Michał Polasik, Anna Piotrowska, Tomasz Piotr Wisniewski, Radosław Kotkowski · 5 authors
Over recent years, interest has been growing in Bitcoin, an innovation that has the potential to play an important role in e-commerce and beyond. The aim of our paper is to provide a comprehensive empirical study of the payment and investment features of Bitcoin, and their implications for the conduct of e-commerce. Since network externality theory suggests that the value of a network and its take-up are interlinked, we investigate both adoption and price formation. We discover that its returns are driven primarily by Bitcoin’s popularity, the sentiment expressed in newspaper reports on cryptocurrency, and total number of transactions. The paper also reports on the first global survey of merchants who have adopted this technology, and we model the share of sales paid for with this alternative currency, using both ordinary and Tobit regressions. Our analysis examines how country-, customer-, and company-specific characteristics interact with the proportion of sales attributed to Bitcoin. We find that company features, use of other payment methods, customers’ knowledge about Bitcoin, and the size of both the official and unofficial economy are significant determinants. The results will be of interest to traders who seek to understand factors driving prices and will help to inform vendors as to the most favorable circumstances for adopting the currency for online transactions.
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 users´ 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.
Joseph Bonneau, Arvind Narayanan, Andrew Miller, Jeremy Clark · 6 authors
Abstract. We propose Mixcoin, a protocol to facilitate anonymous payments in Bitcoin and similar cryptocurrencies. We build on the emergent phenomenon of currency mixes, adding an accountability mechanism to expose theft. We demonstrate that incentives of mixes and clients can be aligned to ensure that rational mixes will not steal. Our scheme is efficient and fully compatible with Bitcoin. Against a passive attacker, our scheme provides an anonymity set of all other users mixing coins contemporaneously. This is an interesting new property with no clear analog in better-studied communication mixes. Against active attackers our scheme offers similar anonymity to traditional communication mixes. 1
Bitcoin is a digital cryptocurrency that has generated considerable public interest, including both booms in value and busts of exchanges dealing in Bitcoins. One of the fundamental concepts of Bitcoin is that work, called mining, must be done in checking all monetary transactions, which in turn creates Bitcoins as a reward. In this paper we look at the energy consumption of Bitcoin mining. We consider if and when Bitcoin mining has been profitable compared to the energy cost of performing the mining, and conclude that specialist hardware is usually required to make Bitcoin mining profitable. We also show that the power currently used for Bitcoin mining is comparable to Ireland's electricity consumption.
Eli Ben‐Sasson, 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.
Adam Back, Matt Corallo, Luke Dashjr, Mark Friedenbach · 9 authors
Since the introduction of Bitcoin[Nak09] in 2009, and the multiple computer science and electronic cash innovations it brought, there has been great interest in the potential of decentralised cryptocurrencies. At the same time, implementation changes to the consensuscritical parts of Bitcoin must necessarily be handled very conservatively. As a result, Bitcoin has greater difficulty than other Internet protocols in adapting to new demands and accommodating new innovation. We propose a new technology, pegged sidechains, which enables bitcoins and other ledger assets to be transferred between multiple blockchains. This gives users access to new and innovative cryptocurrency systems using the assets they already own. By reusing Bitcoin’s currency, these systems can more easily interoperate with each other and with Bitcoin, avoiding the liquidity shortages and market fluctuations associated with new currencies. Since sidechains are separate systems, technical and economic innovation is not hindered. Despite bidirectional transferability between Bitcoin and pegged sidechains, they are isolated: in the case of a cryptographic break (or malicious design) in a sidechain, the damage is entirely confined to the sidechain itself. This paper lays out pegged sidechains, their implementation requirements, and the work needed to fully benefit from the future of interconnected blockchains.
Blockchain Technology Applications and Security
Cryptography and Data Security
Advanced Steganography and Watermarking Techniques
INTRODUCTION Since emerging from the Asian financial crisis of 1997–98, Indonesia has embarked on a period of steady economic expansion and growing prosperity. Even by East Asian standards its post-crisis growth has been rapid, and Indonesia joined the ranks of middle-income countries in 2011. The benefits of growth have been shared widely across the population and poverty has declined significantly. Economic growth coupled with prudent macroeconomic management has resulted in increasing revenues for the government, giving it the opportunity to invest more heavily in sectors vital to future development. Democratic decentralization began in parallel to multi-party elections at the national level in 1999. This has made locally elected governments responsible for providing basic public services to their electorates and shortened the lines of accountability between district populations and those responsible for local development. These trends have had far-reaching consequences for the education sector. Education has been a key beneficiary of increased government spending. In 2009, a constitutional obligation for government to commit a fifth of the total budget to education was first achieved, releasing an avalanche of new funding. Since 2001, decentralization of the education system has meant that local governments have played a more direct role in setting sectoral priorities and in managing and financing their education systems. The purpose of this chapter is to assess the impact that these changes, mainly the increased investment in education and the decentralization of management, have had on education sector performance. We will show that the recent increases in education spending by government and households alike have been associated with significant improvements in access to education, particularly among the poorest and most disadvantaged. Advancements in the quality of education, however, have been far harder to achieve. We argue that this disappointing result has been driven partly by unsuccessful but expensive policies aimed at improving teacher quality, but also by significant public spending inefficiencies at the district level associated with shortcomings in intergovernmental transfer mechanisms and weaknesses in local governance. Maintaining the impressive advances in the education sector will require improvements in the quality of spending. Improving governance of the education system will be crucial to these efforts.
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.
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.
Open access
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cs.CR
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Marcelo Arenas, Juan L. Reutter, Etienne Toussaint, Martín 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.
Groundwater tax is one type that is managed by the local tax . Tax groundwater previously managed by the provincial government then managed entirely by local governments as a form of decentralization . Implementation of tax policy at Tegal ground water is fully regulated in Regulation No. 2 of 2011 About Tax Groundwater . Authorized agency in terms of tax collection and management of ground water is Revenue Service, Management, Finance and Public Asset ( DPPKAD). Local regulations governing the issuance of tax policy groundwater is one of the efforts to preserve and control of groundwater use , so that it can be used on an ongoing basis and the tax function as a source of income to finance a useful area for regional development. This study aims to explain how tax policy implementation groundwater management in Tegal and identify aspects that support and hinder the implementation of tax policy groundwater managed by DPPKAD Tegal and is expected to become an input for implementing this policy. Supporting and inhibiting aspects identified aspects of the phenomenon of financial resources, economic conditions, social and political society, communication, and characteristics of the implementing agency. This is a descriptive qualitative study, using snowballing sampling technique. This study shows that the implementation of the groundwater tax already well proven with the successful achievement of the groundwater tax revenue , but there are some obstacles in its implementation. Many inhibiting factors that affect the implementation of groundwater tax collection, there are limited budget, yet comprehensive level of consciousness by taxpayer, and the lack of participation of the taxpayer and lack of socialization because DPPKAD has never held a formal socialization.
O. Rahamathunisa Begam, T. Manjula, T. Bharath Manohar, B. Susrutha
(Affiliated to JNTU Hyderabad)Hyderabad.Andhra Pradesh.India. ABSTRACT: Provable data possession (PDP) is a technique for ensuring the integrity of data in storage outsourcing. In this paper, we address the construction of an efficient PDP scheme for distributed cloud storage to support the scalability of service and data migration, in which we consider the existence of multiple cloud service providers to cooperatively store and maintain the clients ’ data. We present a cooperative PDP (CPDP) scheme based on homomorphic verifiable response and hash index hierarchy. We prove the security of our scheme based on multi-prover zero-knowledge proof system, which can satisfy completeness, knowledge soundness, and zero-knowledge properties. In addition, we articulate performance optimization mechanisms for our scheme, and in particular present an efficient method for selecting optimal parameter values to minimize the computation costs of clients and storage service providers. Our experiments show that our solution introduces lower computation and communication overheads in comparison with non-cooperative approaches.
RESUMO O presente artigo busca discorrer, ainda que brevemente, sobre um problema bastante discutido e controvertido, a admissibilidade das provas ilicitas no Direito de Familia, em que questoes de relevante interesse estao em jogo. Primeiramente, revela-se a garantia fundamental do direito a prova, decorrencia logica do direito constitucional de acao, inerente ao principio do devido processo legal e contraditorio. Em seguida, pretende-se analisar a prova ilicita no contexto das relacoes familiares. Palavras-chave: direito fundamental a prova. principios constitucionais. prova ilicita no Direito de Familia. RESUME: This Article seeks to discuss, albeit briefly, about an issue much debated and controversial, the admissibility of evidence illegal within Family Law, in which issues of relevant interest are at stake. First, it is a fundamental guarantee of the right to proof, logical consequence of the constitutional right of action, inherent to the principle of due legal process and contradictory. Then, seeks to analyze the evidence unlawful in the context of family relationships. Keywords: fundamental right to proof. constitutional principles. proof impermissible in family law.
One of important issues of information security in the interaction of users is the use of methods and tools, allowing one party to make sure of the authenticity of another party. The proof of knowledge protocols which have the additional property of zero-knowledge are applied to solve this problem. The protocols based on asymmetric encryption have received wide acceptance, such as the Fiat-Shamir, Schnorr, Okamoto, Guillou-Quisquater, Brickell-McCurley, Feige-Fiat-Shamir protocols. Cryptographic strength of these protocols is defined by discrete logarithms in a finite prime field, as well as an increase in the number of accreditation cycles. As a result of the development of methods and tools of cryptanalysis and rapid development of technologies and power of computing systems, there is a need to increase the sizes of system-wide parameters of the protocol, leading to increased resource intensity and performance complexity of basic operations in the fields.Cryptographic zero-knowledge protocols on elliptic curves are proposed in the paper. The strength of cryptosystems on elliptic curves is based on the difficulty of solving the discrete logarithm problem in the group of elliptic curve points, and is more difficult than the discrete logarithm problem in the finite field. The completeness and soundness of protocols were determined, computation examples were given. The tools of the Strength Protocol Animator package were applied to verify the protocols for resistance to enemy attacks. Consequently, the use of cryptographic protocols on elliptic curves will significantly reduce the sizes of protocol parameters and increase the cryptographic strength
Background: Accessibility to essential drugs is a public right, therefore it's the government responsibility to make them available.Previously before the era of regional autonomy, public drug management in all districts/cities was performed by the so-called District Pharmaceutical Warehouses (GFK).However, nowadays the situation has changed because of the difference in vision and perception of each regional government on the former warehouses.Some public drug management units in certain districts/cities are not functioning optimally.Inefficient drug procurement regarding the number and kind of drugs as well as timeliness results in gap between drug need and procurement.Furthermore, loosening in drug supply procedure makes essential drugs more unavailable to public.On the other hand, decentralization policy in drug management also undeniably brings advantages to the districts, for example capacity building in drug procurement, increasing capability in budget management and negotiation with district decision makers as well as enhancing regional economic activity.In revitalizing district pharmaceutical warehouses so as to attain minimal health care standards in districts/cities, baseline data in drug management and financing in several districts/cities should make a valuable contribution.Methods: A cross sectional descriptive study had been carried out during July-December 2006 in 26 districts/cities out of 11 provinces.Samples were 26 district health offices (Dinas Kesehatan Kabupaten/Kota) and 26 District Pharmaceutical Warehouses (GFK) where as respondents were head of drug section and head of warehousing respectively.Data were collected by means of structured questionnaires and in-depth interviews as well as the collection of secondary data of drug logistics.Qualitative and quantitative analysis was performed. Results:The study shows that: 1) although health budget in general had risen, the average percentage of drug budget allocation from 21 district health authorities was only 12.06%, reflecting the low drug priority in district health policy because drug expenditures may amount up to 40% of the total health budget.2) Public drug management was mostly performed by the so-called regional technical provider unit (UPTD) with some limitations concerning human resources and material in achieving an effective and efficient drug management, and 3) there was still lack of pharmacist assistants to manage drugs in primary health care (Puskesmas) up to 20% and even more piteously the lack of pharmacist in district drug management unit (GF/UPOP Kabupaten/Kota, 12,5%).Conclusions: Apart from the achievement of predetermined indicators stated in minimal health care standards in districts/ cities, especially regarding essential and generic drugs, drug management in general has been well performed concerning planning and drug availability.More support and commitment from the district government is a must considering that regional development can not be separated from the health development of the subject themselves.
Marcin Andrychowicz, Stefan Dziembowski, Daniel Malinowski, Łukasz 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.
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.