying the status of these technologies. We break down some of the language expressed in these bills so as to understand the current legal status of smart contracts and blockchains. Given this foundation, we consider the next steps that should be taken as smart contracts mature. This pertains to both the continued improvement of the underlying technology as well as the progress taken by regulators. Finally, assuming a futuristic scenario where there are no technological or regulatory barriers to smart contract adoption, we discuss how the process of contract remittance can be expedited in a world fully committed to the use of smart contracts.

Lennart Bader, Jens Bürger, Roman Matzutt, Klaus Wehrle

Processes in the insurance economy are often cumbersome and expensive because of the inherently opposing interests of insurers and customers. Smart contracts bear a large potential to simplify these processes and thereby reduce costs. In this paper, we present CAIPY, our smart contract-based ecosystem for simple and transparent car insurance. In CAIPY, smart contracts do not replace but support current processes to enable significant cost savings, e.g., by removing the necessity for manual inspection of insurance claims in presence of tamper-resistant car sensors. However, the involved parties can resort to well-established processes at any time, trading off cost efficiency against process reliability. CAIPY thus showcases how smart contracts can support insurers without introducing new risks.

Riccardo de Caria

Abstract: This article investigates the legal dimension of smart contracts. In particular, it reviews their existing definitions in some of the main laws enacted and scholarly articles published to date, proposes its own version, to then move on to consider to what extent new legal categories are warranted to deal with this apparently totally new way of making legally binding agreements. It concludes by providing some final remarks with regard to relevant legal categories and attempts to advance a number of solutions to the legal questions raised by the application of smart contracts. Résume: Le présent article étudie la dimension juridique de contrats intelligents. En particulier, il passe en revue leurs définitions qui se trouvent dans certaines des lois essentielles promulguées et dans des articles académiques publiés jusqu’à présent, il propose sa version propre, et considère ensuite dans quelle mesure de nouvelles catégories juridiques sont justifiées pour traiter cette manière apparemment tout à fait nouvelle de passer des accords juridiquement obligatoires. Il conclut par quelques remarques finales concernant des catégories juridiques importantes et tente d’apporter certaines solutions aux questions juridiques soulevées par l’application de contrats intelligents.

Hoai Luan Pham, Thi Hong Tran, Yasuhiko Nakashima

Nowadays, a combination between Internet of Things (IoT) technology and remote healthcare system is extensively researched due to its efficiency and convenience for human life. When the number of IoT devices in health care system is increased exponentially, the privacy and security issues of patients are becoming a concern. In order to protect personal and device-generated information, we propose to use blockchain-based smart contracts for managing patients' information and medical devices. In detail, using blockchain based on the Ethereum protocol, we create a remote healthcare system including healthcare provider (such as hospital), healthcare professionals (doctors) and patients. Health condition of patients is measured by sensors and such information is written into blockchain automatically. In addition, we propose a processing mechanism to store the medical device information efficiently and sparingly in accordance with health situation of patient. Concretely, we filter the data from sensors before deciding whether to write data into blockchain or not. Doing so we can reduce the size of blockchain as well as save amount of coins for transaction efficiently. However, the abnormal data from sensors will be written to blockchain immediately and trigger an emergency contact to doctor and hospital for on-time treatment. We have verified the proposed smart contract on Ethereum test environment called TESTRPC and implemented the system on an experimental environment with real devices. This system works well at small scale.