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9,726 results ¡ page 403 of 406
Tim Ruffing, Pedro Moreno-SĂĄnchez, Aniket Kate
No abstract is available for this record.
Florian Glaser, Kai Zimmermann, Martin Haferkorn, Moritz Weber ¡ 5 authors
Digital currencies are a globally spreading phenomenon that is frequntly and also prominently addressed by media, venture capitalists, financial and governmental institutions alike. As exchange prices for Bitcoin have reached multiple peaks within 2013, we pose a prevailing and yet academically unaddressed qustion: What are users' intentions when changing their domestic into a digital currency? In particular, this paper aims at giving empirical insights on whether usersĂ´ interest regarding digital currencies is driven by its appeal as an asset or as a currency. Based on our evaluation, we find strong indications that especially uninformed users approaching digital currencies are not primarily interested in an alternative transaction system but seek to participate in an alternative investment vehicle.
Eli BenâSasson, Alessandro Chiesa, Christina Garman, Matthew Green ¡ 7 authors
Bit coin is the first digital currency to see widespread adoption. While payments are conducted between pseudonyms, Bit coin cannot offer strong privacy guarantees: payment transactions are recorded in a public decentralized ledger, from which much information can be deduced. Zero coin (Miers et al., IEEE S&P 2013) tackles some of these privacy issues by unlinking transactions from the payment's origin. Yet, it still reveals payments' destinations and amounts, and is limited in functionality. In this paper, we construct a full-fledged ledger-based digital currency with strong privacy guarantees. Our results leverage recent advances in zero-knowledge Succinct Non-interactive Arguments of Knowledge (zk-SNARKs). First, we formulate and construct decentralized anonymous payment schemes (DAP schemes). A DAP scheme enables users to directly pay each other privately: the corresponding transaction hides the payment's origin, destination, and transferred amount. We provide formal definitions and proofs of the construction's security. Second, we build Zero cash, a practical instantiation of our DAP scheme construction. In Zero cash, transactions are less than 1 kB and take under 6 ms to verify - orders of magnitude more efficient than the less-anonymous Zero coin and competitive with plain Bit coin.
Miguel Freitas
This paper proposes a new microblogging architecture based on peer-to-peer networks overlays. The proposed platform is comprised of three mostly independent overlay networks. The first provides distributed user registration and authentication and is based on the Bitcoin protocol. The second one is a Distributed Hash Table (DHT) overlay network providing key/value storage for user resources and tracker location for the third network. The last network is a collection of possibly disjoint "swarms" of followers, based on the Bittorrent protocol, which can be used for efficient near-instant notification delivery to many users. By leveraging from existing and proven technologies, twister provides a new microblogging platform offering security, scalability and privacy features. A mechanism provides incentive for entities that contribute processing time to run the user registration network, rewarding such entities with the privilege of sending a single unsolicited ("promoted") message to the entire network. The number of unsolicited messages per day is defined in order to not upset users.
Lear Bahack
A widespread security claim of the Bitcoin system, presented in the original Bitcoin white-paper, states that the security of the system is guaranteed as long as there is no attacker in possession of half or more of the total computational power used to maintain the system. This claim, however, is proved based on theoretically flawed assumptions. In the paper we analyze two kinds of attacks based on two theoretical flaws: the Block Discarding Attack and the Difficulty Raising Attack. We argue that the current theoretical limit of attacker's fraction of total computational power essential for the security of the system is in a sense not $\frac{1}{2}$ but a bit less than $\frac{1}{4}$, and outline proposals for protocol change that can raise this limit to be as close to $\frac{1}{2}$ as we want. The basic idea of the Block Discarding Attack has been noted as early as 2010, and lately was independently though-of and analyzed by both author of this paper and authors of a most recently pre-print published paper. We thus focus on the major differences of our analysis, and try to explain the unfortunate surprising coincidence. To the best of our knowledge, the second attack is presented here for the first time.
Marcelo Arenas, Juan L. Reutter, Etienne Toussaint, MartĂn Ugarte ¡ 6 authors
In the consensus protocols used in most cryptocurrencies, participants called miners must find valid blocks of transactions and append them to a shared tree-like data structure. Ideally, the rules of the protocol should ensure that miners maximize their gains if they follow a default strategy, which consists on appending blocks only to the longest branch of the tree, called the blockchain. Our goal is to understand under which circumstances are miners encouraged to follow the default strategy. Unfortunately, most of the existing models work with simplified payoff functions, without considering the possibility that rewards decrease over time because of the game rules (like in Bitcoin), nor integrating the fact that a miner naturally prefers to be paid earlier than later (the economic concept of discount). In order to integrate these factors, we consider a more general model where issues such as economic discount and decreasing rewards can be set as parameters of an infinite stochastic game. In this model, we study the limit situation in which a miner does not receive a full reward for a block if it stops being in the blockchain. We show that if rewards are not decreasing, then miners do not have incentives to create new branches, no matter how high their computational power is. On the other hand, when working with decreasing rewards similar to those in Bitcoin, we show that miners have an incentive to create such branches. Nevertheless, this incentive only occurs when a miner controls a proportion of the computational power which is close to half of the computational power of the entire network.
Marcin Andrychowicz, Stefan Dziembowski, Daniel Malinowski, Ĺukasz Mazurek
BitCoin transactions are malleable in a sense that given a transaction an adversary can easily construct an equivalent transaction which has a different hash. This can pose a serious problem in some BitCoin distributed contracts in which changing a transaction's hash may result in the protocol disruption and a financial loss. The problem mostly concerns protocols, which use a "refund" transaction to withdraw a deposit in a case of the protocol interruption. In this short note, we show a general technique for creating malleability-resilient "refund" transactions, which does not require any modification of the BitCoin protocol. Applying our technique to our previous paper "Fair Two-Party Computations via the BitCoin Deposits" (Cryptology ePrint Archive, 2013) allows to achieve fairness in any Two-Party Computation using the BitCoin protocol in its current version.
Brian P. Hanley
Designed to compete with fiat currencies, bitcoin proposes it is a crypto-currency alternative. Bitcoin makes a number of false claims, including: solving the double-spending problem is a good thing; bitcoin can be a reserve currency for banking; hoarding equals saving, and that we should believe bitcoin can expand by deflation to become a global transactional currency supply. Bitcoin's developers combine technical implementation proficiency with ignorance of currency and banking fundamentals. This has resulted in a failed attempt to change finance. A set of recommendations to change finance are provided in the Afterword: Investment/venture banking for the masses; Venture banking to bring back what investment banks once were; Open-outcry exchange for all CDS contracts; Attempting to develop CDS type contracts on investments in startup and existing enterprises; and Improving the connection between startup tech/ideas, business organization and investment.
Richard Maxwell, Toby Miller
Bitcoin is the latest fantasy object of utopian thinkers far and wide. Angry with the banks? It sidesteps them. Fed up with governments? They canât regulate it. Annoyed by corporations? Bitcoin transcends them. Worried about fraud? Bitcoin uses the latest cryptography. Keen to make a buck (so to speak) by participating in a boom? Come on down and plug in.
Ladislav KriĹĄtoufek
Digital currencies have emerged as a new fascinating phenomenon in the financial markets. Recent events on the most popular of the digital currencies--BitCoin--have risen crucial questions about behavior of its exchange rates and they offer a field to study dynamics of the market which consists practically only of speculative traders with no fundamentalists as there is no fundamental value to the currency. In the paper, we connect two phenomena of the latest years--digital currencies, namely BitCoin, and search queries on Google Trends and Wikipedia--and study their relationship. We show that not only are the search queries and the prices connected but there also exists a pronounced asymmetry between the effect of an increased interest in the currency while being above or below its trend value.
Hitesh Dharmdasani
Nearly every aspect of a hacked computer and a users online life can be and has been commoditized. Recent trends into crypto currencies have made the former even more true as cyber criminals are now committing crime for monetary benefit and not just to out smart each other. In this study, I look more closely at Bitcoin, a de-centralized crypto currency which has become increasingly popular in the last six months. This study focuses on the analysis of the bitcoin economy, the involvement of malware and botnets and its effect to the currency.
Sarah Michelle Gruber
This Note discusses the relationship of Bitcoins, a cyber-currency, to the Bank Secrecy Act and discusses money laundering and tax evasion. This Note highlights the use and potentially problematic implications of Bitcoins in commerce and discusses their current regulation by the government, both within the United States and internationally, to guard against these threats. This Note addresses the regulation of Bitcoin exchanges, the exchanges' vulnerability to cyber-attacks, and the value of trust to the users of Bitcoin exchanges. This Note concludes that well known exchanges that operate both within and outside the United States generally self-regulate in order to gain the trust of their users despite the cyber-attacks on exchanges in the past. This Note also addresses the tax-reporting implications of foreign Bitcoin exchanges, looking by analogy at attempts to gain information from known tax havens.This Note argues that, given the applicability of the BSA to Bitcoin exchanges, the Bitcoin system poses serious questions relating to money laundering and tax reporting, mostly with regard to the less trustworthy exchanges known for their illegal activity. Some Bitcoin exchanges and e-wallets may also have the potential to become the next tax havens. Many exchanges voluntarily implement measures amounting to self-regulation in attempts to appear more trustworthy to wary consumers or in attempts to avoid criminal or civil sanctions. Whether this self-regulation is sufficient to achieve the goals of preventing money laundering and other criminal activity is debatable. Exchanges that have no need to appear trustworthy, however, still pose the same risks of money laundering and other illegal activity contemplated by the FBI. Moreover, ways exist in which criminals can work around the current regulatory scheme to achieve criminal goals; in that respect, the current regulatory scheme is ineffective to prevent the targeted criminal activity. This Note recommends a supplemental regulatory scheme that would target the areas that current regulation fails to address in combating money laundering, tax evasion, and other criminal activity.
Ittay Eyal, Emin GĂźn Sirer
The Bitcoin cryptocurrency records its transactions in a public log called the blockchain. Its security rests critically on the distributed protocol that maintains the blockchain, run by participants called miners. Conventional wisdom asserts that the protocol is incentive-compatible and secure against colluding minority groups, i.e., it incentivizes miners to follow the protocol as prescribed. We show that the Bitcoin protocol is not incentive-compatible. We present an attack with which colluding miners obtain a revenue larger than their fair share. This attack can have significant consequences for Bitcoin: Rational miners will prefer to join the selfish miners, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency. Selfish mining is feasible for any group size of colluding miners. We propose a practical modification to the Bitcoin protocol that protects against selfish mining pools that command less than 1/4 of the resources. This threshold is lower than the wrongly assumed 1/2 bound, but better than the current reality where a group of any size can compromise the system.
Nicolas T. Courtois, Marek Grajek, Rahul Naik
Bitcoin is a "crypto currency", a decentralized electronic payment scheme based on cryptography which has recently gained excessive popularity. Scientific research on bitcoin is less abundant. A paper at Financial Cryptography 2012 conference explains that it is a system which "uses no fancy cryptography", and is "by no means perfect". It depends on a well-known cryptographic standard SHA-256. In this paper we revisit the cryptographic process which allows one to make money by producing bitcoins. We reformulate this problem as a Constrained Input Small Output (CISO) hashing problem and reduce the problem to a pure block cipher problem. We estimate the speed of this process and we show that the cost of this process is less than it seems and it depends on a certain cryptographic constant which we estimated to be at most 1.86. These optimizations enable bitcoin miners to save tens of millions of dollars per year in electricity bills. Miners who set up mining operations face many economic incertitudes such as high volatility. In this paper we point out that there are fundamental incertitudes which depend very strongly on the bitcoin specification. The energy efficiency of bitcoin miners have already been improved by a factor of about 10,000, and we claim that further improvements are inevitable. Better technology is bound to be invented, would it be quantum miners. More importantly, the specification is likely to change. A major change have been proposed in May 2013 at Bitcoin conference in San Diego by Dan Kaminsky. However, any sort of change could be flatly rejected by the community which have heavily invested in mining with the current technology. Another question is the reward halving scheme in bitcoin. The current bitcoin specification mandates a strong 4-year cyclic property. We find this property totally unreasonable and harmful and explain why and how it needs to be changed.
Sarah Meiklejohn, Marjori Pomarole, Grant Jordan, Kirill Levchenko ¡ 7 authors
Bitcoin is a purely online virtual currency, unbacked by either physical commodities or sovereign obligation; instead, it relies on a combination of cryptographic protection and a peer-to-peer protocol for witnessing settlements. Consequently, Bitcoin has the unintuitive property that while the ownership of money is implicitly anonymous, its flow is globally visible. In this paper we explore this unique characteristic further, using heuristic clustering to group Bitcoin wallets based on evidence of shared authority, and then using re-identification attacks (i.e., empirical purchasing of goods and services) to classify the operators of those clusters. From this analysis, we characterize longitudinal changes in the Bitcoin market, the stresses these changes are placing on the system, and the challenges for those seeking to use Bitcoin for criminal or fraudulent purposes at scale.
Beat Weber
No abstract is available for this record.
Craig Warmke
Many want to know what bitcoin is and how it works. But bitcoin is as complex as it is controversial, and relatively few have the technical background to understand it. In this paper, I offer an accessible on-ramp for understanding bitcoin in the form of a model. My model reveals both what bitcoin is and how it works. More specifically, it reveals that bitcoin is a fictional substance in a massively coauthored story on a network that automates and distributes jobs normally entrusted to centralized publishing institutions. My model therefore falsifies a popular view according to which each bitcoin is a chunk of code.
Artus Krohn-Grimberghe, Christoph Sorge
Digital payment schemes show an ever increasing importance. Out of the countless different schemes available this article focuses on the popular Bitcoin system. The authors provide a description of Bitcoin's unique technological basis and its accompanying ecosystem of users, miners, trading platforms and vendors. Furthermore, this article discusses Bitcoin's currency-like features and the first regulatory actions take in the European Union and in the United States of America.
DĂĄniel Kondor, MĂĄrton PĂłsfai, IstvĂĄn Csabai, GĂĄbor Vattay
The possibility to analyze everyday monetary transactions is limited by the scarcity of available data, as this kind of information is usually considered highly sensitive. Present econophysics models are usually employed on presumed random networks of interacting agents, and only macroscopic properties (e.g. the resulting wealth distribution) are compared to real-world data. In this paper, we analyze BitCoin, which is a novel digital currency system, where the complete list of transactions is publicly available. Using this dataset, we reconstruct the network of transactions, and extract the time and amount of each payment. We analyze the structure of the transaction network by measuring network characteristics over time, such as the degree distribution, degree correlations and clustering. We find that linear preferential attachment drives the growth of the network. We also study the dynamics taking place on the transaction network, i.e. the flow of money. We measure temporal patterns and the wealth accumulation. Investigating the microscopic statistics of money movement, we find that sublinear preferential attachment governs the evolution of the wealth distribution. We report a scaling relation between the degree and wealth associated to individual nodes.
Beat Weber
The virtual currency and payment project Bitcoin intends to challenge the current monetary and payment system that finds itself in a legitimacy crisis in the aftermath of the financial market turmoil of 2008. In examining the governance of the Bitcoin system, I try to assess its potential to create input and output legitimacy as a payment system and as a monetary system in comparison with current practice.
Jansen, Mark A.
This paper concerns the open source software project Bitcoin, which is often described as virtual cash. The paper investigates what âvirtualâ signifies when applied to âcashâ and in turn what âvirtual cashâ says about Bitcoin. Bitcoin is the latest cryptographic effort to create digital cash-like tokens, where Bitcoinâs designer Nakamoto argues that users now no longer have to trust a third party, traditionally the bank. Paradoxically, for Bitcoin it is key that nodes in the network agree on the status of the shared block chain database. Trust remains to be established, albeit in a different manner. Power is not destroyed, but transferred from banks to Bitcoinâs protocol. The paper concludes that âvirtualâ refers to Bitcoinâs model of how cash appears to function in everyday exchange, allowing user privacy. Bitcoin does not model another aspect of cash, its function as a credential referring to debt. Bitcoin discontinues the concept of debt.
Amanda Talsma, Jan Sloots, Janneke van de Ouweland
Dit onderzoek is verricht voor het Lectoraat Duurzaam Financieel Management aan de Hanzehogeschool. Er wordt onderzocht welke gevolgen het gebruik van de Bitcoin heeft voor de maatschappij.
Morgen E. Peck
Bitcoin, the cryptocurrency powered by a decentralized peer-to-peer network of computers, has been hot this season. With the exchange rate bobbing around US $100, those involved in creating new bitcoins' and upholding the network that makes them valuable' have become locked in an arms race of sorts, seeking new, powerful machines that will enrich them but that could also destabilize the nascent virtual money.
J.A. Bergstra, Karl de Leeuw
A collection of questions about Bitcoin and its hypothetical relatives Bitguilder and Bitpenny is formulated. These questions concern technical issues about protocols, security issues, issues about the formalizations of informational monies in various contexts, and issues about forms of use and misuse. Some questions are formulated in the more general setting of informational monies and near-monies. We also formulate questions about legal, psychological, and ethical aspects of informational money. Finally we formulate a number of questions concerning the economical merits of and outlooks for Bitcoin.