Alexandru Pîrjan, Dana-Mihaela Petroșanu, Mihnea Huth, Mihaela Negoiță
In this paper, we research and analyse the main characteristics, the evolution of the Bitcoin and of the Alternative Coins (Alt-Coins) digital currencies, their numerous applications and ramifications. We make an in depth analysis of the Bitcoin digital currency and of the most significant Alternative Coins, taking into account their technical characteristics, their main advantages and limitations. Just as it happened in the past decades with the personal computers and Internet, the impact of these digital currencies will gradually increase in the future, leading to major changes in our lifestyle, redefining our everyday life, economy and society.
In this concept paper, we report on ongoing work aimed at a novel approach to developing complex products. Based on an analysis of the requirements of product development in the automotive industry, the main problems we observe are limited transparency, patency, and reuse. These problems are even more pronounced - and more difficult to manage - in multi-brand product development settings, with spatially distributed and organizationally autonomous development partners. In order to decrease the amount of information each actor has to manage, we propose and illustrate the novel notion of virtual product model components (VPM-C) as an approach to address these challenges. We propose a conceptual architecture of virtual product models, which supports four concepts (views) as first-class citizens: parts, geometries, features, and processes. To handle the dependencies between elements of a VPM-C, we further suggest an agent-based approach, and outline a corresponding architectures and design alternatives. We illustrate these basic concepts by use case scenarios derived from an analysis of automotive product development practices.
Large computations, when amenable to distributed parallel execution, are often executed on computer clusters, for scalability and cost reasons. Such computations are used in many applications, including, to name but a few, machine learning, webgraph mining, and statistical machine translation. Oftentimes, though, the input data is private and only the result of the computation can be published. Zero-knowledge proofs would allow, in such settings, to verify correctness of the output without leaking (additional) information about the input.
Cinzia Di Novi, Massimiliano Piacenza, Silvana Robone, Gilberto Turati
This paper aims at investigating empirically the impact of fiscal decentralization reforms on inequality in well-being. In particular, we look at the effects on health inequalities following the assignment of larger tax power to the Italian Regions for financing their health expenditure, starting from the end of the Nineties. Exploiting large differences in the size of the tax base across Regions, we find that fiscal decentralization processes that attribute a greater tax power to lower government tiers, besides reducing inefficiencies of healthcare policies, seem to be effective in reducing also within-regional disparities in health outcomes. However, the degree of economic development � on which depends the actual fiscal autonomy from Central government � significantly affects the effectiveness of these reforms and highlights the importance to take properly into account the specific features of the context where the decentralization of power is implemented.
Bitcoin has become the de facto 'gold' standard among cryptocurrencies as it is the most widely accepted in commerce, has the largest mining network, and greatest volume of transactions. Because of this, miners of other SHA-256 cryptocurrencies will tend to convert those altcoins into bitcoin in order to transact in a meaningful way with the real economy. The result is that bitcoin mining regulates that of all other SHA-256 blockchains. Specifically, what matters is the expected number of bitcoins produced per day given a unit of hashing (mining) power, whatever the equivalence in the coin being mined. If mining for a different coin would yield a greater return in bitcoins at the margin (per day) for a miner, an apparent arbitrage opportunity will exist to direct mining effort at that cryptocurrency and subsequently exchange those for bitcoin. These opportunities, once taken, quickly eliminate the profitable arbitrage and appear to operate in a fairly efficient and predictable manner. A model is developed in this paper to formalize this process where cryptocurrency miners seeking to maximize production in terms of bitcoins earned in a day will exploit any such opportunities. If no such opportunities exist, they will simply revert to mining bitcoins directly. There are some important implications to this process, such as a tendency for cryptocurrencies to fall in price relative to bitcoin over time, and for changes in bitcoin mining difficulty to indirectly influence the market prices of altcoins. Finally, it seems that those undertaking this process of miners' arbitrage do so at the expense of speculators and noise traders who make decisions regarding buy and sell trades without the use of fundamental data. These participants generally have poor timing, follow trends, and over-react to good and bad news. Altcoins are produced by miners and subsequently offered for sale in the market in order to obtain bitcoins; meanwhile noise traders serve as the only bid-side to the market, on average.
Feng Mai, Qing Bai, Jay Shan, Xin Wang · 5 authors
As the world's first completely decentralized digital payment system, the emergence of Bitcoin represents a revolutionary phenomenon in financial markets. This study examines the dynamic relationships between social media and bitcoin performance. We consider the distinct effects of different social media platforms and different user groups subdivided by posting volume. The results suggest that more bullish forum posts have a positive effect on bitcoin returns, and the effect is stronger when we only include the posts by users who are less likely to contribute. In addition, messages on Internet forum have stronger impacts on future bitcoin market measures at a daily frequency, but microblogs’ effects are more significant at an hourly frequency.
This paper assesses costs and benefits of regulating Bitcoin. A review of the main justifications for regulating it shows that scope for efficient regulation is limited. Private governance structures and fee-based services have already begun addressing many of the known problems. Furthermore, since a regulation would discourage use, the costs—in terms of technological gains forgone—are potentially high. Nonetheless, there is scope for regulation, to ensure one has recourse in the event of theft, as long as the following are addressed: 1) provide a clear regulatory framework; 2) supervise transactions to dissuade crime, without compromising the medium; 3) regulate exchanges, rather than users; 4) encourage technological progress by committing to an environment of permissionless innovation.
Motivated by the goal of removing trusted setup assumptions from cryptography, we introduce the notion of witness signatures. This primitive allows any party with a valid witness to an NP statement to sign a message on behalf of that statement. We also require these signatures to be unforgeable: that is, producing a signature on a new message (even given several message, signature pairs) should be as hard as computing a witness to the NP statement itself. Witness signatures are closely related to previously well-studied notions such as non-malleable non-interactive zero knowledge arguments, and signatures of knowledge. In this work, we formalize this notion and show that most natural definitions are impossible in the plain model without any setup assumptions. While still wanting to avoid a central trusted setup, we turn to the tamper proof hardware token model of Katz (Eurocrypt 2007). Interestingly, we show witness signatures in the hardware token model are closely related to what we call non-malleable multi-prover zero-knowledge proofs in the plain model (i.e. without hardware tokens). We initiate the study of non-malleable multi-prover zero-knowledge proofs, and, provide an unconditional construction of single round non-malleable two-prover zero-knowledge proofs. We then use this primitive to obtain an unconditional
Les devises électroniques décentralisées, comme Bitcoin*, reposent sur un même principe : elles sont émises et gérées sans autorité centrale et ne dépendent d’aucun gouvernement, banque ou autre institution centralisée. Toutes les transactions sont régies par un protocole cryptographique open source et sont enregistrées sur un registre public (ou blockchain) maintenu par un réseau de pairs distribués dans le monde entier. Ce principe initial a été modifié pour de nouvelles applications afin d...
This paper aims to identify the likely determinants for cryptocurrency value formation, including for that of bitcoin. Due to Bitcoin’s growing popular appeal and merchant acceptance, it has become increasingly important to try to understand the factors that influence its value formation. Presently, the value of all Bitcoins in existence represent approximately $7 billion, and more than $60 million of notional value changes hands each day. Having grown rapidly over the past few years, there is now a developing but vibrant marketplace for bitcoin, and a recognition of digital currencies as an emerging asset class. Not only is there a listed and over-the-counter market for bitcoin and other digital currencies, but also an emergent derivatives market. As such, the ability to value bitcoin and related cryptocurrencies is becoming critical to its establishment as a legitimate financial asset.Using cross-sectional empirical data examining 66 of the most widely used cryptocurrencies, a regression model was estimated that points to three main drivers of cryptocurrency value: the level of competition in the network of producers, the rate of unit production, and the difficulty of algorithm used to “mine” for the cryptocurrency. These amount to relative differences in the cost of production of one digital currency over another at the margin, pointing to differences in relative cost of production – electricity goes in, cryptocurrency comes out. Using that as a starting point, a no-arbitrage situation is established for Bitcoin-like cryptocurrencies followed by the formalization of a cost of production model to determine the fair value of a bitcoin.
We describe a new methodology that enables the di-rect execution of multi-threaded applications inside of Shadow, an existing parallel discrete-event network sim-ulation framework. Our methodology utilizes function interposition and an application-layer thread library to emulate the ordinary thread interface to the application. Using this methodology, we implement a new Shadow plug-in that directly executes the Bitcoin reference client software. We describe optimizations that enable scalable execution of thousands of Bitcoin nodes on a single ma-chine, and discuss how to model the Bitcoin network for experimental purposes. Finally, we present novel denial-of-service attacks against the Bitcoin software, which exploit low-level implementation artifacts in the Bitcoin reference client. We demonstrate these attacks using our methodology, tools, and models. 1
Martina Matta, Maria Ilaria Lunesu, Michele Marchesi
In the last decade, Web 2.0 services such as blogs, tweets, forums, chats, email etc. have been widely used as communication media, with very good results. Sharing knowledge is an important part of learning and enhancing skills. Furthermore, emotions may affect decisionmaking and individual behavior. Bitcoin, a decentralized electronic currency system, represents a radical change in financial systems, attracting a large number of users and a lot of media attention. In this work, we investigated if the spread of the Bitcoin’s price is related to the volumes of tweets or Web Search media results. We compared trends of price with Google Trends data, volume of tweets and particularly with those that express a positive sentiment. We found significant cross correlation values, especially between Bitcoin price and Google Trends data, arguing our initial idea based on studies about trends in stock and goods market.
Patrick McCorry, Siamak F. Shahandashti, Dylan Clarke, Feng Hao
Abstract. Bitcoin is designed to protect user anonymity (or pseudonymity) in a financial transaction, and has been increasingly adopted by major e-commerce websites such as Dell, PayPal and Expedia. While the anonymity of Bitcoin transactions has been extensively studied, little attention has been paid to the security of post-transaction correspondence. In a commercial ap-plication, the merchant and the user often need to engage in follow-up corre-spondence after a Bitcoin transaction is completed, e.g., to acknowledge the receipt of payment, to confirm the billing address, to arrange the product de-livery, to discuss refund and so on. Currently, such follow-up correspondence is typically done in plaintext via email with no guarantee on confidentiality. Obviously, leakage of sensitive data from the correspondence (e.g., billing ad-dress) can trivially compromise the anonymity of Bitcoin users. In this paper, we initiate the first study on how to realise end-to-end secure communica-tion between Bitcoin users in a post-transaction scenario without requiring any trusted third party or additional authentication credentials. This is an important new area that has not been covered by any IEEE or ISO/IEC se-curity standard, as none of the existing PKI-based or password-based AKE schemes are suitable for the purpose. Instead, our idea is to leverage the Bit-coin’s append-only ledger as an additional layer of authentication between previously confirmed transactions. This naturally leads to a new category of AKE protocols that bootstrap trust entirely from the block chain. We call this new category “Bitcoin-based AKE ” and present two concrete protocols: one is non-interactive with no forward secrecy, while the other is interactive with additional guarantee of forward secrecy. Finally, we present proof-of-concept prototypes for both protocols with experimental results to demonstrate their practical feasibility.
Available online xxxx We explain stable growth performance in democracies by characterizing political systems in terms of the distribution of political power across groups, and show when the qualities of policy alternatives are uncertain, greater democracy (decentralization of authority) leads to more stable policy choices. We empirically test this mechanism by creating measures of the intertemporal variability in fiscal and trade policies. In an array of specifications (cross-sectional, panel with fixed-effects, matching models, instrumental variables, difference-in-difference), we show that policy choices are significantly more stable over time in democracies. This mechanism explains a large part of the negative link between democracy and output volatility.
In this paper, the fault detection and diagnosis problems are considered for a class of discrete nonlinear systems with decentralized event-triggered measurement transmissions. Each sensor determines, according to certain triggering rules, whether to transmit the present measurement to remote filters based on only locally available information. A set of filters is designed where each filter aims to jointly estimate the system states and a specific possible fault. Upper bounds of the estimation error covariances are obtained in the simultaneous presence of the linearization errors and decentralized event-triggered transmissions, and then the filter gains are calculated to minimize such bounds. The filters are designed in a recursive way and thus the algorithm is applicable for online implementation. When a fault is detected, the filter with the least residual is regarded as the one corresponding to the actual fault and its output can be seen as the states and fault estimation. The effectiveness of the proposed method is illustrated by a simulation example.