To strengthen the anonymity of Bitcoin, several centralized coin-mixing providers (mixers) such as BitcoinFog.com, BitLaundry.com, and Blockchain.info assist users to mix Bitcoins through CoinJoin transactions with multiple inputs and multiple outputs to uncover the relationship between them. However, these mixers know the output address of each user, such that they cannot provide true anonymity. This paper proposes a centralized coin-mixing algorithm based on an elliptic curve blind signature scheme (denoted as Blind-Mixing) that obstructs mixers from linking an input address with an output address. Comparisons among three blind signature based algorithms, Blind-Mixing, BlindCoin, and RSA Coin-Mixing, are conducted. It is determined that BlindCoin may be deanonymized because of its use of a public log. In RSA Coin-Mixing, a user's Bitcoins may be falsely claimed by another. In addition, the blind signature scheme of Blind-Mixing executes 10.5 times faster than that of RSA Coin-Mixing.
The investments of Caixas and Institutos de Aposentadoria e Pensões (CAP and IAP) in homes of Natal, between the decades of 1930-60, helped to boost up the local real estate market in consolidation at the time. Inserted in the first national policy on social housing in the country, these operations have demanded the creation of a wide qualified organizational structure, which would be from the "Central Offices" of Rio de Janeiro to the decentralized units of the federal states. The professionals linked to the Local Agencies have developed, on this matter, from activities related to the design and construction of residential complexes, to the daily study of financing proposals in isolated units. As from these studies, the evaluation of shelters was essential to the effectiveness of the policy, resulting in the production of data on the market value of the properties by observing and issuing judgments upon the living quarters of different social groups. Given these considerations, the aim here is to contribute to the understanding on how to operate these real estate actions in the legitimization of boundaries about the urban space and dwellings available to workers in Natal. Therefore, the views of the city and constructions expressed by the evaluating engineers in their technical reports have been taken as the focus. Being the main primary sources of work, these reports are part of the edifices process of CAP/IAP regarding Natal, whose content is systematized in the database "Enterprises", the HCUrb Research Group. In addition, there were used local newspapers at the time and interviews with professionals as complementary sources. It was found that, in general, the evaluations have configured – in a more everyday dimension of bureaucratic routines - a vehicle, among others, circulating ideas about "home" within the social security institutions, being imbued with assumptions historically constructed about the "modern habitat". Filled in loco, the reports expose the clash between modernizing ideals in vogue and clear limitations in the city scenario at the time. Fragmented images of the town are given to read through the labels assigned to the evaluated sites – these being coated of certain "scientific" character - which both legitimated and contributed to the dynamics of appreciation/depreciation of the soil and to the socio-spatial differentiation. Contradictions were evident in the endorsement given by the technicians when financing of admittedly precarious homes for insured disadvantaged categories at the local level - such as industrial workers - while strict regulations were imposed to new construction, designed, above all, to better paid categories. By identifying raters engineers as urban agents, members of a technical-focused operating system for safety and efficiency in the real estate investments of those authorities corporatist, it is desired the usefulness of further studies on these characters, their training, professional activity and participation in the construction of discourses and practices of intervention about the city and its buildings, discussing individual and grouped interests that were left behind.
Abstract What does being money consist in? We argue that something is money if, and only if, it is typically acquired in order to realise the reduction in transaction costs that accrues in virtue of agents coordinating on acquiring the same thing when deciding what thing to acquire in order to exchange. What kinds of things can be money? We argue against the common view that a variety of things (notes, coins, gold, cigarettes, etc.) can be money. All monetary systems are best interpreted as implementing the same basic protocol. Money, i.e. the thing that we coordinate on acquiring in order to lower our transaction costs, is, in all cases, a set of positions on an abstract mathematical object, namely a relative ratio scale. The things that we ordinarily call ‘money’ are merely records of positions on such a scale.
More and more companies start offering digital payment systems. Smartphones evolve to a digital wallet such that it seems like we are about to enter the era of digital finance. In fact we are already inside an digital economy. The market of e-x (x = "finance", "money", "book", you name it . . . ) has not only picked up enormous momentum but has become standard for driving innovative activities of the global economy. A few clicks at y and payment at z brings our purchase to location w. Own currencies for the digital market were therefore just a matter of time. The idea of the Nobel Laureate Hayek, see [1], to let companies offer concurrent currencies seemed for a long time scarcely probabilistic, but the invention of the Blockchain made it possible to fill his vision with life. Cryptocurrencies (abbr. cryptos) came up and widened the angle towards this new level of economic interaction. Since bitcoins’ appearance a bunch of new cryptos spread the web and offered new ways of proliferation. The crypto market then fanned out and showed clear signs of acceptance and deep liquidity so that one has to look closer at the general moves and dynamics.
Craig K. Elwell, Margaret Murphy, Michael V. Seitzinger
This report has three major sections. The first section answers some basic questions about Bitcoin and the operation of the Bitcoin network and its interaction with the current dollar-based monetary system. The second section summarizes likely reasons for and against widespread Bitcoin adoption. The third section discusses legal and regulatory matters that have been raised by Bitcoin and other digital currencies.
Digital forensics must constantly adapt to new technological developments. The advent of Bitcoin is such a development. Bitcoin represents a new model for financial transactions. In many cash transactions between strangers, the underlying model is parties-unknown/transaction-unknown. There is no ledger record of the transaction. In contrast, PayPal illustrates the parties-known/transaction-known model. An intermediary will record both items of information. Bitcoin differs from both of these models; Bitcoin uses a parties-unknown/transaction-known model. The Bitcoin block chain records the transaction, but the user’s Bitcoin address is not expressly tied to an identity. Thus, Bitcoin users enjoy pseudo-anonymity.As the recent experience with Silk Road demonstrates, there is a downside to this pseudo-anonymity. Precisely because of that feature, Silk Road served a marketplace for vendors to sell illegal narcotics, forged identifications, and other illicit goods and services. Given that danger, law enforcement authorities have a felt need to develop techniques to penetrate the pseudo-anonymity. To do so, they have turned to digital forensics experts.This article evaluates two techniques that have been proposed for this purpose. The first is traffic analysis. This technique relies on the entry nodes that users employ to access the Internet. The second is transaction graph analysis. This technique clusters transactions to identify natural chokepoints in the Bitcoin economy, that is, service islands where, for example, the user might convert Bitcoins to fiat currency. The chokepoints becomes a target for a law enforcement subpoena to learn the user’s IP address. After describing each technique, the article assesses the research conducted to date. In particular, the article reviews Alex Biryukov’s research into traffic analysis and Sarak Meiklejohn’s work with transaction graph analysis. The article applies the standards announced in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) to determine whether, given the available data, expert testimony based on either technique would be admissible today. The article explains that it is doubtful whether testimony based on either technique would survive a Daubert admissibility challenge. The article concludes that further research is needed to enable law enforcement authorities to effectively penetrate the pseudo-anonymity of the new parties-unknown/transaction-known model.
Ittay Eyal, Adem Efe Gencer, Emin Gün Sirer, Robbert van Renesse
Cryptocurrencies, based on and led by Bitcoin, have shown promise as infrastructure for pseudonymous online payments, cheap remittance, trustless digital asset exchange, and smart contracts. However, Bitcoin-derived blockchain protocols have inherent scalability limits that trade-off between throughput and latency and withhold the realization of this potential. This paper presents Bitcoin-NG, a new blockchain protocol designed to scale. Based on Bitcoin's blockchain protocol, Bitcoin-NG is Byzantine fault tolerant, is robust to extreme churn, and shares the same trust model obviating qualitative changes to the ecosystem. In addition to Bitcoin-NG, we introduce several novel metrics of interest in quantifying the security and efficiency of Bitcoin-like blockchain protocols. We implement Bitcoin-NG and perform large-scale experiments at 15% the size of the operational Bitcoin system, using unchanged clients of both protocols. These experiments demonstrate that Bitcoin-NG scales optimally, with bandwidth limited only by the capacity of the individual nodes and latency limited only by the propagation time of the network.
Electronic financial transactions in the US, even those enabled by Bitcoin, have relatively high transaction costs. As a result, it becomes infeasible to make micropayments, i.e. payments that are pennies or fractions of a penny. In order to circumvent the cost of recording all transactions, Wheeler (1996) and Rivest (1997) suggested the notion of a probabilistic payment, that is, one implements payments that have expected value on the order of micro pennies by running an appropriately biased lottery for a larger payment. While there have been quite a few proposed solutions to such lottery-based micropayment schemes, all these solutions rely on a trusted third party to coordinate the transactions; furthermore, to implement these systems in today's economy would require a a global change to how either banks or electronic payment companies (e.g., Visa and Mastercard) handle transactions.
We show that equivocation, i.e., making conflicting statements to others in a distributed protocol, can be monetarily disincentivized by the use of crypto-currencies such as Bitcoin. To this end, we design completely decentralized non-equivocation contracts, which make it possible to penalize an equivocating party by the loss of its money. At the core of these contracts, there is a novel cryptographic primitive called accountable assertions, which reveals the party's Bitcoin credentials if it equivocates. Non-equivocation contracts are particularly useful for distributed systems that employ public append-only logs to protect data integrity, e.g., in cloud storage and social networks. Moreover, as double-spending in Bitcoin is a special case of equivocation, the contracts enable us to design a payment protocol that allows a payee to receive funds at several unsynchronized points of sale, while being able to penalize a double-spending payer after the fact.
Gaby G. Dagher, Benedikt Bünz, Joseph Bonneau, Jeremy Clark · 5 authors
Bitcoin exchanges function like banks, securely holding customers' bitcoins on their behalf. Several exchanges have suffered catastrophic losses with customers permanently losing their savings. A proof of solvency demonstrates cryptographically that the exchange controls sufficient reserves to settle each customer's account. We introduce Provisions, a privacy-preserving proof of solvency whereby an exchange does not have to disclose its Bitcoin addresses; total holdings or liabilities; or any information about its customers. We also propose an extension which prevents exchanges from colluding to cover for each other's losses. We have implemented Provisions and it offers practical computation times and proof sizes even for a large Bitcoin exchange with millions of customers.
Loi Luu, Jason Teutsch, Raghav Kulkarni, Prateek Saxena
Cryptocurrencies like Bitcoin and the more recent Ethereum system allow users to specify scripts in transactions and contracts to support applications beyond simple cash transactions. In this work, we analyze the extent to which these systems can enforce the correct semantics of scripts. We show that when a script execution requires nontrivial computation effort, practical attacks exist which either waste miners' computational resources or lead miners to accept incorrect script results. These attacks drive miners to an ill-fated choice, which we call the verifier's dilemma, whereby rational miners are well-incentivized to accept unvalidated blockchains. We call the framework of computation through a scriptable cryptocurrency a consensus computer and develop a model that captures incentives for verifying computation in it. We propose a resolution to the verifier's dilemma which incentivizes correct execution of certain applications, including outsourced computation, where scripts require minimal time to verify. Finally we discuss two distinct, practical implementations of our consensus computer in real cryptocurrency networks like Ethereum.
We provide a research-oriented introduction to the cryptographic currencies. We start with a description of Bitcoin and its main design principles. We then discuss some of its weaknesses, and show some ideas for dealing with them. We also talk about the mechanics of the mining pools and ideas for discouraging the mining pool creation. We provide an introduction to the smart contracts, and give some examples of them, including the multiparty lotteries.
2 source records
Blockchain Technology Applications and Security
Cryptography and Data Security
Advanced Steganography and Watermarking Techniques
Andrew Miller, Ahmed E. Kosba, Jonathan Katz, Elaine Shi
An implicit goal of Bitcoin's reward structure is to diffuse network influence over a diverse, decentralized population of individual participants. Indeed, Bitcoin's security claims rely on no single entity wielding a sufficiently large portion of the network's overall computational power. Unfortunately, rather than participating independently, most Bitcoin miners join coalitions called mining pools in which a central pool administrator largely directs the pool's activity, leading to a consolidation of power. Recently, the largest mining pool has accounted for more than half of network's total mining capacity. Relatedly, "hosted mining" service providers offer their clients the benefit of economies-of-scale, tempting them away from independent participation. We argue that the prevalence of mining coalitions is due to a limitation of the Bitcoin proof-of-work puzzle -- specifically, that it affords an effective mechanism for enforcing cooperation in a coalition. We present several definitions and constructions for "nonoutsourceable" puzzles that thwart such enforcement mechanisms, thereby deterring coalitions. We also provide an implementation and benchmark results for our schemes to show they are practical.
Back and Bentov (arXiv 2014) and Andrychowicz et al. (Security and Privacy 2014) introduced techniques to perform secure multiparty computations on Bitcoin. Among other things, these works constructed lottery protocols that ensure that any party that aborts after learning the outcome pays a monetary penalty to all other parties. Following this, Andrychowicz et al. (Bitcoin Workshop 2014) and concurrently Bentov and Kumaresan (Crypto 2014) extended the solution to arbitrary secure function evaluation while guaranteeing fairness in the following sense: any party that aborts after learning the output pays a monetary penalty to all parties that did not learn the output. Andrychowicz et al. (Bitcoin Workshop 2014) also suggested extending to scenarios where parties receive a payoff according to the output of a secure function evaluation, and outlined a 2-party protocol for the same that in addition satisfies the notion of fairness described above. In this work, we formalize, generalize, and construct multiparty protocols for the primitive suggested by Andrychowicz et al. We call this primitive secure cash distribution with penalties. Our formulation of secure cash distribution with penalties poses it as a multistage reactive functionality (i.e., more general than secure function evaluation) that provides a way to securely implement smart contracts in a decentralized setting, and consequently suffices to capture a wide variety of stateful computations involving data and/or money, such as decentralized auctions, market, and games such as poker, etc. Our protocol realizing secure cash distribution with penalties works in a hybrid model where parties have access to a claim-or-refund transaction functionality FCR}* which can be efficiently realized in (a variant of) Bitcoin, and is otherwise independent of the Bitcoin ecosystem. We emphasize that our protocol is dropout-tolerant in the sense that any party that drops out during the protocol is forced to pay a monetary penalty to all other parties. Our formalization and construction generalize both secure computation with penalties of Bentov and Kumaresan (Crypto 2014), and secure lottery with penalties of Andrychowicz et al. (Security and Privacy 2014).
<p>Bitcoin is a decentralized virtual crypto currency that has attracted attention from technologists, economists, consumers, regulators, black marketeers, venture capitalists and Wall Street commentators to name a few. While many debate issues such as whether or not bitcoin is money, how might it ultimately be regulated and whether or not it represents a truly disruptive innovation, this paper examines the current landscape of bitcoin and identifies some of the early adopters and significant events that have contributed to this unfolding phenomenon.</p>
This work reports on the experience arising from the master internship contract-based design tailored to safety issues for cyber-physical systems (CPS). The main educational goal is to confront the student with realistic mixed-critical smart CPS systems, using the railway domain and autonomous trains as a case study. The results show that, for this class of systems, education should transition from a 2D to a 3D modeling design space, which is much better suited to visualizing the evolution and the underlying properties of the system. We use contract-based design to properly deal with the integration and composition of heterogeneous components, where safety aspects require special attention. The main scientific and technical results concern the implementation of contract-based design in a 3D tool. Finally, we discuss the teaching methodology underlying the internship and the competences required to address the design of a (critical) CPS by the new generation of students.
ABSTRAKTujuan penelitian ini adalah untuk menguji pengaruh rasio keuangan (Rasio Derajat Desentralisasi, Rasio Ketergantungan Keuangan Daerah, Rasio Kemandirian Keuangan Daerah, Rasio Efekivitas Pendapatan Asli Daerah (PAD), Rasio Efisiensi Pendapatan Asli Daerah (PAD) dan Rasio Efektivitas Pajak Daerah) terhadap Indeks Pembangunan Manusia (IPM). IPM digunakan sebagai tolak ukur untuk menilai kinerja pemerintah daerah dalam hal penyediaan layanan publik. Populasi dalam penelitian ini adalah Pemerintah Provinsi di Indonesia. Data yang digunakan adalah Laporan Keuangan Pemerintah Daerah tahun 2010, 2011 dan 2012 untuk memprediksi IPM Provinsi tahun 2011, 2012 dan 2013. Data diperoleh dari website Badan Pemeriksa Keuangan dan dari website masing-masing pemerintah provinsi, kemudian dianalisis menggunakan regresi berganda.Hasil penelitian ini mengindikasikan bahwa Rasio Derajat Desentralisasi, Rasio Ketergantungan Keuangan Daerah dan Rasio Efektivitas Pajak Daerah berpengaruh terhadap Indeks Pembangunan Manusia (IPM). Sedangkan tiga viariabel independen yang lain tidak berpengaruh terhadap IPM. Penelitian ini memiliki keterbatasan, keterbatasan data tertentu sehingga populasi yang digunakan adalah pemerintah provinsi dan terbatas dalan waktu (tahun) yang digunakan dalam penelitian.Kata Kunci: Indeks Pembangunan Manusia (IPM), kinerja pemerintah provinsi, layanan publik, rasio keuangan.ABSTRACTThe purpose of this study was to examine the effect of financial ratios (Ratio Degree of Decentralization, Local Financial Dependency Ratio, Regional Financial Independence Ratio, Ratio Effectiveness of Locally Generated Revenue, Ratio Efficiency of Locally Generated Revenue and Ratio Effectiveness of Local Tax) to Human Development Index. Human Development Index is used as a benchmark to assess the performance of local governments in the provision of public services. The population in this study is the Provincial Government in Indonesia. The data used is the Local Government Finance Report in 2010, 2011 and 2012 to predict the Provincial Human Development Index in 2011, 2012 and 2013. Data were obtained from the website of the BPK RI and from the website of each provincial government, then analyzed using multiple regression.The results of this study indicate that the ratio of Degrees of Decentralization, Local Financial Dependency Ratio and Ratio Effectiveness of Local Tax effect on the Human Development Index (HDI). While the other three independent variable no effect on the HDI. This study has limitations, limitations specific data so that the population used is the provincial government and a limited role in time (years) used in the study.Keywords: Human Development Index (HDI), the performance of the provincial government, public services, financial ratios.
Fiscal system and organization of fiscal relations among different levels of public authorities are of great importance to the satisfaction of public needs at the state and local level as well as for the overall functioning of the socioeconomic system. The contemporary relations between the central and sub-central governments are strongly influenced by decentralization trends. At the same time, the processes of functional, fiscal and territorial decentralization are taking place in many states all over the world. Fiscal decentralization is necessary to achieve an appropriate distribution of public affairs (devolution of expenditure responsibilities) between the central and lower levels of government while ensuring sufficient public (fiscal) revenues to perform tasks in their area of responsibility. This transfer of responsibilities and functions to local and regional self-government should contribute to a more efficient system of public goods delivery that is in line with the expressed citizens’ preferences. The systems of local and regional self-government and models of financing of local and regional self-government are the key elements in achieving the fiscal decentralization goals. Therefore, in addition to
the review of theoretical insights into the fiscal system, fiscal decentralization and the system of regional and local self-governments, the subject of this paper is an analysis of the effects of fiscal decentralization on the model of financing of local and regional self-governments in the Republic of Croatia in the period from 2003 to 2013, as well as proposal of measures (guidelines) that would result with improvement of the existing model in the area of individual financing (budget) sources and uses of the EU funds. The expected scientific contribution of the paper is achieved by proving the research hypotheses and suggesting the improved model of financing of local and regional self-governments under the assumption of retaining the same expenditure responsibility division among different government levels and the same territorial organization. The structure of the paper is divided into seven chapters. After the introductory part, the basic theoretical knowledge and features of the fiscal system and fiscal decentralization are explained in the second chapter. Special attention is dedicated to the structure of fiscal system, the theoretical principles of fiscal federalism, the relations between decentralization and macroeconomic variables, the implementation of fiscal decentralization programs and the fiscal decentralization indicators. The third chapter gives an overview of the basic concepts related to local and regional self-government, and considers its role and importance in the system of the public governments. The research framework and the methodology of scientific research used in the paper are presented in the fourth chapter. The fifth chapter of the paper contains the research results of the system of local and regional self-government in the Republic of Croatia. The research covers the administrative and territorial structure of local and regional self-government, the model of financing of the local and regional selfgovernment, as well as the effects of fiscal decentralization on local and regional selfgovernment budgets in the period from 2003 to 2013. The research results and possible measures for improvement of the existing model of financing of the local and regional self-government according to the individual financing sources of budget revenues are discussed and presented in the sixth chapter. Additionally, possibilities and ways of using the available money from the EU structural funds to finance projects within the framework of financing model of the local and regional self-government are considered. The most important results of the scientific research on the functioning and financing of the local and regional self-government in the Republic of Croatia are systematically presented in the concluding chapter of the paper.