Bitcoin is one of the most prominent decentralized digital cryptocurrencies. Ability to understand which factors drive the fluctuations of the Bitcoin price and to what extent they are predictable is interesting both from the theoretical and practical perspective. In this paper, we study the problem of the Bitcoin short-term volatility forecasting based on volatility history and order book data. Order book, consisting of buy and sell orders over time, reflects the intention of the market and is closely related to the evolution of volatility. We propose temporal mixture models capable of adaptively exploiting both volatility history and order book features. By leveraging rolling and incremental learning and evaluation procedures, we demonstrate the prediction performance of our model as well as studying the robustness, in comparison to a variety of statistical and machine learning baselines. Meanwhile, our temporal mixture model enables to decipher the time-varying effect of order book features on volatility. It demonstrates the prospect of our temporal mixture model as an interpretable forecasting framework over heterogeneous Bitcoin data.
In this paper, we study the ability to make the short-term prediction of the exchange price fluctuations towards the United States dollar for the Bitcoin market. We use the data of realized volatility collected from one of the largest Bitcoin digital trading offices in 2016 and 2017 as well as order information. Experiments are performed to evaluate a variety of statistical and machine learning approaches.
The Internet pervades many aspects of modern life offering up seemingly boundless opportunities to connect, inform and be informed. As the range and number of sources for information online explode, how people go about selecting and interpreting information has become a pertinent area for study, not least in the recent light of the prevalence of fake-news—as people are well known to act upon information they believe to be trustworthy. Where the decision to act incurs risk, an inability to accurately select and assess the credibility of information presents a challenge. <br/><br/>This extended abstract summarizes findings from a study of 57 Bitcoin users. Our analysis shows that this self-identifying technical and expert community was not significantly influenced by confirmation bias (a facet of fake-news). However, the same users also failed to demonstrate a true reliance upon the facts contained in news articles, often deferring trust to the source of the news which could still render them susceptible to fake-news, and, in turn, place their speculation of the crypto-currency at risk.
This research work aims to study the intrinsic characteristics of the most \nrepresentative virtual currency among all the existing cryptocurrencies in the market, \nBitcoin, considering it under two points of view: as a means of payment in the \nexchange of goods and services and as a financial or investment asset for \nspeculative purposes in the short and medium term. \nLikewise, reference will be made to the different regulatory flows in terms of their \nlegal nature and, in particular, to the tax treatment in the European Union, the United \nStates and other selected jurisdictions. \nThe ultimate goal of this research is to analyze the current deficiencies of the global \nlegal status of Bitcoin in order to carry out the corresponding recommendations that \nallow an approximation to the global control of taxation and consumer protection.
Abstract This paper outlines how the digital currency and network technology of bitcoin functions and explores the context from which it emerged. Bitcoin was conceived in 2008 as an attempt to alleviate trust in government and banks which was at a low during this period of financial crisis. However, with bitcoin trust does not dissipate, rather it shifts. Trust moves from trust in banks or states to trust in algorithms and encryption software. There is a move from conventional trust in the gold standard—“In Gold We Trust”—to the trust announced on U.S. currency—“In God We Trust”—to trust in software and networks—“In Digital We Trust”. The hyperbole of bitcoin discourse is deemed to be an expression of the Californian Ideology, which itself often conceals a right-wing agenda. The paper analyses the hype behind the celebration of decentralised digital networks. It proposes that a form of network fetishism operates here. The failure of bitcoin as a currency (rather than as a hoarded commodity in an emergent bubble) and as an idea might be attributed to the failure to see how ultra-modern digital networks conceal very traditional consolidation of power and capital. The rise and fall of bitcoin, in terms of its original ambition, serves as a cautionary tale in the digital age—it reveals how ingenious innovations that might challenge power and the consolidation of capital become co-opted and colonised by capital. Finally, the paper offers a discussion of the possible progressive uses of the digital technology bitcoin has facilitated.
Tin Leelavimolsilp, Long Tran-Thanh, Sebastian Stein
Eyal and Sirer's selfish mining strategy has demonstrated that Bitcoin system is not secure even if 50% of total mining power is held by altruistic miners. Since then, researchers have been investigating either to improve the efficiency of selfish mining, or how to defend against it, typically in a single selfish miner setting. Yet there is no research on a selfish mining strategies concurrently used by multiple miners in the system. The effectiveness of such selfish mining strategies and their required mining power under such multiple selfish miners setting remains unknown. In this paper, a preliminary investigation and our findings of selfish mining strategy used by multiple miners are reported. In addition, the conventional model of Bitcoin system is slightly redesigned to tackle its shortcoming: namely, a concurrency of individual mining processes. Although a theoretical analysis of selfish mining strategy under this setting is yet to be established, the current findings based on simulations is promising and of great interest. In particular, our work shows that a lower bound of power threshold required for selfish mining strategy decreases in proportion to a number of selfish miners. Moreover, there exist Nash equilibria where all selfish miners in the system do not change to an honest mining strategy and simultaneously earn their unfair amount of mining reward given that they equally possess sufficiently large mining power. Lastly, our new model yields a power threshold for mounting selfish mining strategy slightly greater than one from the conventional model.
O objetivo do artigo consiste em responder ao seguinte problema de pesquisa: a falta de regulamentação específica para as criptomoedas possui relação com a expansão das modalidades criminosas? Para responder ao referido problema, é necessário abordar o conceito de criptomoedas, sua expansão, o papel das instituições de controle e os limites jurídicos que reconhecem a existência dessa nova modalidade de tecnologia. Partimos do suposto de que o advento das criptomoedas em si não consiste em uma atividade criminosa pela ausência de regulamentação pelo Banco Central, mas sim, pode vir a se encaixar em tipos penais pelo mau uso dos softwares. A abordagem é qualitativa, com suporte em revisão de literatura e análise descritiva dos fenômenos pesquisados, além da consulta sobre a legislação sobre o tema. A contribuição é relevante pelo ineditismo e pela importância do tema no contexto financeiro e jurídico das transações realizadas em modalidade virtual. Conclui-se que não é possível associar diretamente o uso de bitcoins com a expansão das modalidades criminosas, entretanto, resta evidente que há relação subjacente entre a falta de regulamentação e a especialização de práticas criminosas que usam o ciberespaço como ambiente.
Rodrigo Valente Giublin Teixeira, Felipe Rangel da Silva
Pelo presente se busca analisar o fenômeno da moeda eletrônica Bitcoin e o impacto jurídico por esta causado, especialmente no que cerne ao confronto aparente com a soberania estatal, uma vez que dada sua internacionalidade e a dificuldade ou impossibilidade de proibição do uso, poder-se-ia em um primeiro momento vislumbrar ofensa ao instituto jurídico, o que será desmistificado. Para tanto, utilizou-se de pesquisa bibliográfica, especialmente estrangeira, dado o ainda ineditismo do tema, com autores de áreas distintas da ciência jurídica, pois assim exigido para análise das questões técnicas de funcionamento da ferramenta e também para delimitação do impacto financeiro causado pela nova moeda, emprestando conceitos e institutos da ciência econômica para aplicação. Contudo, apesar de necessário, o aprofundamento interdisciplinar se restringe ao suficiente para possibilitar a análise jurídica, a qual se dá, por sua vez, em âmbito de Direito Público, não se tendo conhecimento de análise anterior realizada sob o mesmo prisma.
Jia Liu, Tibor Jager, Saqib A. Kakvi, Bogdan Warinschi
Time-lock encryption is a method to encrypt a message such that it can only be decrypted after a certain deadline has passed. We propose a novel time-lock encryption scheme, whose main advantage over prior constructions is that even receivers with relatively weak computational resources should immediately be able to decrypt after the deadline, without any interaction with the sender, other receivers, or a trusted third party. We build our time-lock encryption on top of the new concept of computational reference clocks and an extractable witness encryption scheme. We explain how to construct a computational reference clock based on Bitcoin. We show how to achieve constant level of multilinearity for witness encryption by using SNARKs. We propose a new construction of a witness encryption scheme which is of independent interest: our scheme, based on Subset-Sum , achieves extractable security without relying on obfuscation. The scheme employs multilinear maps of arbitrary order and is independent of the implementations of multilinear maps.
Artiklen betragter udviklingen i værdien af Bitcoin og stiller spørgsmålet, om der er en boble i Bitcoin - eller om prisudviklingen kan forklares ved nogle mere fundamentale karakteristika ved denne og andre kryptovalutaer eller måske af nogle teknoøkonomiske udviklingstendenser. Det er svært at komme med et entydigt svar på spørgsmålet, men ifølge artiklen er der flere forhold, der tyder på en boble.
Med introduktionen af et futures-marked er Bitcoin-eksponering blevet tilgængelig for en bredere gruppe af investorer, som hidtil ikke har kunnet eller villet tilgå det underliggende marked for Bitcoin. Artiklen finder, at kontrakterne umiddelbart favoriserer spekulanter på bekostning af hedgers og arbitragører, og analyserer, hvorledes futures-priserne kan indeholde væsentlig information om spekulaternes forventning til den fremtidige prisudvikling.
S. Nakamoto präsentierte 2008 eine Peer-to-Peer Version von elektronischem Geld: Bitcoin. Dieses System ermöglicht den direkten Zahlungsverkehr zwischen verschiedenen Personen und Organisationen, ohne Finanzdienstleister oder andere zu-vertrauende Dritte als Intermediäre einsetzen zu müssen. Im Zuge dessen entwickelte er die erste praktische Lösung für das Problem der Konsensfindung innerhalb eines dynamischen Netzwerks von potentiell anonymen Knoten, ohne die Notwendigkeit diese zuvor festzulegen. Dieses Ergebnis wird auf Basis des Konzepts von Proof-of-Work erzielt, das auf Grund der hohen Anforderungen für die benötigten Berechnungen zu einem enormen Energieverbrauch führt. Unter Verwendung des alternativen Prinzips von Proof-of-Stake versuchen neue Protokolle Nakamoto's Ansatz weiterzuentwickeln. Eine grundlegende Voraussetzung für die Sicherheit dieser Protokolle ist eine vertrauenswürdige (d. h. öffentlich-verifizierbare und manipulationssichere) Quelle von Zufallszahlen. Deren Erzeugung stellt ein komplexes Problem dar, da diese in einem dezentralen Netzwerk unter dem potentiellen Einfluss von Angreifern durchgeführt wird. Kürzlich veröffentlichte Forschungsergebnisse und Projekte aus der Wirtschaft beschäftigen sich mit diesem Problem und stellen sogenannte Random Beacon Protokolle vor, welche die erforderlichen Zufallszahlen in regelmäßigen Intervallen generieren. Diese Diplomarbeit beschäftigt sich intensiv mit den Herausforderungen der Entwicklung von Random Beacon Protokollen und liefert den ersten detaillierten Vergleich. Es wird gezeigt, dass Publicly-Verfiable Secret Sharing (PVSS) in vielen dieser Ansätze als gemeinsame Komponente dient. Weiters präsentiert diese Arbeit ein neu entwickeltes Protokoll, das ebenfalls PVSS verwendet und die Skalierbarkeit im Vergleich zu den bereits existierenden deutlich verbessert. Da dieser neue Ansatz nur eine PVSS-Instanz pro Runde benötigt, verringert sich der Kommunikationsaufwand von O(n³) auf O(n²). Diese Verbesserung wird erzielt, ohne auf wichtige Protokolleigenschaften, wie öffentliche Verifizierbarkeit, Manipulationssicherheit oder Nichtvorhersagbarkeit, verzichten zu müssen. Darüber hinaus erfolgt eine Optimierung der erarbeiteten Lösung durch die Entwicklung einer Protokollerweiterung, die die Interaktion zwischen den Knoten weiter reduziert und einen nahezu optimalen Kommunikationsaufwand von O(n c) erreicht. Dennoch stellt das erweiterte Protokoll mit sehr großer Wahrscheinlichkeit sicher, dass Zufallszahlen kontinuierlich erzeugt werden können und diese weder manipulierbar noch vorhersagbar sind.
Mikael Asplund, Jakob Lövhall, Simin Nadjm‐Tehrani
The possibility of in-store payments would further increase the potential usefulness of cryptocurrencies. However, this would require much faster transaction verification than current solutions provide (one hour for Bitcoin) since customers are likely not prepared to wait a very long time for their purchase to be accepted by a store. We propose a solution for enabling in-store payments with waiting times in the order of a few seconds, which is still compatible with the current Bitcoin protocol. The idea is based on a payment card in combination with a protocol for ensuring that losing a card does not mean losing the money on it. We analyse the required transaction verification delay and also the potentially added risks that the solution brings compared to current systems.
Open access
Blockchain Technology Applications and Security
IoT and Edge/Fog Computing
Advanced Steganography and Watermarking Techniques
In the Internet economy, with the help of cryptography, a branch of mathematics dealing with the security of information, as well as authentication and restriction of access to a computer system, a new digital coin as an alternative to national currencies appeared. In accomplishing this, using both mathematical methods (taking advantage of, for example, the difficulty of factorizing very large numbers), and quantum encryption methods. Throughout the world, information technology companies are focusing on information protection, inventing day-to-day methods with greater durability. In the horizon of Information Security, Quantum Cryptography has emerged, generating new possibilities in that field, hoping that data will be better protected and that the digital currency will resist over time and eventually evolve in the future, although Kurzweil, Bitcoin's pioneering technology is unlikely to be used in this respect. The idea of virtual alternatives to national currencies is not new, with advantages and disadvantages. The advantages of this coin are high payment freedom, transparency of information, high security, reduced risks for traders. Among the disadvantages we highlight the risk and volatility, the lack of notification and understanding, with incomplete functions, but which are developing, so Bitcoin is not perfect.
M Vaidehi, Alivia Pandit, Bhaskar Jindal, Minu Kumari · 5 authors
After the boom and bust in cryptocurrencies’ prices in recent years, Bitcoin has been totally regarded as an investment asset. As it is highly volatile in nature, there has been a need for good predictions for carrying base investment decisions. Although current study has used machine learning for more accurate Bitcoin price prediction, some of them did focused on the feasibility of applying different modeling techniques to the samples that has different data structures and dimension features. To predict Bitcoin price on different frequencies after using machine learning techniques, firstly we have to classify the Bitcoin price with daily price and high-frequency price. Here, we attempt to predict Bitcoin price as accurately as possible by taking into consideration various protocols that affect the Bitcoin value. Using the provided data we would predict the sign of daily price change with highest possible accuracy. We have used Random Forest Classifier and compared with benchmark results as daily price prediction, we achieve a better performance, with the highest accuracies of the statistical methods and machine learning algorithms of 99%. my investigation in Bitcoin price prediction can be considered as a pilot study for the importance of the sample dimension in the machine learning techniques. Keywords Bitcoin, Crypto Currency, Machine Learning, Blockchain, Long Short Term Memory(LSTM), Recurrent Neural Network(RNN), Prediction
We examine the significance of twenty-one potential drivers of bitcoin returns for the period 2010–2017 (2533 daily observations). Within a LASSO framework, we examine the effects of factors such as stock market returns, exchange rates, gold and oil returns, FED’s and ECB’s rates and internet trends on bitcoin returns for alternate time periods. Search intensity and gold returns emerge as the most important variables for bitcoin returns.
Elie Bouri, Mahamitra Das, Rangan Gupta, David Roubaud
This paper contributes to the embryonic literature on the relations between Bitcoin and conventional investments by studying return and volatility spillovers between this largest cryptocurrency and four asset classes (equities, stocks, commodities, currencies, and bonds) in bear and bull market conditions. We conducted empirical analyses based on a smooth transition VAR GARCH-in-mean model covering daily data from July 19, 2010 to October 31, 2017. We found significant evidence that Bitcoin returns are related quite closely to those of most of the other assets studies, particularly commodities, and therefore, the Bitcoin market is not isolated completely. The significance and sign of the spillovers exhibited some differences in the two market conditions and in the direction of the spillovers, with greater evidence that Bitcoin receives more volatility than it transmits. Our findings have implications for investors and fund managers who are considering Bitcoin as part of their investment strategies and for policymakers concerned about the vulnerability that Bitcoin represents to the stability of the global financial system.
The brave new world of blockchain potentially transforms the financial structures we have come to know and feel ambivalent about. What does a decentralized, secure system mean for our society?
Els conceptes de cadenes de blocs (blockchains) i contractes intel·ligents (smart contracts) ofereixen una alternativa sostenible en educació superior. Des d’aquest objectiu, es presenta una revisió d’ambdós conceptes i la seva relació amb els termes bitcoin, ledger, edublock i educoin. En un segon moment, s’atén a les xarxes en educació superior basades en tecnologia de cadenes de blocs, el seu vincle amb els contractes intel·ligents i les possibilitats a dia d’avui.
Elli Androulaki, Artem Barger, Vita Bortnikov, Christian Cachin · 21 authors
Fabric is a modular and extensible open-source system for deploying and operating permissioned blockchains and one of the Hyperledger projects hosted by the Linux Foundation (www.hyperledger.org). Fabric is the first truly extensible blockchain system for running distributed applications. It supports modular consensus protocols, which allows the system to be tailored to particular use cases and trust models. Fabric is also the first blockchain system that runs distributed applications written in standard, general-purpose programming languages, without systemic dependency on a native cryptocurrency. This stands in sharp contrast to existing blockchain platforms that require "smart-contracts" to be written in domain-specific languages or rely on a cryptocurrency. Fabric realizes the permissioned model using a portable notion of membership, which may be integrated with industry-standard identity management. To support such flexibility, Fabric introduces an entirely novel blockchain design and revamps the way blockchains cope with non-determinism, resource exhaustion, and performance attacks. This paper describes Fabric, its architecture, the rationale behind various design decisions, its most prominent implementation aspects, as well as its distributed application programming model. We further evaluate Fabric by implementing and benchmarking a Bitcoin-inspired digital currency. We show that Fabric achieves end-to-end throughput of more than 3500 transactions per second in certain popular deployment configurations, with sub-second latency, scaling well to over 100 peers.
An atomic cross-chain swap is a distributed coordination task where multiple parties exchange assets across multiple blockchains, for example, trading bitcoin for ether. An atomic swap protocol guarantees (1) if all parties conform to the protocol, then all swaps take place, (2) if some coalition deviates from the protocol, then no conforming party ends up worse off, and (3) no coalition has an incentive to deviate from the protocol. A cross-chain swap is modeled as a directed graph ${\cal D}$, whose vertexes are parties and whose arcs are proposed asset transfers. For any pair $({\cal D},L)$, where ${\cal D} = (V,A)$ is a strongly-connected directed graph and $L \subset V$ a feedback vertex set for ${\cal D}$, we give an atomic cross-chain swap protocol for ${\cal D}$, using a form of hashed timelock contracts, where the vertexes in $L$ generate the hashlocked secrets. We show that no such protocol is possible if ${\cal D}$ is not strongly connected, or if ${\cal D}$ is strongly connected but $L$ is not a feedback vertex set. The protocol has time complexity $O(diam({\cal D}))$ and space complexity (bits stored on all blockchains) $O(|A|^2)$.
Purpose The purpose of this paper is to examine the value-at-risk and related measures for the Bitcoin and to compare the findings with Standard and Poor’s SP500 Index, and the gold spot price time series. Design/methodology/approach A GJR-GARCH model has been implemented, in which the residuals follow the standardized Pearson type-IV distribution. A large variety of value-at-risk measures and backtesting criteria are implemented. Findings Bitcoin is a highly volatile currency violating the value-at-risk measures more than the other assets. With respect to the Basel Committee on Banking Supervision Accords, a Bitcoin investor is subjected to higher capital requirements and capital allocation ratio. Practical implications The risk of an investor holding Bitcoins is measured and quantified via the regulatory framework practices. Originality/value This paper is the first comprehensive approach to the risk properties of Bitcoin.
The emergence of a cryptocurrencies in the economic circulation is a challenge for legal systems. The response of a legal system depends on social, political and international determinants. The first attempts to understand cryptocurrencies usually concerns tax law, which, however, are related to the civilian understanding of the phenomenon. In the Polish legal system, we had a lack of regulation directly related to cryptocurrencies, which caused them to be strictly qualified as an instrument whose exchange for money was not exempt from VAT as Bitcoin was not classified as money. This situation has changed as a result of the case law of the Court of Justice of the European Union, which has recognized Bitcoin as an alternative means of payment. Recently, new statutory regulations have been introduced in non-European legal systems, i.e. in Japan and Arizona, which regulate cryptocurrencies in a wider way. This allows us to propose classification of legal systems based on the relationship they have towards cryptocurrencies.