A fundamental open problem in the area of blockchain protocols is whether the Bitcoin protocol is the only solution for building a secure transaction ledger. A recently proposed and widely considered alternative is the \GHOST protocol which, notably, was proposed to be at the core of Ethereum as well as other recent proposals for improved Bitcoin-like systems. % The \GHOST variant is touted as offering superior performance compared to Bitcoin (potentially offering block production speed up by a factor of more than 40) without a security loss. Motivated by this, in this work, we study from a provable security point of view the \GHOST protocol.<br/><br/>We introduce a new formal framework for the analysis of blockchain protocols that relies on trees (rather than chains) and we showcase the power of the framework by providing a unified description of the \GHOST and Bitcoin protocols, the former of which we extract and formally describe. We then prove that \GHOST implements a ``robust transaction ledger'' (i.e., possesses liveness and persistence) and hence it is a provably secure alternative to Bitcoin; moreover, our bound for the liveness parameter is superior to that proven for the bitcoin backbone in line with the original expectation for \GHOST. Our proof follows a novel methodology for establishing that \GHOST is a robust transaction ledger compared to previous works, which may be of independent interest and can be applicable to other blockchain variants.
Thesis: S.M. in Real Estate Development, Massachusetts Institute of Technology, Program in Real Estate Development in conjunction with the Center for Real Estate, 2016.
Fiscal decentralization has been established in the People’s Republic of China (PRC), but crises emerge at the local government level due to remaining problems of the fiscal administration system of tax allocation and the impact of replacing the business tax with a value added tax. The PRC taxation system requires readjustment and local governments have begun to focus on innovative financing models. The main path to stable and sustainable government finances is to maintain the general public budget and the government fund budget. The present chapter shows that use of innovative fundraising and financing channels will lead to the upgrading of local government infrastructure and public services. Suggestions for enhancing local government fiscal stability and sustainability include: reducing the fiscal burden at the local level by standardizing and legalizing outlay establishing a modern taxation system; establishing a standardized and predictable transfer payment system by introducing block transfer payments and prioritized transfer payments as a basis for a stable growth mechanism for general transfer payments; promoting public–private partnership legislation to encourage participation of social capital and maximize the multiplier effect of public expenditure; and improving the mid-term budget and debt-annexed budget and establishing a government planning mechanism for investment and debt financing of major infrastructure construction projects.
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The current financial predicament of Local Government Councils and constant pressure for increase allocation has been in the front burner of Local Governments Administration in Nigeria. The focus of this paper therefore is an examination of Local Government Finance in Nigeria using Iwo Local Government as a Case Study. Data for the study were gathered from face-to-face interview, available records in Iwo Local Government, text books, lecture notes, journals, reports, seminar presentation and internet materials. The data collected were subjected to descriptive statistics (simple percentage) and content analysis. The study explored various sources of financing local governments in Nigeria. It also explained financial relationship of Nigerian local government vis-a-vis State and Federal Government using theory of decentralization. The study went further to explain financial management in Iwo L.G. Result obtained from the analysis shows that financial transfers from federal government (Statutory Federal Allocation) are the most viable and reliable source of local government revenue and that without Federal Allocation no capital project can be embarked on. Therefore, to arrest this financial situation that local government find itself, that is over dependence on federal allocation, this work submitted that local government should increase their revenue base by laying more emphasis on the internal revenue sources, especially those areas that are hitherto neglected or not been fully exploited. Keywords: Local Government, Administration, Finance, Decentralization, Nigeria, Iwo
The development of cryptocurrency technology has made it possible to transfer value securely and instantaneously without a third party intermediary such as a bank or financial institution. This is an exploratory analysis of where and why this technology has gained traction. In particular, I focus on the hypothesis that the relative popularity of cryptocurrency in Argentina can be explained by the presence of long-term capital controls. To test this hypothesis, I conducted expert interviews with market players. The main conclusion is that cryptocurrency can and has been used to evade capital controls. However, it is unlikely that substantial volumes have been moved via this mechanism. Cryptocurrency’s popularity in Argentina is attributable to more than the country’s history of capital controls or high rates of inflation. Other factors, including tax rate, levels of corruption, and history of multiple exchange rates have also contributed to adoption of this technology in Argentina. I propose further case study research on cryptocurrency in additional countries in order to develop these theories.
Tema ovog rada su kriptovalute. Budući da većina ljudi nije pravodobno upoznata s ovom temom, ovaj rad prikazuje i opisuje kriptovalute te način na koji se upotrjebljuju u svakodnevnom životu. Kriptovalute (eng. cryptocurrency) digitalne su valute dizajnirane kao sredstvo razmjene. Poznate su po tome što su državne agencije i banke isključene iz procesa razmjene. Kriptovalute omogućuju jednostavnu, jeftinu i brzu transakciju na području cijeloga svijeta. Trenutno najisplativije kriptovalute su Bitcoin i Ethereum, a u radu je opisana njihova korisnost, prednosti i mane. Budući da se Bitcoinu predviđa uspješna budućnost i sve je prisutniji i prihvatljiviji na tržištu, u radu su navedeni primjeri iz Hrvatske koji to potvrđuju. Sve veći broj poduzetnika odlučuje se za uvođenje kriptovaluta. U primjerima je obuhvaćen širok spektar djelatnosti, od frizerskih usluga, preko raznih tvrtki koji se bave prodajom računalne opreme, ugostiteljskih usluga preko mogućnosti brzog i lakog podizana gotovine na kripto bankomatima pa sve do plaćanja komunalnih usluga, pa čak i humanitarno djelovanje. Mnogi smatraju da su kriptovalute samo sinonim za prijevare i pranje novca, no programeri tvrde da su kriptovalute samo jedna vrsta tehnologije, alat koji sam po sebi ne može biti ni dobar ni loš, ovisno o tome za što se koristi. Autor ovoga rada proveo je istraživanje o tome kako se može besplatno započeti trgovanje kriptovalutama te je anketom ispitao stavove ispitanika o implementaciji kriptovaluta u društvu.
A technical article in 2008 and the follow-up open-source software in 2009 released by Satoshi Nakamoto have modified the concept of currency and seem to continue affecting our economic and financial thinking. In less than 8 years, bitcoin, a digital currency, is not only accepted as a mean of payment but also traded in numerous ?bitcoin exchanges?, which have accumulated a market capitalization of around 10.7 billion U.S. dollar. The phenomenon raised the interest of scholars across wide disciplines including finance, economics, law, and computer science. Research articles regarding bitcoin has gradually formed a growing body of literature, which reflects the state of the art of bitcoin research. However, there is no systematic survey of this literature up to now. The purpose of this study is to fill the gap by systematically surveying the bitcoin literature in the hope to uncover the main discussion topics and made suggestions for future research. We collect a total of 253 articles directly related to bitcoin from the Scopus database. In addition to providing basic descriptive statistics of this dataset, we apply co-word analysis to separate the literature into groups. This is done by establishing a network in which articles are nodes and co-usage of the key terms links these articles. The network is then separated into groups based on nodes? similarity in their connectivity. The result is a division of the articles into three groups each contain distinct discussion topics. The first group is a pool of technological articles which elaborates on improving various aspects of bitcoin technology. The second group focuses on bitcoin?s impacts to existing financial system and real economy. The discussions in the third group call for a legal framework to regulate bitcoin and other digital currency. In the end, we model the bitcoin research in a PEST (political, economic, social, and technological) analysis structure and suggest that the influence of bitcoin and the associated technology on society as a whole is a big gap waiting to be filled in future research.
Modern ocean exploration and sensing approaches have been mainly based on Autonomous Underwater Vehicles (AUVs), Remotely Operated Vehicles (ROVs), and/or static Underwater Acoustic Sensor Networks (UASNs) deployments. Individual AUVs and ROVs represent a single point of failure in addition to being bulky and expensive as vehicles are usually full-featured and sophisticated. UASNs have traditionally been statically deployed. This limits their use to original deployment locations and renders them unsuitable for search tasks. Swarm Robotics (SR) are a natural, better alternative. Swarms possess superior features over a sophisticated AUV; they are smaller, cheaper, robust, reliable, and scalable by design and definition. They also have the sensing capabilities of UASNs and built-in active mobility.\nDesigning successful swarm missions in harsh aquatic environments is an involved task. We address this by analyzing the indispensable stages of a typical mission and carefully designing decentralized algorithms to achieve the desired per-stage goals. Important system and environmental parameters are taken into consideration to achieve the end goal: completing mission requirements while respecting time constraint, with best possible performance and minimum loss of agents. Special attention is given to target search, task identification and allocation, and mission-stage integration due to their importance. Identifying target location in an unbounded environment is challenging. Bandwidth limited and intermittent communication complicates the process further. Therefore, we develop global search algorithms that use minimal communication and utilize flocking to maintain cohesion. These algorithms have multiple advantages over traditional ones in terms of convergence time, omni-directionality, consideration of physical constraints, and being self-bounding. At the target, tasks are autonomously identified and allocated in a completely decentralized manner. Validation of the developed techniques is done through realistic simulations and analytical comparisons.\nOur main contributions are: 1) a general framework for underwater mission planning, 2) three novel global search algorithms for unbounded underwater environment, 3) an algorithm for initial self-organization, 4) an optimized same-position reorientation algorithm for use in certain mission stages, 5) three autonomous task allocation algorithms, 6) three local target search algorithms, 7) a measure of mission utility, and 8) the design of a human brain-inspired model to support learning and complete autonomy.
Abstract Group encryption ( GE ) is the natural encryption analogue of group signatures in that it allows verifiably encrypting messages for some anonymous member of a group while providing evidence that the receiver is a properly certified group member. Should the need arise, an opening authority is capable of identifying the receiver of any ciphertext. As introduced by Kiayias, Tsiounis and Yung (Asiacrypt'07), GE is motivated by applications in the context of oblivious retriever storage systems, anonymous third parties and hierarchical group signatures. This paper provides the first realization of group encryption under lattice assumptions. Our construction is proved secure in the standard model (assuming interaction in the proving phase) under the Learning-With-Errors ( LWE ) and Short-Integer-Solution ( SIS ) assumptions. As a crucial component of our system, we describe a new zero-knowledge argument system allowing to demonstrate that a given ciphertext is a valid encryption under some hidden but certified public key, which incurs to prove quadratic statements about LWE relations. Specifically, our protocol allows arguing knowledge of witnesses consisting of X ∈ Z q m × n , s ∈ Z q n and a small-norm e ∈ Z m which underlie a public vector b = X ⋅ s + e ∈ Z q m while simultaneously proving that the matrix X ∈ Z q m × n has been correctly certified. We believe our proof system to be useful in other applications involving zero-knowledge proofs in the lattice setting.
Bitcoin has long been touted as a currency and a payment system that relies on cryptography and mathematics rather than trust. But is Bitcoin really trustless? And if so, would that be a good thing? This article undertakes a critical deconstruction of Bitcoin and the blockchain, their themes of democracy and transparency, and the idea that they are trustless. The article then proposes a new conceptualization of the role of trust in business and contracting: the bridging model, which allows for a more nuanced understanding of the interplay between enforcement and trust in contract formation. The bridging model is first applied to traditional banking, to illustrate and analyze the enforcement mechanisms underpinning the U.S. dollar as currency and the banking system as a whole, and to demonstrate that the enforcement mechanisms (government backing and regulation) are not as robust as generally believed. The bridging model is later applied to Bitcoin, to show not only that the system requires more trust than is generally understood, but also that both currency and payment systems benefit from the involvement of trusted intermediaries in response to problems and crises.
In this paper we describe ZKBoo <sup>1</sup>, a proposal for practically efficient zero-knowledge arguments especially tailored for Boolean circuits and report on a proof-of-concept implementation. As an highlight, we can generate (resp. verify) a non-interactive proof for the SHA-1 circuit in approximately 13ms (resp. 5ms), with a proof size of 444KB. Our techniques are based on the “MPC-in-the-head” approach to zero-knowledge of Ishai et al. (IKOS), which has been successfully used to achieve significant asymptotic improvements. Our contributions include: ◦ A thorough analysis of the different variants of IKOS, which highlights their pros and cons for practically relevant soundness parameters; ◦ A generalization and simplification of their approach, which leads to faster Σ-protocols (that can be made non-interactive using the Fiat-Shamir heuristic) for statements of the form “I know x such that y = φ(x)” (where φ is a circuit and y a public value); ◦ A case study, where we provide explicit protocols, implementations and benchmarking of zero-knowledge protocols for the SHA-1 and SHA-256 circuits.
Benoît Libert, San Ling, Khoa Nguyen, Huaxiong Wang
Abstract An accumulator is a function that hashes a set of inputs into a short, constant-size string while preserving the ability to efficiently prove the inclusion of a specific input element in the hashed set. It has proved useful in the design of numerous privacy-enhancing protocols, in order to handle revocation or simply prove set membership. In the lattice setting, currently known instantiations of the primitive are based on Merkle trees, which do not interact well with zero-knowledge proofs. In order to efficiently prove the membership of some element in a zero-knowledge manner, the prover has to demonstrate knowledge of a hash chain without revealing it, which is not known to be efficiently possible under well-studied hardness assumptions. In this paper, we provide an efficient method of proving such statements using involved extensions of Stern’s protocol. Under the Small Integer Solution assumption, we provide zero-knowledge arguments showing possession of a hash chain. As an application, we describe new lattice-based group and ring signatures in the random oracle model. In particular, we obtain: (i) the first lattice-based ring signatures with logarithmic size in the cardinality of the ring and (ii) the first lattice-based group signature that does not require any GPV trapdoor and thus allows for a much more efficient choice of parameters.
Bitcoin is a rising digital currency and exemplifies the grow- ing need for systematically gathering and analyzing pub- lic transaction data sets such as the blockchain. However, the blockchain in its raw form is just a large ledger listing transfers of currency units between alphanumeric character strings, without revealing contextually relevant real-world information. In this demo, we present GraphSense, which is a solution that applies a graph-centric perspective on digital currency transactions. It allows users to explore transactions and follow the money ow, facilitates analytics by semantically enriching the transaction graph, supports path and graph pattern search, and guides analysts to anomalous data points. To deal with the growing volume and velocity of transaction data, we implemented our solution on a horizontally scalable data processing and analytics infrastructure. Given the ongoing digital transformation in financial services and technologies, we believe that our approach contributes to development of analytics solutions for digital currency ecosystems, which is relevant in fields such as financial analytics, law enforcement, or scientific research