By 2022, a change in the form of government from unitary to federal will likely happen in the Philippines, a nation of 104 million. Although decentralization is not new to the country owing to the passage of the Local Government Code of 1991, the transition will have major policy implications on the assignment of expenditure and revenue (taxation) responsibilities for government functions. This study focuses on the technical and vocational education and training (TVET), an important component of the Philippine Government’s national strategy for economic development and poverty alleviation. TVET governance in the Philippines is placed under the authority of the Technical Education and Skills Development Authority (TESDA), an agency attached to the national government which operates a network of over a hundred TVET training schools and institutes. With the impending shift to a federal system, TESDA needs to formulate a decentralization strategy, determining which sub-functions of TVET governance should be retained at the national level, devolved/transferred to subnational governments, and shared between the two levels government. This paper maintains that in addressing these policy issues, the Philippine Government should be guided by the principles of fiscal federalism and informed by existing TVET vi decentralization models in federal countries worldwide. This paper utilizes comparative institutional analysis, an analytical framework that examines existing institutional arrangements in some jurisdictions to inform policy formulation elsewhere. TVET governance in eight federal countries are analyzed by answering this question: Which sub-functions are assigned to what level of government? The sub-functions of the TVET system are: a) policy formulation and planning, b) standard-setting and regulatory, c) financing/contracting and d) provision of TVET services to clients. Based on the findings of the study, policy makers in the Philippines are enjoined to consider the following policy recommendations on decentralizing TVET under the proposed federal system: a. TVET policy formulation, planning, standard-setting and regulatory functions should be assigned solely to the national government so that TVET governance is harmonized across jurisdictions, and to be consistent with the national government’s equity goals; b. Financing/contracting for TVET can initially be assigned as a “shared function” between the national and subnational governments; however, in the long term, the subnational governments should develop their local revenue generation capacity and eventually be responsible for TVET financing/ contracting in their jurisdictions. Policy makers should also explore alternative models for TVET financing such as inclusion of TVET in the existing Special Education Fund (SEF) and establishing a TVET Training Fund; vii c. Provision of TVET training services can initially be a “shared function” between the two levels of government; however, as experiences of federal countries clearly show, the primary responsibility of providing TVET services to clients should rest with the subnational governments.
In the context of logistics, blockchain can help to increase end-to-end visibility along global supply chains. Thus, it can lead to improved tracking of goods and offer tamper-proof data to build trust among parties. Although a variety of blockchain use cases already exists, not all of them seem to rely on blockchain-specific features, but could rather be solved with traditional technologies. The purpose of this paper is, therefore, to identify characteristic use cases described for blockchain in the field of LSCM and to analyze them regarding their mindful technology use based on five mindful technology adoption principles: engagement with the technology; Technological novelty seeking; awareness of local context; cognizance of alternative technologies; and anticipation of technology alteration. The authors identified five blockchain case clusters and chose one case for each category to be analyzed in detail. Most cases demonstrate high engagement with the technology, but there are significant differences when it comes to the other mindful use principles. This paper highlights the need to understand the problem and to apply the right technology in order to solve it. When solving a problem, care should be taken to address a technology’s unique features to ensure effectiveness and cost-efficiency.
Lexi Brent, Anton Jurisevic, Michael Kong, Eric Liu · 8 authors
The rise of modern blockchains has facilitated the emergence of smart contracts: autonomous programs that live and run on the blockchain. Smart contracts have seen a rapid climb to prominence, with applications predicted in law, business, commerce, and governance. Smart contracts are commonly written in a high-level language such as Ethereum's Solidity, and translated to compact low-level bytecode for deployment on the blockchain. Once deployed, the bytecode is autonomously executed, usually by a %Turing-complete virtual machine. As with all programs, smart contracts can be highly vulnerable to malicious attacks due to deficient programming methodologies, languages, and toolchains, including buggy compilers. At the same time, smart contracts are also high-value targets, often commanding large amounts of cryptocurrency. Hence, developers and auditors need security frameworks capable of analysing low-level bytecode to detect potential security vulnerabilities. In this paper, we present Vandal: a security analysis framework for Ethereum smart contracts. Vandal consists of an analysis pipeline that converts low-level Ethereum Virtual Machine (EVM) bytecode to semantic logic relations. Users of the framework can express security analyses in a declarative fashion: a security analysis is expressed in a logic specification written in the \souffle language. We conduct a large-scale empirical study for a set of common smart contract security vulnerabilities, and show the effectiveness and efficiency of Vandal. Vandal is both fast and robust, successfully analysing over 95\% of all 141k unique contracts with an average runtime of 4.15 seconds; outperforming the current state of the art tools---Oyente, EthIR, Mythril, and Rattle---under equivalent conditions.
We study a stochastic game framework with dynamic set of players, for modeling and analyzing their computational investment strategies in distributed computing. Players obtain a certain reward for solving the problem or for providing their computational resources, while incur a certain cost based on the invested time and computational power. We first study a scenario where the reward is offered for solving the problem, such as in blockchain mining. We show that, in Markov perfect equilibrium, players with cost parameters exceeding a certain threshold, do not invest; while those with cost parameters less than this threshold, invest maximal power. Here, players need not know the system state. We then consider a scenario where the reward is offered for contributing to the computational power of a common central entity, such as in volunteer computing. Here, in Markov perfect equilibrium, only players with cost parameters in a relatively low range in a given state, invest. For the case where players are homogeneous, they invest proportionally to the 'reward to cost' ratio. For both the scenarios, we study the effects of players' arrival and departure rates on their utilities using simulations and provide additional insights.
We investigate connectedness within and across two major groups or assets: i) five popular cryptocurrencies, and ii) six major asset classes plus two commonly employed risk factors. Granger-causality tests uncover six direct channels of causality from the elements of the mainstream assets/risk factors group to digital assets. On the other hand there are two statistically significant causal links going in the other direction. In order to provide some perspective on the magnitude of the uncovered linkages we supplement the analysis by estimating networks from forecast error variance decompositions. The estimated connectedness within the groups is relatively large, whereas the linkages across the two groups are small in comparison. Namely, less than 2.2 percent of future uncertainty of any cryptocurrency is sourced from all non-crypto assets combined, while the joint contribution of all digital assets to non-crypto uncertainty does not exceed 1.5 percent.
Philipp Hacker, Ioannis Lianos, Georgios Dimitropoulos, Stefan Eich
This introductory chapter provides an overview of the main legal and policy implications of blockchain technology. It proceeds in four steps. First, the chapter traces the technical and legal evolution of blockchain applications since the early days of bitcoin, highlighting in particular the political ambitions and tensions that have marked many of these projects from the start. Second, it shows how blockchain applications have created new calculative spaces of financial markets that seek to challenge existing forms of money. Third, it discusses the core points of friction with incumbent legal systems, with a particular focus on the regulability of decentralized systems in general and data protection concerns in particular. Fourth, the chapter provides an outline to the contributions to the volume, which span a wide array of topics at the intersection of blockchain, law, and politics.
Kevin Eschen, Julianna Abel, Rachael Granberry, Brad Holschuh
Self-fitting is the ability of a wearable, garment or body-mounted object to recover the exact shape and size of the human body. Self-fitting is highly desirable for wearable applications, ranging from medical and recreational health monitoring to wearable robotics and haptic feedback, because it enables complex devices to achieve accurate body proximity, which is often required for functionality. While garments designed with compliant fabrics can easily accomplish accurate fit for a range of body shapes and sizes, integrated actuators and sensors require fabric stiffness to prevent drift and deflection from the body surface. This paper merges smart materials and structures research with anthropometric analysis and functional apparel methodologies to present a novel, functionally gradient self-fitting garment designed to address the challenge of achieving accurate individual and population fit. This fully functional garment, constructed with contractile SMA knitted actuator fabrics, exhibits tunable %-actuation contractions between 4-50%, exerts minimal on-body pressure (≤1333 Pa or 10 mmHg), and can be designed to actuate fully self-powered with body heat. The primary challenge in the development of the proposed garment is to design a functionally gradient system that does not exert significant pressure on part of the leg and/or remain oversized in others. Our research presents a new methodology for the design of contractile SMA knitted actuator garments, describes the manufacture of such self-fitting garments, and concludes with an experimental analysis of the garment performance evaluated through three-dimensional marker tracking.
Current electronic voting protocol require a centralized system to control the whole procedure from ballot inputs to result outputs and election monitoring. Meanwhile, blockchain technology provide a decentralized system which open across the whole network of untrusted participants. Applying blockchain technology into electronic voting protocol through a proper architecture can instil characteristic such as data confidentiality, data integrity and data authenticity. In this paper, we going to discuss a proposed method on how to leverage the advantages from blockchain into electronic voting protocol. This blockchain-based electronic voting protocol promise to provide a secure electronic election process given the proposed system works. We implement a protocol using blockchain to turn election protocol into an automated control system without relying any single point of entity. Lastly, we discuss the characteristics of our proposed blockchain-based electronic voting protocol in this paper. However, there are also emerging challenges and limitations awaiting to overcome. This paper gives a comprehensive overview of our proposed protocol.
Open access
Internet Traffic Analysis and Secure E-voting
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
This article deals with the concepts of social currencies and cryptocurrencies. The objective of the present paper is to identify similarities and differences between to two currency systems which represent a new generation of money that exists alongside the official and legal money system. The paper includes an analysis of the major characteristics of both currencies, their operating mechanisms in global and local contexts, as well as their risks and challenges for the financial markets. The article uses a mainly documentary research method and presents selected contributions of experts on the topics of social currencies and cryptocurrencies. Furthermore, empirical evidence is presented to highlight some important characteristics of the Bitcoin currency. The principal result of the paper is that, indeed there exist similarities between social currencies and cryptocurrencies, as for example the absence of a central bank, a lack of regulation and a limited minting process. However, because of aspects like their different origins, their local vs. global character and their inherent financial risks, the two money systems need to be interpreted as fundamentally different. Especially with reference to globally operating cryptocurrencies, given that there does not exist any public cover of the currency nor sufficient regulation, risk management mechanisms need to be improved in order to diminish the speculative tendencies inherent to this currency.
In this work, we propose an order book model with herd behavior. The proposed model is built upon two distinct approaches: a recent empirical study of the detailed order book records by Kanazawa et al. [Phys. Rev. Lett. 120, 138301] and financial herd behavior model. Combining these approaches allows us to propose a model that replicates the long-range memory of absolute returns and trading activity. We compare the statistical properties of the model against the empirical statistical properties of the Bitcoin exchange rates and New York stock exchange tickers. We also show that the fracture in the spectral density of the high-frequency absolute return time series might be related to the mechanism of convergence towards the equilibrium price.
Blockchain's vast applications in different industries have drawn several researchers to pursue extensive research in securing blockchain technologies. In recent times we could see several institutions coming together to create consortium based blockchain networks such as Hyperledger. Although for applications of blockchain such as Bitcoin, Litcoin, etc. the majority-attack might not be a great threat but for consortium based blockchain networks where we could see several institutions such as public, private, government, etc. are collaborating, the majority-attack might just prove to be a prevalent threat if collusion among these institutions takes place. This paper proposes a methodology where we can use intelligent software agents to monitor the activity of stakeholders in the blockchain networks to detect anomaly such as collusion, using supervised machine learning algorithm and algorithmic game theory and stop the majority attack from taking place.
Open access
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
The world of cryptocurrency is not transparent enough though it was established for innate transparent tracking of capital flows. The most contributing factor is the violation of securities laws and scam in Initial Coin Offering (ICO) which is used to raise capital through crowdfunding. There is a lack of proper regularization and appreciation from governments around the world which is a serious problem for the integrity of cryptocurrency market. We present a hypothetical case study of a new cryptocurrency to establish the transparency and equal right for every citizen to be part of a global system through the collaboration between people and government. The possible outcome is a model of a regulated and trusted cryptocurrency infrastructure that can be further tailored to different sectors with a different scheme.
The aim of the article. The purpose of the article is the theoretical substantiation of issues related to the system of strategic planning of economic development of industrial enterprises and marketing at the regional level in order to determine the interaction between them. The results of the analyses. The most characteristic features of modern strategic planning of the development of a production enterprise are considered: several strategic problems of the enterprise are solved; has a creative and iterative character; aimed at finding new business opportunities; It requires significant information, intellectual, as well as time costs; the basis of planning is the approach «from the future to the present»; differs stochastic approach and flexibility; strategic plans are conceptual and descriptive, which contain mainly qualitative and interval quantitative indicators; strategy development is based on the principle of alternatives; the system of strategic planning determines the potential of the company's success and creates the prerequisites for the effective operation of the enterprise; The subject of formation of the main strategic idea is the higher strategic level of enterprise management. Therefore, for business, the importance of the strategy is explained by the fact that clearly defined goals and guidelines for the development of the territory allow business entities to see the prospects of the economy, the prospects for development and state support of the industries, and, in accordance with new approaches and goals, declared by the local authorities in the planning documents, to build their own Plans for the future. In the conditions of objective incompleteness of information, the effect of external «deterrent factors» is multiplied, and therefore the mechanisms necessary to overcome them, which ensure the constructive nature of the processes of the flow of resources and capital in the economic space. One such mechanism is regional marketing. Some aspects of the interaction of the elements of the toolkit, which are fundamental in the formation of the system of strategic planning of the development of production enterprises and socio-economic development of the region, taking into account the marketing approach, are explored. Information interaction – the basis of the process of management of socio-economic development of the region, the mechanism for the development and implementation of both territorial strategies and strategies of production enterprises. Interaction through methods of managerial influence. Methods of economic interaction are a motivational component of the regional strategies of the region and the strategies of production enterprises. Methods of socio-psychological interaction. Interaction through project management and clustering. Interaction through the demand management system. Consequently, the main objective of marketing strategic planning is to build the activity of the territory and production enterprises in such a way that the organic and most efficient combination of production, satisfaction of the needs of consumers, profit and development of the region. The principles of marketing strategic planning are: coherence with overall strategic planning; based on the research of the marketing environment; cyclicity is a continuous process; flexibility – the ability to adapt the strategy to changes in the environment; multivariateness – taking into account possible changes of the environment at the stage of forming the plan. Conclusions and directions for further research. Thus, strategic planning of enterprise development in conditions of decentralization should be perceived as a powerful tool of state policy to ensure the balanced development of territorial communities. Consequently, three subjects of the national economy – government, business and the public, together, by consensus, create a joint strategy for the socio-economic development of the territory as a set of strategic goals, combined in the program of action based on the identified internal advantages and disadvantages of the socio-economic economic system, available resources, opportunities and threats to the environment. Keywords: strategic planning, economic development, manufacturing enterprises, regional marketing, methods of strategic planning. DOI: 10.15276/mdt.2.3.2018.7 Formuvannia obiednanykh terytorialnykh hromad: stan, problemni pytannia ta shliakhy yikh vyrishennia. Analitychna zapyska [Formation of united territorial communities: state, problem issues and ways of their solution. Analytical note]. www.niss.gov.ua Retrieved from http://www.niss. gov.ua/articles/2642/ [in Ukrainian]. Mischenko, A.P. (2007). Stratehichne upravlinnia [Strategic Management]. Dnipropetrovsk: DUEP [in Ukrainian]. Moskaluk V.E. (2005). Planuvannia diialnosti pidpryiemstva [Planning of enterprise activity]. K.: KNEU [in Ukrainian]. Ansoff, I. (1979). Strategicheskoe upravlenie [Strategic Management]. Moscow [in Russian]. Podolchak N.Y. (2012). Stratehichnyi menedzhment [Strategic Management]. Lviv: Lviv Polytechnic Publishing House [in Ukrainian]. Kotler, F., Asplund, K., & Rhine, I. (2005). Marketing mest: privlechenie investitsiy, predpriyatiy, zhiteley i turistov v goroda, kommunyi i stranyi: Stokgolmskaya shkola ekonomiki v Sankt-Peterburge. [Heider Marketing of places: attraction of investments, enterprises, residents and tourists to cities, communes and countries: Stockholm School of Economics in St. Petersburg]. St. Petersburg [in Russian]. Pankrukhin, A.P. (2006). Marketing territoriy [Territory Marketing]. St. Petersburg: Peter [in Russian]. Smentyna, N.V. (2015). Stratehichne planuvannia sotsialno-ekonomichnoho rozvytku na mezorivni: teoriia, metodolohiia, praktyka [Strategic planning of socio-economic development on mesorovnym: theory, methodology, practice]. Odessa: Atlanta [in Ukrainian]. Ruliev, V.A. (2011). Menedzhment [Management]. Kiev: Center for Educational Literature [in Ukrainian]. Mamonova, V, Baldic, N, & Grinchuk, N. (2013). Dzherela ta mekhanizmy finansuvannia mistsevoho ekonomichnoho rozvytku [Sources and mechanisms for financing local economic development]. Kiev [in Ukrainian]. Grinchuk, N. Formuvannia terytorialnykh marketynhovykh stratehii [Formation of territorial marketing strategies]. regionet.org.ua Retrieved from http://regionet.org.ua/files/08.Territorial_ Marketing_Grynchuk_Materials_UA.pdf [in Ukrainian]. Oklander, M. (2002). Problemy formuvannia marketynhovoi systemy krainy [Problems of forming of the marketing system of country]. Kiev [in Ukrainian]. Shchelkunov, V., Bondarenko, V., & Karakai, Y. (2005). Marketynh rehioniv: investytsiini aspekty [Marketing of the regions: investment aspects]. Kiev [in Ukrainian]. Kudenko, N.V. (2002). Marketynhovi stratehii firmy [Marketing strategies of the firm]. Kiev: KNEU [in Ukrainian]. Tiahunova, Z.O. (2011). Formuvannia mekhanizmu upravlinnya marketynhovym potentsialom pidpryiemstv systemy spozhyvchoy kooperatsii [Formation of the mechanism for managing the marketing potential of the enterprises of the system of consumer co-operation]. Naukovyy visnyk Chernivetskoho torhovelno-ekonomichnoho instytutu KNTEU [Scientific herald of the Chernivtsi Trade and Economic Institute KNTEU],3 (43), 320-323 [in Ukrainian]. Regional policy: legal regulation. World and Ukrainian experience. (2011). Tkachuk, A. (Ed). Kiev: Lesta [in Ukrainian]. On Approving the Model Provision on the Agency for Regional Development: Draft Resolution of the Cabinet of Ministers of Ukraine (2011, 20 June). old.csi.org.ua. Retrieved from http://old.csi.org.ua/?p=2395.
In this paper, we propose a new method to perform Sparse Kernel Principal Component Analysis (SKPCA) and also mathematically analyze the validity of SKPCA. We formulate SKPCA as a constrained optimization problem with elastic net regularization (Hastie et al.) in kernel feature space and solve it. We consider outlier detection (where KPCA is employed) as an application for SKPCA, using the RBF kernel. We test it on 5 real-world datasets and show that by using just 4% (or even less) of the principal components (PCs), where each PC has on average less than 12% non-zero elements in the worst case among all 5 datasets, we are able to nearly match and in 3 datasets even outperform KPCA. We also compare the performance of our method with a recently proposed method for SKPCA by Wang et al. and show that our method performs better in terms of both accuracy and sparsity. We also provide a novel probabilistic proof to justify the existence of sparse solutions for KPCA using the RBF kernel. To the best of our knowledge, this is the first attempt at theoretically analyzing the validity of SKPCA.
Reza M. Parizi, Ali Dehghantanha, Kim‐Kwang Raymond Choo, Amritraj Singh
The emerging blockchain technology supports decentralized computing paradigm shift and is a rapidly approaching phenomenon. While blockchain is thought primarily as the basis of Bitcoin, its application has grown far beyond cryptocurrencies due to the introduction of smart contracts. Smart contracts are self-enforcing pieces of software, which reside and run over a hosting blockchain. Using blockchain-based smart contracts for secure and transparent management to govern interactions (authentication, connection, and transaction) in Internet-enabled environments, mostly IoT, is a niche area of research and practice. However, writing trustworthy and safe smart contracts can be tremendously challenging because of the complicated semantics of underlying domain-specific languages and its testability. There have been high-profile incidents that indicate blockchain smart contracts could contain various code-security vulnerabilities, instigating financial harms. When it involves security of smart contracts, developers embracing the ability to write the contracts should be capable of testing their code, for diagnosing security vulnerabilities, before deploying them to the immutable environments on blockchains. However, there are only a handful of security testing tools for smart contracts. This implies that the existing research on automatic smart contracts security testing is not adequate and remains in a very stage of infancy. With a specific goal to more readily realize the application of blockchain smart contracts in security and privacy, we should first understand their vulnerabilities before widespread implementation. Accordingly, the goal of this paper is to carry out a far-reaching experimental assessment of current static smart contracts security testing tools, for the most widely used blockchain, the Ethereum and its domain-specific programming language, Solidity to provide the first...
Marko Hölbl, Marko Kompara, Aida Kamišalić, Lili Nemec Zlatolas
Blockchain technology enables a decentralized and distributed environment with no need for a central authority. Transactions are simultaneously secure and trustworthy due to the use of cryptographic principles. In recent years, blockchain technology has become very trendy and penetrated different domains, mostly due to the popularity of cryptocurrencies. One field where blockchain technology has tremendous potential is healthcare, due to the need for a more patient-centric approach to healthcare systems and to connect disparate systems and increase the accuracy of electronic healthcare records (EHRs). In this systematic review, an analysis of state-of-the-art blockchain research in the field of healthcare is conducted. The aim is to reveal the potential applications of the technology and to highlight the challenges and possible directions of blockchain research in healthcare. First, background information is discussed, followed by a description of the exact methodology used in this paper. Next, an analysis of the results is given, which includes a bibliometric overview, an analysis of gathered data and its properties, and the results of a literature quality assessment. Lastly, there is a discussion of the results from the analysis. The findings indicate that blockchain technology research in healthcare is increasing and it is mostly used for data sharing, managing health records and access control. Other scenarios are very rare. Most research is aimed at presenting novel structural designs in the form of frameworks, architectures or models. Findings also show that technical details about the used blockchain elements are not given in most of the analyzed publications and that most research does not present any prototype implementation or implementation details. Often even with a prototype implementation, no details about blockchain elements are given.
In-browser cryptojacking involves hijacking the CPU power of a website's visitor to perform CPU-intensive cryptocurrency mining, and has been on the rise, with 8500% growth during 2017. While some websites advocate cryptojacking as a replacement for online advertisement, web attackers exploit it to generate revenue by embedding malicious cryptojacking code in highly ranked websites. Motivated by the rise of cryptojacking and the lack of any prior systematic work, we set out to analyze malicious cryptojacking statically and dynamically, and examine the economical basis of cryptojacking as an alternative to advertisement. For our static analysis, we perform content-, currency-, and code-based analyses. Through the content-based analysis, we unveil that cryptojacking is a wide-spread threat targeting a variety of website types. Through a currency-based analysis we highlight affinities between mining platforms and currencies: the majority of cryptojacking websites use Coinhive to mine Monero. Through code-based analysis, we highlight unique code complexity features of cryptojacking scripts, and use them to detect cryptojacking code among benign and other malicious JavaScript code, with an accuracy of 96.4%. Through dynamic analysis, we highlight the impact of cryptojacking on system resources, such as CPU and battery consumption (in battery-powered devices); we use the latter to build an analytical model that examines the feasibility of cryptojacking as an alternative to online advertisement, and show a huge negative profit/loss gap, suggesting that the model is impractical. By surveying existing countermeasures and their limitations, we conclude with long-term countermeasures using insights from our analysis.
Block chain, or distributed ledger \n technology, has the potential to address many problems in \n emerging markets. In this note the authors consider whether \n block chain can be used to mitigate the problem of \n de-risking by financial institutions, which affects \n receivers of remittances, businesses that need correspondent \n banking relationships, and charities working in conflict \n countries. Block chain is an evolving technology, and \n understanding its scope and limitations will be critical to \n employing it to address these and related issues.
Permissionless blockchains reach decentralized consensus without requiring pre-established identities or trusted third parties, thus enabling applications such as cryptocurrencies and smart contracts. Consensus is agreed on data that is generated by the application and transmitted by the system's (peer-to-peer) network layer. While many attacks on the network layer were discussed so far, there is no systematic approach that brings together known attacks, the requirements, and the design space of the network layer. In this paper, we survey attacks on the network layer of permissionless blockchains, and derive five requirements: 1) performance; 2) low cost of participation; 3) anonymity; 4) DoS resistance; and 5) topology hiding. Furthermore, we survey the design space of the network layer and qualitatively show the effect of each design decisions on the fulfillment of the requirements. Finally, we pick two aspects of the design space, in-band peer discovery and relay delay, and demonstrate possible directions of future research by quantitatively analyzing and optimizing simplified scenarios. We show that while most design decisions imply certain tradeoffs, there is a lack of models that analyze and formalize these tradeoffs. Such models could aid the design of the network layer of permissionless blockchains. One reason for the lack of models is the deliberately limited observability of deployed blockchains. We emphasize that simulation based approaches cope with these limitations and are suited for the analysis of the network layer of permissionless blockchains.
Blockchain platforms such as Ethereum and several others execute complex transactions in blocks through user-defined scripts known as smart contracts. Normally, a block of the chain consists of multiple transactions of smart contracts which are added by a miner. To append a correct block into the blockchain, miners execute these transactions of smart contracts sequentially. Later the validators serially re-execute the smart contract transactions of the block. If the validators agree with the final state of the block as recorded by the miner, then the block is said to be validated. It is then added to the blockchain using a consensus protocol. In Ethereum and other blockchains that support cryptocurrencies, a miner gets an incentive every time such a valid block successfully added to the blockchain. In most of the current day blockchains the miners and validators execute the smart contract transactions serially. In the current era of multi-core processors, by employing the serial execution of the transactions, the miners and validators fail to utilize the cores properly and as a result, have poor throughput. By adding concurrency to smart contracts execution, we can achieve better efficiency and higher throughput. In this paper, we develop an efficient framework to execute the smart contract transactions concurrently using optimistic Software Transactional Memory systems (STMs). Miners execute smart contract transactions concurrently using multi-threading to generate the final state of blockchain. STM is used to take care of synchronization issues among the transactions and ensure atomicity. Now when the validators also execute the transactions (as a part of validation) concurrently using multi-threading, then the validators may get a different final state depending on the order of execution of conflicting transactions. To avoid this, the miners also generate a block graph of the transactions during the concurrent execution and store it in the block. This graph captures the conflict relations among the transactions and is generated concurrently as the transactions are executed by different threads. The miner proposes a block which consists of set of transactions, block graph, hash of the previous block, and final state of each shared data-objects. Later, the validators re-execute the same smart contract transactions concurrently and deterministically with the help of block graph given by the miner to verify the final state. If the validation is successful then proposed block appended into the blockchain and miner gets incentive otherwise discard the proposed block. We execute the smart contract transactions concurrently using Basic Time stamp Ordering (BTO) and Multi-Version Time stamp Ordering (MVTO) protocols as optimistic STMs. BTO and MVTO miner achieves 3.6x and 3.7x average speedups over serial miner respectively. Along with, BTO and MVTO validator outperform average 40.8x and 47.1x than serial validator respectively.
It is commonly believed that blockchain is a revolutionary technology for doing business on the Internet. Blockchain is a decentralized, distributed database or ledger of records. It ensures that the records are tamper-proof but publicly readable. Blockchain platforms such as Ethereum [3] and several others execute complex transactions in blocks through user-defined scripts known as smart contracts. Normally, a block of the chain consists of multiple transactions of smart contracts which are added by a miner. To append a correct block into the blockchain, miners execute these transactions of smart contracts sequentially. Later the validators serially re-execute the smart contract transactions of the block. If the validators agree with final state of the blocks as recorded by the miner, then the block is said to be valid and added to the blockchain using a consensus protocol.
Blockchain has received great attention in recent years and motivated innovations in different scenarios. However, many vital issues which affect its performance are still open. For example, it is widely convinced that high level of security and scalability and full decentralization are still impossible to achieve simultaneously. In this paper, we propose Bicomp, a bilayer scalable Nakamoto consensus protocol, which is an approach based on high security and pure decentralized Nakamoto consensus, and with a significant improvement on scalability. In Bicomp, two kinds of blocks are generated, i.e., microblocks for concurrent transaction packaging in network, and macroblocks for leadership competition and chain formation. A leader is elected at beginning of each round by using a macroblock header from proof-of-work. An elected leader then receives and packages multiple microblocks mined by different nodes into one macroblock during its tenure, which results in a bilayer block structure. Such design limits a leader's power and encourages as many nodes as possible to participate in the process of packaging transactions, which promotes the sharding nature of the system. Furthermore, several mechanisms are carefully designed to reduce transaction overlapping and further limit a leader's power, among which a novel transaction diversity based metric is proposed as the second level criteria besides the longest-chain-first principle on selecting a legitimate chain when fork happens. Security issues and potential attacks to Bicomp are extensively discussed and experiments for evaluation are performed. From the experimental results based on 50 nodes all over the world, Bicomp achieves significant improvement on scalability than that of Bitcoin and Ethereum, while the security and decentralization merits are still preserved.
Blockmania is a byzantine consensus protocol. Nodes emit blocks forming a directed acyclic graph (block DAG) that is subsequently interpreted by each node separately to ensure consensus with safety, liveness and finality. The resulting system has communication complexity $O(N^2)$ even in the worse case, and very low constant factors --- as compared to $O(N^4)$ for PBFT; it is leaderless; and network operations do not depend on the composition of the quorum or node stake. This makes Blockmania very efficient (leading to over 400K transactions per second on a wide area network), and ideal for dynamic membership and flexible and non-interrupted proof-of-stake protocols. A X-Blockmania variant, has $O(N)$ communication cost but also higher latency $O(\log N)$.