It has been a decade since the concept of blockchain was invented as the underlying core data structure of the permissionless or public Bitcoin cryptocurrency network. Since then, several cryptocurrencies, tokens and ICOs have emerged. After much speculation and hype, significant number of them have become problematic or worthless! The public blockchain system Ethereum emerged by generalizing the use of blockchains to manage any kind of asset, be it physical or purely digital, with the introduction of Smart Contracts. Over the years, numerous myths have developed with respect to the purported utility and the need for public blockchains. The adoption and further adaptation of blockchains and smart contracts for use in the permissioned or private environments is what I consider to be useful and of practical consequence. Hence, the technical aspects of only private blockchain systems will be the focus of my SIGMOD 2019 keynote. Along the way, I will bust many myths associated with public blockchains. I will also compare traditional database technologies with blockchain systems' features and identify desirable future research topics.
Min Choi, Rupali Shinde, Sechang Oh, OhâYoung Kwon
In this paper, we present a badge awarding system for performance assessment in education using blockchain technology. Learners will be awarded badges, which are certified for a predetermined level of progress in terms of learning. All the badges are stored in a backpack, which is an environment for storing and presenting the obtained badges. Badges are immutable and verifiable as well as rigid. The use of badges in the education system makes education more interesting, skill-based, and adaptable to changes. The key contribution of our work is in terms of compatibility with Openbadge specification and integrated cooperating platform between digital badge awarding and blockchaining. Our system implementation is compatible with Open Badges of IMS Global Learning Consortium, which is used to earn, issue, and award badges across various platforms. The badges are trusted by the IMS standard, the criteria to earn a badge is verified through the network, and the overall process is transparent compared to the traditional education system. Moreover, all badge awarding events in our system are recorded in a blockchain. Once stored, the contents cannot be tampered with. Thereafter, anyone can check the validity of the badge through the blockchain. Our platform will be useful for distance learning as well as time and location independent learning. The experimental results are as follows. On a Bitcoin-based digital badge publishing platform, the execution time required to award the badge is 24.53 s, while on the Ethereum-based digital badge publishing platform, the execution time to award the badge is only 3.86 s. It can also be used for career management and personal history. The learners can obtain the current knowledge required for a job. Lifelong learning will be also possible with this platform.
Cloud storage enables users to outsource data to storage servers and retrieve target data efficiently. Some of the outsourced data are very sensitive and should be prevented for any leakage. Generally, if users conventionally encrypt the data, searching is impeded. Public-key encryption with keyword search (PEKS) resolves this tension. Whereas, it is vulnerable to keyword guessing attacks (KGA), since keywords are low-entropy. In this paper, we present a secure PEKS scheme called SEPSE against KGA, where users encrypt keywords with the aid of dedicated key servers via a threshold and oblivious way. SEPSE supports key renewal to periodically replace an existing key with a new one on each key server to thwart the key compromise. Furthermore, SEPSE can efficiently resist online KGA, where each keyword request made by a user is integrated into a transaction on a public blockchain (e.g., Ethereum), which allows key servers to learn the number of keyword requests made by the user without requiring a synchronization between them for per-user rate limiting. Security analysis and performance evaluation demonstrate that SEPSE provides a stronger security guarantee compared with existing schemes, at the expense of acceptable computational costs.
Proof-of-Storage (PoS) is a collective term for protocols that allow proving data integrity and availability. There exist several PoS schemes. While they differ in detailed specifications, their common primary advantage is eliminating the need for trust between storage providers and data owners. However, there does not exist a mechanism to provide self-emerging delivery of requests for proof of storage, commonly known as challenges.\n\nThis paper presents a decentralized system for PoS using self-emerging challenges built on smart contract in the Ethereum platform. Self-emerging challenges provide an automated mechanism for ensuring integrity and persistence of data at chosen time intervals. The design employs participating nodes in the Ethereum blockchain, commonly referred to as peers, to store and route challenges to storage providers. The peers are compensated for their service by their respective employers. Data owners are enabled to schedule the time of emergence of a challenge to storage providers. Upon a received challenge, storage providers prove the integrity and persistence of data by responding correctly to the challenge. The design builds on the existing work of decentralized self-emerging data systems over Ethereum blockchain networks. We show that this work can be utilized for PoS and solve the problems that the incorporation and adaptation of this work raises.\n\nWe evaluate the proposed system based on several factors. We investigate the security of the system based on the different attacks that the participants may execute for exploitation. Moreover, we evaluate the attractiveness of participating in the system based on the gained remuneration by peers and the positive reputation gained by storage providers for proving the integrity of their clientsâ data. We also evaluate the expenses of data owners utilizing the proposed system based on the inherited costs of invoking smart contract functions in the Ethereum platform. Lastly, through analysis, we find that to minimize the total costs in the system, the number of employed peers should be restricted to one in each path. In other words, one peer to deliver a PoS challenge to the storage service provider. We show that this additionally improves the fairness of remuneration payout to peers and analyze how security is affected by always utilizing one peer in each path. We discover that this improves prevention against drop attacks, while it to some degree decreases the prevention of release-ahead attacks which we deem less critical. Through these analyses, we recognize that the benefits greatly outweigh the drawback, and we make a suggestion that data owners should select exactly one peer per path in their services.
Fangyu Gai, Cesar Grajales, Jianyu Niu, Jalalzai, Mohammad Mussadiq ¡ 5 authors
Sidechain technology has been envisioned as a promising solution to accelerate today's public blockchains in terms of scalability and interoperability. By relying on the mainchain for security, different sidechains can formulate their own rules to reach consensus. Although the literature has considered the possibility of using consensus protocols in the sidechain, so far a tailor-made consensus protocol for sidechains with high performance and formal security proof has not been attempted. To fill this gap, we introduce Cumulus, a low overhead, highly efficient, security provable sidechain protocol. Cumulus makes use of smart contracts to ensure that only one block proposed in the sidechain will be enforced on the mainchain in each round, thereby achieving consensus in an efficient manner. We give a formal specification of Cumulus which ensures safety and liveness without any online requirements of clients. For security analysis, we provide formal security definitions and proofs under Universally Composable Security (UCS) model. As a proof of concept, we implement Cumulus and evaluate it in an Ethereum testnet.
The emergence of e-commerce and e-voting platforms has resulted in the rise in the volume of sensitive information over the Internet. This has resulted in an increased demand for secure and private means of information computation. Towards this, the Yao's Millionaires' problem, i.e., to determine the richer among two millionaires' securely, finds an application. In this work, we present a new solution to the Yao's Millionaires' problem namely, Privacy Preserving Comparison (PPC). We show that PPC achieves this comparison in constant time as well as in one execution. PPC uses semi-honest third parties for the comparison who do not learn any information about the values. Further, we show that PPC is collusion-resistance. To demonstrate the significance of PPC, we present a secure, approximate single-minded combinatorial auction, which we call TPACAS, i.e., Truthful, Privacy-preserving Approximate Combinatorial Auction for Single-minded bidders. We show that TPACAS, unlike previous works, preserves the following privacies relevant to an auction: agent privacy, the identities of the losing bidders must not be revealed to any other agent except the auctioneer (AU), bid privacy, the bid values must be hidden from the other agents as well as the AU and bid-topology privacy, the items for which the agents are bidding must be hidden from the other agents as well as the AU. We demonstrate the practicality of TPACAS through simulations. Lastly, we also look at TPACAS' implementation over a publicly distributed ledger, such as the Ethereum blockchain.
Franco Valencia, Alfonso GĂłmez-Espinosa, BenjamĂn ValdĂŠs-Aguirre
Cryptocurrencies are becoming increasingly relevant in the financial world and can be considered as an emerging market. The low barrier of entry and high data availability of the cryptocurrency market makes it an excellent subject of study, from which it is possible to derive insights into the behavior of markets through the application of sentiment analysis and machine learning techniques for the challenging task of stock market prediction. While there have been some previous studies, most of them have focused exclusively on the behavior of Bitcoin. In this paper, we propose the usage of common machine learning tools and available social media data for predicting the price movement of the Bitcoin, Ethereum, Ripple and Litecoin cryptocurrency market movements. We compare the utilization of neural networks (NN), support vector machines (SVM) and random forest (RF) while using elements from Twitter and market data as input features. The results show that it is possible to predict cryptocurrency markets using machine learning and sentiment analysis, where Twitter data by itself could be used to predict certain cryptocurrencies and that NN outperform the other models.
With the prevalence of blockchain, more and more Decentralized Applications (DApps) are deployed on Ethereum to achieve the goal of communicating without supervision. Users habits may be leaked while these applications adopt SSL/TLS to encrypt their transmission data. Encrypted protocol and the same blockchain platform bring challenges to the traffic classification of DApps. Existing encrypted traffic classification methods suffer from low accuracy in the situation of DApps.
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
Imtiaz Sifat, Azhar Mohamad, Mohammad Syazwan Bin Mohamed Shariff
This paper investigates lead-lag relationship between heavyweight cryptocurrencies Bitcoin and Ethereum. Traditional studies of information flow between markets preponderate on cash vs. futures, whereby researchers are interested in the stabilizing impact of futures on spot markets. While interest in the same relationship in the nascent cryptocurrency sphere is emerging, little is known regarding price leadership between these assets. In this paper, we employ a battery of statistical testsâVECM, Granger Causality , ARMA, ARDL and Wavelet Coherenceâto identify price leadership between the two crypto heavyweights Bitcoin and Ethereum. Based on one year hourly and daily data from August 2017 through to September 2018, our tests yield varied results but largely suggest bi-directional causality between the two assets. Moreover, the results indicate that intraday crypto traders can barely exploit Bitcoin-Ethereum hourly or daily price discovery process to their advantage.
Josep LluĂs Ferrer Gomila, M. Francisca Hinarejos, Andreu Pere Isern-DeyĂ
Electronically signing contracts is fundamental for e-commerce transactions. The main property that contract signing protocols must achieve is fairness of the exchange. The solutions presented to date are divided into two major types: those that have a trusted third party (TTP) to achieve fairness and those that do not. In the literature, we find more than 40 published proposals, but none of these proposed protocols has become a recognized or de facto standard in the market. Blockchain has provided a new way to address classic problems such as double spending, as well as problems such as fairness. In this article, we present a protocol for contract signing based on blockchain. Our proposed protocol does not require a conventional TTP, and it does not present the disadvantages of solutions without a TTP (computational and/or communication cost). The protocol satisfies the necessary security requirements: fairness, timeliness and non-repudiation. We demonstrate the feasibility of the protocol with a cost analysis and a proof of concept implementation. In addition, we show how Ethereum can be integrated in our solution as an alternative platform to the use of Bitcoin. Finally, we show how our proposal improves previous solutions for contract signing based on blockchain in terms of cost, efficiency and security.
BlaĹž Podgorelec, Patrik Rek, Miha Strehar, Muhamed TurkanoviÄ
Advanced Information Technology and Services: OTS 2019: Proceedings of the Twenty-fourth Conference, 18th - 19th of June, 2019. The papers in the proceedings of the 24th Professional Conference on Advanced Information Technology and Services address the extremely topical challenges that we (IS/IT experts, Software Engineers, Computer Scientists, Data Scientists, software and solution architects, developers, IT managers, etc.) encounter in our daily work. The authors present the innovative solutions and rich experience gained by conducting real-life projects: Applying Augmented Intelligence and Machine Learning technologies, Using Blockchain technologies and platforms, Developing loosely coupled micro-services, Providing full virtualization and exploitation of distributed infrastructures, Ensuring cybersecurity, confidentiality and privacy, Applying large-scale agile methods in distributed teams, Introducing agile approaches that enable the rapid and efficient software development via automated processes, and continuous testing, integration, delivery & deployment Updating and upgrading existing Information Systems, Incorporating advanced programming languages and development environments, Developing user-friendly web and mobile solutions & services.
Information transfer between time series is calculated using the asymmetric information-theoretic measure known as transfer entropy. Gewekeâs autoregressive formulation of Granger causality is used to compute linear transfer entropy, and Schreiberâs general, non-parametric, information-theoretic formulation is used to quantify nonlinear transfer entropy. We first validate these measures against synthetic data. Then we apply these measures to detect statistical causality between social sentiment changes and cryptocurrency returns. We validate results by performing permutation tests by shuffling the time series, and calculate the Z -score. We also investigate different approaches for partitioning in non-parametric density estimation which can improve the significance. Using these techniques on sentiment and price data over a 48-month period to August 2018, for four major cryptocurrencies, namely bitcoin (BTC), ripple (XRP), litecoin (LTC) and ethereum (ETH), we detect significant information transfer, on hourly timescales, with greater net information transfer from sentiment to price for XRP and LTC, and instead from price to sentiment for BTC and ETH. We report the scale of nonlinear statistical causality to be an order of magnitude larger than the linear case.
Ethereum smart contracts are public, immutable and distributed and, as such, they are prone to vulnerabilities sourcing from programming mistakes of developers. This paper presents SAFEVM, a verification tool for Ethereum smart contracts that makes use of state-of-the-art verification engines for C programs. SAFEVM takes as input an Ethereum smart contract (provided either in Solidity source code, or in compiled EVM bytecode), optionally with assert and require verification annotations, and produces in the output a report with the verification results. Besides general safety annotations, SAFEVM handles the verification of array accesses: it automatically generates SV-COMP verification assertions such that C verification engines can prove safety of array accesses. Our experimental evaluation has been undertaken on all contracts pulled from etherscan.io (more than 24,000) by using as back-end verifiers CPAchecker, SeaHorn and VeryMax.
Daehwa Rayer Lee, Yunhee Jang, Hanbin Jang, Hyoungshick Kim
Recently, Samsung released Galaxy S10 supporting the cryptowallet feature [5]. However, it is still questionable whether cryptocurrency can be popularly used for mobile payments because processing transactions in existing blockchain systems are too slow. For example, public blockchain systems such as Bitcoin [6] (7 transactions per second (TPS)) and Ethereum (15 TPS) are significantly slower than mainstream payment systems such as Visa (2,000 TPS) using a centralized database.
Blockchain Technology Applications and Security
IoT and Edge/Fog Computing
Advanced Steganography and Watermarking Techniques
A Coordination Blockchain is a blockchain with the task of coordinating activities of multiple private blockchains. This paper discusses the pros and cons of using Ethereum MainNet, the public Ethereum blockchain, as a Coordination Blockchain. The requirements Ethereum MainNet needs to fulfil to perform this role are discussed within the context of Ethereum Private Sidechains, a private blockchain technology which allows many blockchains to be operated in parallel, and allows atomic crosschain transactions to execute across blockchains. Ethereum MainNet is a permissionless network which aims to offer strong authenticity, integrity, and non-repudiation properties, that incentivises good behaviour using crypto economics. This paper demonstrates that Ethereum MainNet does deliver these properties. It then provides a comprehensive review of the features of Ethereum Private Sidechains, with a focus on the potential usage of Coordination Blockchains for these features. Finally, the merits of using Ethereum MainNet as a Coordination Blockchain are assessed. For Ethereum Private Sidechains, we found that Ethereum MainNet is best suited to storing long term static data that needs to be widely available, such as the Ethereum Registration Authority information. However, due to Ethereum MainNet's probabilistic finality, it is not well suited to information that needs to be available and acted upon immediately, such as the Sidechain Public Keys and Atomic Crosschain Transaction state information that need to be accessible prior to the first atomic crosschain transaction being issued on a sidechain. Although this paper examined the use of Ethereum MainNet as a Coordination Blockchain within reference to Ethereum Private Sidechains, the discussions and observations of the typical tasks a Coordination blockchain may be expected to perform are applicable more widely to any multi-blockchain system.
Ten years have passed since the emergence of Bitcoin and with it cryptocur- rencies as a new class of assets. Now, cryptocurrencies are not uncommon tool of investment and subject of academic research. This thesis focuses on investigating possible presence of weekly and monthly seasonal patterns in cryptocurrencies, namely Bitcoin, Litecoin, Ripple, Monero, Dash, Stellar and partly Ethereum, which are selected as representative sample. Insuffi- cient evidence is found for the day-of-the-week effect, the January effect is however revealed as significant by different methods in the whole sample, with cryptocurrencies generally exhibiting higher returns towards the end of the year and lowest from January to March. Examining probable causes of revealed seasonality, it is found that these are not likely to be caused by peculiar price development in 2017 and 2018, as well as the Chinese New Year or brought to the market by proposed price drivers of Bitcoin. How- ever, significant evidence for correlation of patterns followed by Bitcoin and other examined cryptocurrencies is found.
A Coordination Blockchain is a blockchain with the task of coordinating\nactivities of multiple private blockchains. This paper discusses the pros and\ncons of using Ethereum MainNet, the public Ethereum blockchain, as a\nCoordination Blockchain. The requirements Ethereum MainNet needs to fulfil to\nperform this role are discussed within the context of Ethereum Private\nSidechains, a private blockchain technology which allows many blockchains to be\noperated in parallel, and allows atomic crosschain transactions to execute\nacross blockchains. Ethereum MainNet is a permissionless network which aims to\noffer strong authenticity, integrity, and non-repudiation properties, that\nincentivises good behaviour using crypto economics. This paper demonstrates\nthat Ethereum MainNet does deliver these properties. It then provides a\ncomprehensive review of the features of Ethereum Private Sidechains, with a\nfocus on the potential usage of Coordination Blockchains for these features.\nFinally, the merits of using Ethereum MainNet as a Coordination Blockchain are\nassessed. For Ethereum Private Sidechains, we found that Ethereum MainNet is\nbest suited to storing long term static data that needs to be widely available,\nsuch as the Ethereum Registration Authority information. However, due to\nEthereum MainNet's probabilistic finality, it is not well suited to information\nthat needs to be available and acted upon immediately, such as the Sidechain\nPublic Keys and Atomic Crosschain Transaction state information that need to be\naccessible prior to the first atomic crosschain transaction being issued on a\nsidechain. Although this paper examined the use of Ethereum MainNet as a\nCoordination Blockchain within reference to Ethereum Private Sidechains, the\ndiscussions and observations of the typical tasks a Coordination blockchain may\nbe expected to perform are applicable more widely to any multi-blockchain\nsystem.\n
Those working on Blockchain technologies have described several new innovative directions and novel services in the Internet of things (IoT), including decentralized trust, trusted and verifiable execution of smart contracts, and machine-to-machine communications and automation that reach beyond the mere exchange of data. However, applying blockchain principles in the IoT is a challenge due to the constraints of the end devices. Because of fierce cost pressure, the hardware resources in these devices are usually reduced to the minimum necessary for operation. To achieve the high coverage needed, low bitrate mobile or wireless technologies are frequently applied, so the communication is often constrained, too. These constraints make the implementation of blockchain nodes for IoT as standalone end-devices impractical or even impossible. We therefore investigated possible design approaches to decentralized applications based on the Ethereum blockchain for the IoT. We proposed and evaluated three application architectures differing in communication, computation, storage, and security requirements. In a pilot setup we measured and analyzed the data traffic needed to run the blockchain clients and their applications. We found out that with the appropriate designs and the remote server architecture we can strongly reduce the storage and communication requirements imposed on devices, with predictable security implications. Periodic device traffic is reduced to 2400 B/s (HTTP) and 170 B/s (Websocket) from about 18 kB/s in the standalone-device full client architecture. A notification about a captured blockchain event and the corresponding verification resulted in about 2000 B of data. A transaction sent from the application to the client resulted in an about 500 B (HTTP) and 300 B message (Websocket). The key store location, which affects the serialization of a transaction, only had a small influence on the transaction-related data. Raw transaction messages were 45 B larger than when passing the JSON transaction objects. These findings provide directions for fog/cloud IoT application designers to avoid unrealistic expectations imposed upon their IoT devices and blockchain technologies, and enable them to select the appropriate system design according to the intended use case and system constraints. However, for very low bit-rate communication networks, new communication protocols for device to blockchain-client need to be considered.
Abstract This chapter provides an overview of how US securities regulation applies to the sale of cryptographic tokens using a distributed ledger, so-called initial coin offerings. Token sale transactions that meet the definition of âinvestment contractâ qualify as regulated securities transactions following the seminal 1946 court decision in the Securities Exchange Commissionâs lawsuit against the W. J. Howey company. Currently, there exists substantial legal uncertainty regarding the regulatory classification of token sales involving utility tokens that provide their holders with non-financial, software-based functionality. As implied in a June 2018 speech by a high-ranking SEC official, sales of tokens may initially qualify as regulated securities transactions, yet later fail to qualify as regulated investment contracts if the tokensâ underlying network becomes sufficiently decentralized. Distributed ledger technology is disrupting the nature and operation of early-stage fundraising and access to software services and enabling the sale of digital tokens that operate as a cryptocurrency or provide access to a software service through the use of a blockchain or distributed ledger. The sale of such tokens, so-called initial coin offerings (âICOsâ), is often in exchange for cryptocurrencies, such as Ethereum or Bitcoin (however, tokens could be sold in exchange for fiat currency). From January to May 2018, globally US$13.7 billion in tokens were sold by 537 companies or projects, an amount greater than all previous time periods combined. This chapter discusses under what circumstances US securities law applies to the sale of such tokens.
Abstract Cryptocurrencies such as Bitcoin or Ethereum are gaining ground not only as alternative modes of payment but also as platforms for financial innovation, particularly through token sales or initial coin offerings (âICOsâ). All of these ventures are based on decentralized, permissionless blockchain technology, distinguished by their openness to, and the formal equality of, participants. However, recent cryptocurrency crises have shown that these architectures lack robust governance frameworks and are therefore prone to patterns of re-centralization. They are informally dominated by coalitions of powerful players within the cryptocurrency ecosystem who may violate basic rules of the blockchain community without accountability or sanction. This chapter first suggests that cryptocurrency and token-based ecosystems can be fruitfully analysed as complex systems that have been studied for decades in complexity theory and have recently gained prominence in financial regulation, too. It applies these insights to three key case studies: the Bitcoin Hard Fork of 2013; the Ethereum hard fork of 2016, following the DAO hack; and the ongoing Bitcoin scaling debate. Second, the chapter argues that complexity-induced uncertainty can be reduced, and elements of stability and order strengthened, by adapting a corporate governance framework to blockchain-based organizations: cryptocurrencies, and decentralized applications built on top of them via token sales. The resulting âcomply-or-explainâ approach combines transparency and accountability with the necessary flexibility that allows blockchain developers to continue to experiment for the sake of innovation. Eventually, however, the coordination of these activities may necessitate the establishment of a self-regulatory institution.
PeerCash is an decentralized application built on Ethereum blockchain technology. Decentralization means that there is no concept of having admin. Blockchain is a decentralized, distributed ledger secured technology which is immutable and verifiable. Every events in blockchain is recorded on blocks and it is encrypted using cryptography hashing. The advantage of PeerCash is that we can completely avoid the middle man from the web shopping payment system. That is we can completely remove the bank from interfering with our payment system and the buyer and seller can directly proceed their transaction and make their purchase. PeerCash transactions is completely recorded on blocks and the transactions is secured. So we can call PeerCash as a cryptocurrency. This paper describes about this application.
The blockchain was introduced as the core technology of the bitcoin concept of Satoshi Nakamoto in 2008. A blockchain is a technique to store, add and validate transaction data in an open computer network by cryptographic techniques in such a way that the correctness, immutability and safety of the data is ensured by a decentralised consensus mechanism. In the bitcoin blockchain, nodes that validate blocks by solving the cryptographic task are called âminersâ. For an assessment of bitcoin from a Shariâah perspective, it is important to distinguish the coin âbitcoinâ from the underlying blockchain or Distributed Ledger Technology. The Ethereum blockchain with Ether as its own token can be considered as a kind of operating system for a wide range of decentralised applications. Developments in the field of blockchains, cryptocurrencies, smart contracts and intelligent agents have attracted the attention of practitioners and proponents of Islamic finance as well as Shariâah scholars.
Blockchain-related discussions have become increasingly prevalent in programming Q&A websites, such as Stack Overflow and other Stack Exchange communities. Analyzing and understanding those discussions could provide insights about the topics of interest to practitioners, and help the software development and research communities better understand the needs and challenges facing developers as they work in this new domain. Prior studies propose the use of LDA to study the Stack Exchange discussions. However, a simplistic use of LDA would capture the topics in discussions blindly without keeping in mind the variety of the dataset and domain-specific concepts. Specifically, LDA is biased towards larger sized corpora; and LDA-derived topics are not linked to higher level domain-specific concepts. We propose an approach that combines balanced LDA (which ensures that the topics are balanced across a domain) with the reference architecture of a domain to capture and compare the popularity and impact of discussion topics across the Stack Exchange communities. Popularity measures the distribution of interest in discussions, and impact gauges the trend of popularity over time. We made a number of interesting observations, including: (1) Bitcoin, Ethereum, Hyperledger Fabric and Corda are the four most commonly-discussed blockchain platforms on the Stack Exchange communities. (2) A broad range of topics are discussed across the various platforms of distinct layers in our derived reference architecture. (3) The Application layer topics exhibit the highest popularity (33.2 percent) and fastest growth in topic impact since November 2015. (4) The Application, API, Consensus and Network layer topics are discussed across the studied blockchain platforms, but exhibit different distributions in popularity. (5) The impact of architectural layer topics exhibits an upward trend, but is growing at different speeds across the studied blockchain platforms. The breakdown of the topic impact across the architectural layers is relatively stable over time except for the Hyperledger Fabric platform. Based on our findings, we highlighted future directions and provided recommendations for practitioners and researchers.