Blockchain Platform Research Articles

A distributed cross-chain mechanism based on notary schemes and group signatures

Blockchain technology has attracted significant attention since its publication. However, most existing blockchain platforms are isolated systems, which makes it difficult to exchange data among different blockchains. The industry has proposed the notary schemes to enhance blockchain interoperability, which can exchange messages among different blockchains through a notary. However, conventional notary schemes are centralized, which suffers from single point of failures. To address these issues, this paper proposes a distributed cross-chain notary model with regulatory mechanisms, based on improved threshold group signatures. We improve the group signature scheme by setting up a group of tracing authorities to achieve distributed tracing. Furthermore, we incorporate this signature scheme into our notary scheme, where a group of notaries signs cross-chain transactions using group signatures. We also introduce a group of regulators to reveal the true identities of malicious notaries when disputes occur. Finally, we prove the security of our signature scheme based on the Random Oracle Model. In our experiments, when the number of notaries is 102 and the threshold is 2/3 of that, it takes 166 ms to set up and generate signature. Also, it takes 161 ms for regulators to reveal the true identities of malicious notaries.

Enhancing Educational Certificate Verification With Blockchain and IPFS: A Decentralized Approach Using Hyperledger Fabric

Educational certificate counterfeiting poses a significant global challenge, demanding urgent attention and robust solutions. This paper addresses the problem of forgery and verification of educational certificates by leveraging blockchain technology as an anti-counterfeiting measure. A decentralized architecture for educational certificate verification systems is proposed and implemented using the Hyperledger Fabric as a blockchain platform and the Inter Planetary File System (IPFS). By utilizing the unique features of these technologies, we aim to establish a reliable and secure system for verifying authenticity of educational certificates without relying on third-party intermediaries. Our approach involves storing educational certificate files on a decentralized file system, namely IPFS, ensuring their integrity and accessibility. To enable efficient verification, each certificate is associated with a certificate ID, which retrieves the necessary validating information from the Hyperledger Fabric network. This integration ensures that educational certificates are securely stored on the blockchain, preventing any tampering attempts and enabling easy validation. The experimental results demonstrate that educational certificates are stored on the Hyperledger Fabric network in a manner that ensures their immutability, making it impossible to alter them. Furthermore, the system allows for verification of their authenticity without the need for any third-party intervention. By combining the power of blockchain technology with IPFS, our solution provides a robust approach to tackle the growing issue of educational certificate counterfeiting. This research contributes to the field by offering a decentralized architecture that enhances the security and trustworthiness of educational certificate verification systems.

Fine-grained Ethereum behavior identification via encrypted traffic analysis with serialized backward inference

Blockchain has developed rapidly in recent years. Asymmetric to the rapid development of the blockchain industry is the backwardness of blockchain regulatory technology. The existing research on blockchain security mainly explores blockchain technology and focuses on analyzing on-chain data. We argue that analyzing blockchain network traffic can provide a new perspective on building behavior patterns and blockchain regulation. Ethereum, as the most applied blockchain platform, has flourished with the maturity of blockchain technology. Monitoring fine-grained Ethereum behaviors is essential for the healthy development of Ethereum. However, different Ethereum behaviors are transmitted in an encrypted and persistent connection and are difficult to segment. Besides, the four Get class behaviors, including getBlockHeaders, getNodeData, getReceipts, and getBlockBodies, are indistinguishable from Ethereum traffic. This work proposes a Fine-grained Ethereum Behavior Identification system via encrypted traffic analysis with Serialized Backward Inference, dubbed FEBI-SBI. FEBI-SBI first performs Ethereum behavior traffic segmentation using packets with a load length of 32 Bytes and ACK values larger than their preceding packets in the same direction as the segmenting points. Then, the flow segments for Ethereum behaviors are fed to machine learning classifiers to perform coarse-grained Ethereum behavior identification. Finally, for the Get class behaviors indistinguishable by the machine learning classifiers, FEBI-SBI applies behavior serialized backward inference to identify them from their corresponding fine-grained Send class behaviors identified by the machine learning classifiers. Our experimental results demonstrate the effectiveness and efficiency of FEBI-SBI in identifying fine-grained Ethereum behaviors. FEBI-SBI can be applied to effectively identify anomaly behaviors on the Ethereum network and thus enable the regulation of Ethereum users.

Digital information in maritime supply chains with blockchain and cloud platforms: Supply chain capabilities, barriers, and research opportunities

Digital transformation plays a key role in improving information sharing and information processing in supply chains. Specifically, maritime supply chains require numerous data and document exchanges and can significantly benefit from digital information sharing (DIS). This notable potential has attracted attention and has resulted in a growing number of studies on blockchain platforms, cloud-based platforms, and other digital technology platforms. However, DIS adoption and execution is a complex process as it depends on various success factors and barriers and affects numerous capabilities and performance outcomes. Moreover, various information systems and management theories can be utilised to underpin these relationships. Our study aims to conduct a systematic literature review that uncovers dynamic capabilities, barriers, enablers and outcomes of DIS with blockchain and cloud-based platforms, illustrates the relationship between them, and discloses methods and theories applied in supply chains. We discuss different use cases of blockchain and cloud-based platforms for DIS in various business functions in supply chains. Particularly, we reveal six DIS-powered capabilities, five performance outcomes improved by the DIS, eight main barriers, and nine enablers of DIS implementation. The lack of theoretical underpinning and causal empirical studies is identified as an important gap in the literature. This study also presents precise future research directions that can help address these gaps.

How blockchain technology supports the business processes of clinical trials: a systematic review

PurposeThe authors propose a blockchain platform for managing clinical trial data to enhance data validity, integrity, trust and transparency in the pharmaceutical research process. The authors also provide an extensive review of how blockchain technology supports the business processes of clinical trials.Design/methodology/approachA systematic literature review was conducted to identify the existing applications of blockchain in pharmaceutical process management. A conceptual design for a blockchain infrastructure to address clinical trial challenges is developed by outlining the entire clinical trial value chain and identifying the coordination and communication among its stakeholders. A stakeholder analysis is conducted to ensure that the clinical trial processes satisfy the requirements and preferences of each stakeholder.FindingsThe proposed blockchain platform offers a promising solution for enhancing integrity, trust and transparency in the clinical trial process. Additionally, blockchain can help streamline communication and collaboration between stakeholders by enabling multiple parties to access and share data in real time, lowering the possibility of delays or errors in data analysis and reporting.Practical implicationsThe proposed blockchain platform can benefit patients by empowering them to have better-controlled access to their data and by allowing researchers to maintain adherence to reporting requirements. Additionally, the platform can benefit granting agencies, researchers and decision-makers by ensuring the integrity of clinical trial data and streamlining communication and collaboration between stakeholders.Originality/valueThis study builds on existing blockchain applications in pharmaceutical process management by developing a blockchain framework that can address clinical trial concerns from an integrated perspective.

Blockchain adoption strategy of two-sided shipping platforms connecting forwarder and liner company

Blockchain technology has already been explored and used in many industries, while the shutdown of shipping blockchain platform TradeLens poses a substantial challenge to the blockchain adoption in the shipping supply chain. Motivated by this practical issue, we develop a Hotelling model to study two competitive shipping platforms’ pricing strategies and blockchain technology investment preferences in three scenarios including both shipping platforms invest nothing, only one shipping platform invests, as well as both shipping platforms invest. The liner companies and forwarders in the two-sided markets may join only one shipping platform (i.e., singlehoming) or join two shipping platforms simultaneously (i.e., multihoming). Our results suggest that whether the blockchain technology is introduced or not, the shipping platforms in each scenario provide the pricing strategies via subsidizing and charging the entry fees for the liner companies and forwarders when singlehoming occurs, whereas the only pricing strategy is to demand the entry fees when multihoming occurs. Moreover, we find that the shipping platforms’ investment preferences over blockchain technology would not be affected by the liner companies’ and forwarders’ singlehoming or multihoming behavior. The shipping platform without blockchain technology investment can achieve profit improvement by free riding via the other shipping platform’s blockchain investment decision given certain investment cost, while the shipping platform with blockchain technology investment instead suffers a loss of profitability due to its investment decision. In particular, compared to singlehoming, the shipping platforms may obtain higher equilibrium profits when multihoming occurs among three scenarios.

Simondon, Control and the Digital Domain

Deleuze put forth a description of fluid control in computerized society in his text ‘Postscript on Control Societies’. With the help of the philosophy of Gilbert Simondon, we can broaden and complexify this view and understand digital systems through the concept of modulation. These modulatory systems intervene in human individuation by controlling individuals as ‘dividuals’. In contemporary digital technologies, like blockchain platforms, the modulatory dividual control can be fierce and even total. Simondon’s concepts of pre-individual, individuation, and transindividuation present us with an ontology for this contemporary mode of control and enable us to better understand the complex relations between the being of humans and technical networks.

Blockchain-based biometric identity management

In recent years, face biometrics recognition systems are a wide space of a computer usage which is mostly employed for security purpose. The main purpose of the face biometrics recognition system is to authenticate a user from a given database. Due to the widespread expansion of the surveillance cameras and facial recognition technology, a robust face recognition system required. The recognition system needs to store a large number of training samples in any storage unit, that time hackers can access and control that data. So, Protecting and managing sensitive data is essential object. This requires a technique that preserve the privacy of individuals, maintain data integrity, and prevent information leakage. The storage of biometric templates on centralized servers has been associated with potential privacy risks. To address this issue, we have developed and implemented a proof-of-concept facial biometric identification system that uses a private Blockchain platform and smart contract technology. So, the proposed approach is presented a secure and tamper-proof from data breaches as well as hacks with data availability, by using the Blockchain platform to store face images. This paper aims to utilize Blockchain technology to identify individuals based on their biometric traits, specifically facial recognition system makes it tamper-proof (immutable) ensuring security. The system consists of enrolment and authentication phases. Blockchain technology uses peer-to-peer communication, cryptography, consensus processes, and smart contracts to ensure the security. The proposed approach was tested on two popular datasets: CelebFaces Attributes (CelebA) and large-scale face UTKFace datasets. The experimental results indicate that the system yields highly performance outcomes, as evidenced by the Equal Error Rate (EER) values of 0.05% and 0.07% obtained for the CelebA and UTKFace datasets, respectively. The system was compared to three baseline methods and scored the lowest Equal Error Rate.

Smart and Secure Blockchain Structure to Track Vehicle Record-keeping in the Sultanate of Oman

In the country of Sultanate of Oman, the Royal Oman Police (ROP) is responsible for carrying out the Inspection, Registration/Renewal, Transfer of ownership, Licensing of a vehicle and the Investigation of traffic accidents. The traditional system used for storing this information does not guarantee whether any information has been tampered with or manipulated. Having a tamper-proof methodology like Blockchain to capture this important information in a distributed ledger register can enable all the participants in the Registration Chain (Supplier of the vehicle, Owner of the vehicle, various Government Agencies and public at large) to gain confidence, build trust and authenticate records that are maintained by the centralised agency. In this paper, a groundbreaking solution built on Hyperledger Besu, a permissioned Ethereum blockchain platform, is introduced that offers a revolutionary approach to vehicle registration and management. It ensures secure and immutable vehicle registration, utilizing IPFS for document storage and ERC-20 tokens to track vehicle history. This Ethereum-powered system facilitates transparent ownership transfers, comprehensive vehicle history tracking, streamlined insurance renewals, seamless vehicle inspections, real-time tracking, and blockchain-based verification, all contributing to heightened efficiency and trust in vehicle processes for the Omani government. By integrating blockchain technology, this solution addresses the challenges of data integrity, security, and transparency that have long plagued the vehicle registration and transfer processes in Oman. This paper highlights the potential of blockchain to revolutionize governmental services and improve the overall efficiency and trustworthiness of vehicle-related transactions, ultimately benefiting both the government and citizens alike.

IoT Applications, Platforms, Systems, And Framework based on Blockchain

The Internet of Things (IoT) has lately evolved as a new technology capable of providing real-time and cutting-edge sensing capabilities to numerous industries such as healthcare, agriculture, smart cities, smart homes, and supply chain. Because of this technology's inherent promise, it has already seen exponential growth in a wide range of use-cases across numerous application domains. As academics around the world continue to examine its capabilities, there is widespread consensus that in order to get the most out of this technology and fully realise its potential, IoT must be built on a flexible network architecture with strong support for security, privacy, and trust. Blockchain (BC) technology, on the other hand, has lately emerged as a breakthrough technology with the promise to give several beneficial qualities such as robustness, support for integrity, anonymity, decentralisation, and autonomous control. Several BC systems are offered, which may be appropriate for various use-cases, including IoT applications. As a result, the integration of IoT with BC technology is seen as a potential solution to some critical concerns. To do this, a good grasp of the requirements of various IoT applications and the viability of a BC platform for a specific application satisfying its underlying requirements is required. This project explains many ways such as the gateway process and sensor device. By addressing the present blockchain concerns, IoT may enable a variety of security services, all of which are described in detail. Various authors present some common facts on the use of blockchain in IoT, which aids in a thorough understanding of the concept. Blockchain improves security and privacy in IoT platforms. In this project, an extra immutable ledger is created using all of the resources and information mentioned in the existing procedure. [1].

Research on the application and examination of electronic evidence preserved on the blockchain in Chinese copyright judicial practice

In the era of smart justice, blockchain technology has revolutionized the way of preserving and examining electronic evidence.Blockchain technology has its functional advantages of distributed storage, hash function verification, and timestamp and accordingly possesses the technical characteristics of stability, integrity, and immutability. As such, blockchain technology can help alleviate the dilemma over electronic evidence due to its flaws, such as easy distortion and modification and difficulty in the collection, especially in the cases of copyright disputes where it is difficult to determine the ownership of works and fixation of evidence. The paper explores two ways of applying blockchain evidence and their distinct proving roles in copyright infringement cases. The paper further finds the similarities and differences between the two types of blockchain electronic preservation in the judicial review mechanism. In Chinese copyright judicial practice, the ambiguity in the rules of blockchain evidence, the inconsistency of different courts in examining blockchain evidence, and the disarray of blockchain evidence preservation platforms all confused and affected judicial discretion when dealing with blockchain evidence. Learning from the United States, the paper concludes with standard-related, judicial, and self-governance suggestions to pave the way for applying and examining blockchain evidence in Chinese copyright judicial practice.

Semantic Web and blockchain technologies: Convergence, challenges and research trends

In recent years, on the one hand, we have witnessed the rise of blockchain technology, which has led to better transparency, traceability, and therefore, trustworthy exchange of digital assets among different actors. On the other hand, achieving trustworthy content exchange has been one of the primary objectives of the Semantic Web, part of the World Wide Web Consortium. Semantic Web and blockchain technologies are the fundamental building blocks of Web3 (the third version of the Internet), which aims to link data through a decentralized approach. Blockchain provides a decentralized and secure framework for users to safeguard their data and take control over their data and Web3 experiences. However, developing trustworthy decentralized applications (Dapps) is a challenge because many blockchain-based functionalities must be developed from scratch, and combined with data semantics to open new innovative opportunities. In this survey paper, we explore the cross-cutting domain of the Semantic Web and blockchain and identify the critical building blocks required to achieve trust in the Next-Generation Internet. The application domains that could benefit from these technologies are also investigated. We developed a deep analysis of the published literature between 2015 and 2023. We performed our analysis in different digital libraries (e.g., Elsevier, IEEE, ACM), and as a result of our research, we retrieved 137 papers, of which 97 were retrieved as relevant to include in the paper. Furthermore, we studied several aspects (e.g., network type, transactions per second) of existing blockchain platforms. Semantic Web and blockchain technologies can be used to realize a verification and certification process for data quality. Examples of mechanisms to achieve this are the Decentralized Identities of the Semantic Web or the various blockchain consensus protocols that help achieve decentralization and realize democratic principles. Therefore, Semantic Web and blockchain technologies should be combined to achieve trust in the highly decentralized, semantically complex, and dynamic environments needed to build smart applications of the future.

A decision-making framework for blockchain platform evaluation in spherical fuzzy environment

Blockchain systems with critical features (e.g., security, flexibility against attacks, and data traceability) have created possibilities for users to develop innovative economic and business models. Despite the abundance and variety of features of blockchain technology, choosing a suitable and reliable blockchain platform is somewhat challenging. Several criteria, including profitability, sustainability, and popularity, should be considered to identify such platforms. Accordingly, this study investigates the blockchain platform evaluation and selection as a multi-criteria decision-making (MCDM) problem. In this regard, we propose an integrated approach based on the extended version of MCDM methods in a spherical fuzzy environment. In the developed approach, the main criteria are weighted using the developed spherical fuzzy best-worst method (SF-BWM) to reduce uncertainty in pairwise comparisons. Then, the 15 blockchain platforms are analyzed and ranked using spherical fuzzy measurement of alternatives and ranking according to the compromise solution (SF-MARCOS). The outputs of this study imply that Bitcoin and Ethereum are placed in the first and second priorities, respectively. The comparison of the results with other MCDM methods and sensitivity analysis demonstrates the performance of the proposed approach and its ranking stability in various scenarios.

Decentralized Voting System Using Blockchain Technology

Blockchain verifies security using a distributed mechanism. For several new and developing products and services, blockchain technology is touted as a game-changer. Providing a distributed architecture to manage and sustain an open voting system would be the aim of such a plan. A system called blockchain stores data in a way that makes it difficult or almost impossible to make changes to it. The sharing economy may be benefited by a very wide variety of applications made possible by blockchain technology. That will be used to quantify how blockchain technology may be used to facilitate distributed electronic voting. The suggested solution implements a voting mechanism using the Aadhar API on an Ethereum network on a blockchain platform. Electronic voting is expected to promote openness, and voters are required to lessen dishonesty and irregularities in the voting procedures. Voters will be able to cast their ballots from home by using this technology. The technology seeks to improve voting process transparency and strengthen fraud prevention by supplanting the conventional pen and paper method. Key Words: Blockchain, Distributed General Ledger, Ethereum, Smart Contracts, P2P network, Consensus Algorithm, PoW Algorithm, Cryptography, Voter Privacy, Trustless Environment, Electrical integrity.

HPCchain: A Consortium Blockchain System Based on CPU-FPGA Hybrid-PUF for Industrial Internet of Things

Industrial Internet of Things (IIoT) is experiencing rapid developments in the era of Industry 4.0. However, the ever-increasing applications put forwards higher requirements for authentication. Facing such a problem, researchers combine two cutting-edge techniques, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.,</i> Physical Unclonable Function (PUF) and blockchain. In detail, PUF can generate multiple Challenge-Response Pairs (CRPs) for IIoT devices by leveraging their unique physical features. Moreover, blockchain platforms are employed for storing/synchronizing CRPs, thereby resisting the single-point-failure. Although realizing the unclonable authentications, the existing works ignore the device heterogeneity of IIoT and fail to develop the specified blockchain platform for supporting PUF. In this article, we present a Hybrid PUF-based consortium blockchain for IIoT authentication, named HPCchain. Specifically, we first present the notion of Hybrid-PUF, which assigns different devices to generate different types of PUFs, and then employs them to play different roles in HPCchain. In this way, we can overcome the IIoT heterogeneity. Moreover, we propose the PUF-empowered credit scheme for HPCchain and realize the dynamic endorsement, with which we develop a PUF-based consensus mechanism for HPCchain. Finally, we design the registration and authentication schemes for IIoT nodes, atop HPCchain. Extensive experiments demonstrate the validity of our proposals.

Mapping user behaviors to identify professional accounts in Ethereum using semi-supervised learning

Ethereum is one of the largest blockchain platforms currently that has become a digital business environment. This platform allows for decentralized transactions between anonymous users. Thus, the development of methods to identify users’ behaviors and keep them anonymous can potentially leverage business on this platform. In this work, we aim to combine different categories of machine learning approaches, namely, unsupervised and semi-supervised, to map the behaviors of users’ owned accounts and identify users with professional activities in Ethereum. In addition, we provide here data to the community and analyze different machine learning techniques to characterize the users of Ethereum. These are challenging tasks due to the small fraction of publicly labeled data referring to users’ accounts that provide services on this platform, such as exchange, payment, and entertainment, among most casual behavior users. Initially, we use unsupervised learning techniques to cluster the unlabeled users’ accounts and to identify a set of them with casual behavior. As an outcome, a dataset containing labeled (casual or professional) and unlabeled instances is obtained. Semi-supervised learning methods are then applied (i) to generate models that classify accounts’ behaviors into casual or professional ones and (ii) to discover accounts with professional behaviors among the unlabeled ones. Computational experiments were conducted, and the results obtained by the proposed procedure are compared to those achieved by supervised learning techniques from the literature. The proposal outperformed those from the literature and reached values higher than 95% for the accuracy, precision, recall, Fβ-scores, MCC, and AUC-ROC.

Implementation of blockchain technology in the system of accounting and analytical support for the public sector

The study addressed the problem of developing a mechanism for introducing blockchain technology into the system of accounting and analytical support for public sector entities. In the course of the research, the volumes and types of financial violations by public sector entities were analyzed. Identified violations were committed by public sector entities, and their significant share fell on the system of accounting and analytical support, in particular, financial reporting, budget execution. Legal restrictions on the introduction of blockchain technology for public sector entities were outlined. The absence of a number of acts in the field of digitization, protection of state secrets, cyber security, international standards, etc. in the legal field was established. The characteristics and mechanisms of blockchain technology were described, the types of blockchains based on permission models (open, closed) were defined. The technological characteristics of the use of blockchain platforms in the system of accounting and analytical support of public sector entities have been determined. The need to use blockchain applications such as smart contracts was indicated. It is noted that the use of smart contracts can be developed on blockchain platforms such as Ethereum, NXT, and Hyperledger; their key characteristics were described. A comparative description of transactions of state funds in the traditional accounting system and with the use of blockchain systems is given. The problem of the materiality of the transaction cost when transferring large volumes of data was outlined using the Ethereum platform as an example; its shortcomings were identified. The development of a mechanism for introducing blockchain technology into the system of accounting and analytical support using the Hyperledger platform, which has an open-source community focused on the development of a set of stable frameworks, tools, and libraries for deploying enterprise-level blockchains, was described. The advantages and disadvantages of introducing blockchain technology into the system of accounting and analytical support have been determined.

Smart contracts and business process automation: the technical aspect

Purpose. To analyze the process of implementing smart contracts for the automation of business processes, aimed at achieving high reliability and cybersecurity during contract execution, optimizing transaction costs, and maximizing the productivity of the enterprise’s internal operations. Methodology. The research results were obtained using special and general methods of scientific knowledge, namely descriptive, comparative, strategic analysis, abstract-logical and generalization. Findings. The study revealed the potential of smart contracts based on blockchain technology to improve business process efficiency, reduce costs, and ensure innovative development in the Ukrainian business environment. Originality. A comprehensive analysis of the technical aspects of using smart contracts based on blockchain technology to automate business processes has been conducted; their impact on the business environment has been assessed; a comparison of popular programming languages and blockchain platforms for the development and deployment of smart contracts has been made; a SWOT-analysis of the implementation of smart contracts at Ukrainian enterprises has been carried out, which opens up prospects for innovative approaches to business practices and their optimization. Practical value. The results of the study can be used to develop and implement innovative strategies in a business environment based on the integration of smart contracts based on blockchain technology in order to improve the efficiency of business processes.

Performance analysis of LogisticChain: A blockchain platform for maritime logistics

The application of blockchain and smart contracts has been widely acknowledged as essential in digitised logistics, offering improved traceability, transparency, and efficiency. However, concerns regarding performance and implementation limitations persist. To demonstrate the challenges regarding the performance and efficiency of blockchain in logistics use cases, this study presents a proof-of-concept model by leveraging the Hyperledger Fabric blockchain network to emulate the shipping logistics process and illustrate the automated and self-executing nature of smart contracts and transactions among various logistics participants by implementing RAFT consensus mechanism. Utilizing Hyperledger Caliper, this study evaluates the performance by systematically adjusting parameters including the number of clients, the number of concurrent transactions, and transaction rates per second. Then nuanced variations in latency, send rate, and throughput are examined. Preliminary findings indicate significant performance impacts related to client numbers and transaction rates per second. When exceeding the processing capacity, the average latency of transactions experiences an exponential increase due to limited resources. Furthermore, different types of operations are compared, with Read operations exhibiting the lowest latency and Update operations displaying the highest latency due to the complex computations and validations involved. Lastly, the latency measures of the LogisticChain network between fixed-rate and linear-rate controllers are compared, highlighting lower latency with fixed-rate controllers. This research contributes to the advancement of knowledge in this field by developing open-source codes specifically tailored for maritime logistics use cases.

Health Block: A Blockchain Based Secure Healthcare Data Storage and Retrieval System for Cloud Computing

Data in healthcare domain is highly sensitive in nature. Besides, there is need for maintaining integrity of such data. Blockchain technology has emerged to solve the problem of data integrity and non-repudiation with immutable storage in distributed repository. Thus secure data storage and retrieval in cloud environments is made possible using blockchain implementation. There are many existing healthcare systems with blockchain integration found in the literature. However, there is need for a system that supports complete set of operations that are governed by smart contracts. Another important consideration is that end users should be able to operate healthcare system without the need for knowledge of blockchain technology. Towards this end, in this paper, we proposed a Blockchain based secure healthcare data storage and retrieval system known as HealthBlock for cloud computing environments. We defined smart contract with underlying structures and functions using Solidity language for Ethereum blockchain platform. We also proposed and implemented an algorithm known as Healthcare Transactions over Blockchain (HToB). This algorithm supports secure blockchain based data storage and retrieval governed by smart contracts. Our system is evaluated using user-friendly web based client application. The experimental results showed that our system is able to ensure data integrity and non-repudiation besides reaping all benefits of blockchain technology.