As the most successful cryptocurrency to date, Bitcoin constitutes a target of choice for attackers. While many attack vectors have already been uncovered, one important vector has been left out though: attacking the currency via the Internet routing infrastructure itself. Indeed, by manipulating routing advertisements (BGP hijacks) or by naturally intercepting traffic, Autonomous Systems (ASes) can intercept and manipulate a large fraction of Bitcoin traffic. This paper presents the first taxonomy of routing attacks and their impact on Bitcoin, considering both small-scale attacks, targeting individual nodes, and large-scale attacks, targeting the network as a whole. While challenging, we show that two key properties make routing attacks practical: (i) the efficiency of routing manipulation; and (ii) the significant centralization of Bitcoin in terms of mining and routing. Specifically, we find that any network attacker can hijack few (<100) BGP prefixes to isolate ~50% of the mining power---even when considering that mining pools are heavily multi-homed. We also show that on-path network attackers can considerably slow down block propagation by interfering with few key Bitcoin messages. We demonstrate the feasibility of each attack against the deployed Bitcoin software. We also quantify their effectiveness on the current Bitcoin topology using data collected from a Bitcoin supernode combined with BGP routing data. The potential damage to Bitcoin is worrying. By isolating parts of the network or delaying block propagation, attackers can cause a significant amount of mining power to be wasted, leading to revenue losses and enabling a wide range of exploits such as double spending. To prevent such effects in practice, we provide both short and long-term countermeasures, some of which can be deployed immediately.
Address clustering tries to construct the one-to-many mapping from entities to addresses in the Bitcoin system. Simple heuristics based on the micro-structure of transactions have proved very effective in practice. In this paper we describe the primary reasons behind this effectiveness: address reuse, avoidable merging, super-clusters with high centrality, and the incremental growth of address clusters. We quantify their impact during Bitcoin's first seven years of existence.
Ernest Mensah, Moses Aikins, Margaret Gyapong, Francis Anto · 6 authors
BACKGROUND: The global health system has a large arsenal of interventions, medical products and technologies to address current global health challenges. However, identifying the most effective and efficient strategies to deliver these resources to where they are most needed has been a challenge. Targeted and integrated interventions have been the main delivery strategies. However, the health system discourse increasingly favours integrated strategies in the context of functionally merging targeted interventions with multifunctional health care delivery systems with a focus on strengthening country health systems to deliver needed interventions. Neglected Tropical Diseases (NTD) have been identified to promote and perpetuate poverty hence there has been global effort to combat these diseases. The Neglected Tropical Diseases Programme (NTDP) in Ghana has a national programme team and office, however, it depends on the multifunctional health delivery system at the regional and district level to implement interventions. The NTDP seeks further health system integration to accelerate achievement of coverage targets. The study estimated the extent of integration of the NTDP at the national, regional and district levels to provide evidence to guide further integration. METHODOLOGY/PRINCIPAL FINDINGS: The research design was a descriptive case study that interviewed key persons involved in the programme at the three levels of the health system as well as extensive document review. Integration was assessed on two planes-across health system functions-stewardship and governance, financing, planning, service delivery, monitoring and evaluation and demand generation; and across three administrative levels of the health system-national, regional and district. A composite measure of integration designated Cumulative Integration Index (CII) with a range of 0.00-1.00 was used to estimate extent of integration at the three levels of the health system. Service delivery was most integrated while financing and planning were least integrated. Extent of integration was partial at all levels of the health system with a CII of 0.48-0.68; however it was higher at the district compared to the national and regional levels. CONCLUSIONS/SIGNIFICANCE: To ensure further integration of the NTDP, planning and finance management activities must be decentralized to involve regional and district levels of the health system. The study provides an empirical measure of extent of integration and indicators to guide further integration.
Most popular blockchain solutions, like Bitcoin, rely on proof-of-work, guaranteeing that the output of the consensus is agreed upon with high probability. However, this probability depends on the delivery of messages and that the computational power of the system is sufficiently scattered among pools of nodes in the network so that no pool can mine more blocks faster than the crowd. New approaches, like Ethereum, generalise the proof-of-work approach by letting individuals deploy their own private blockchain with high transaction throughput. As companies are starting to deploy private chains, it has become crucial to better understand the guarantees blockchains offer in such a small and controlled environment. In this paper, we present the \emph{Blockchain Anomaly}, an execution that we experienced when building our private chain at NICTA/Data61. Even though this anomaly has never been acknowledged before, it may translate into dramatic consequences for the user of blockchains. Named after the infamous Paxos anomaly, this anomaly makes dependent transactions, like "Bob sends money to Carole after he received money from Alice" impossible. This anomaly relies on the fact that existing blockchains do not ensure consensus safety deterministically: there is no way for Bob to make sure that Alice actually sent him coins without Bob using an external mechanism, like converting these coins into a fiat currency that allows him to withdraw. We also explore smart contracts as a potential alternative to transactions in order to freeze coins, and show implementations of smart contract that can suffer from the Blockchain anomaly and others that may cope with it.
This paper analyses the heterogeneity of household consumer preferences for electricity service contracts in a smart grid context. Platform pricing strategies that could incentivise consumers to participate in a two-sided electricity platform market are discussed. The research is based on original data from a discrete choice experiment on electricity service contracts that was conducted with 1,892 electricity consumers in Great Britain in 2015. We estimate a flexible mixed logit model in willingness to pay space and exploit the results in posterior analysis. The findings suggest that while consumers are willing to pay for technical support services, they are likely to demand significant compensation to share their usage and personally identifying data and to participate in automated demand response programs involving remote monitoring and control of electricity usage. Cross-subsidisation of consumers combining appropriate participation payments with sharing of bill savings could incentivise participation of the number of consumers required to provide the optimal level of demand response. We also examine the preference heterogeneity to suggest how, by targeting customers with specific characteristics, smart electricity service providers could significantly reduce their customer acquisition costs.
We examine a protocol $\pi_{\text{beacon}}$ that outputs unpredictable and publicly verifiable randomness, meaning that the output is unknown at the time that $\pi_{\text{beacon}}$ starts, yet everyone can verify that the output is close to uniform after $\pi_{\text{beacon}}$ terminates. We show that $\pi_{\text{beacon}}$ can be instantiated via Bitcoin under sensible assumptions; in particular we consider an adversary with an arbitrarily large initial budget who may not operate at a loss indefinitely. In case the adversary has an infinite budget, we provide an impossibility result that stems from the similarity between the Bitcoin model and Santha-Vazirani sources. We also give a hybrid protocol that combines trusted parties and a Bitcoin-based beacon.
The Indonesian government imposed a policy of regional autonomy with the aim to facilitate local governments regulate local affairs independently. Tangerang City is one of the areas that implement decentralization policy and requires a lot of funds to finance regional development. The biggest potential possessed Tangerang City in the financing of regional expenditures derived from local taxes and are expected to provide the largest contribution in PAD. This study aims to determine the effectiveness of tax collection hotels, restaurants, billboards and parking, and its contribution to the PAD Tangerang City. Methods of data analysis in this research is descriptive analysis. The variables in this study are the ratio of the effectiveness and contribution analysis. Data analysis technique in this study is a quantitative analysis. Based on the analysis, the average effective tax collection hotel, restaurant tax, advertisement tax and parking tax years 2010-2014 is very effective and the average contribution collection hotel, restaurant tax, advertisement tax and Tangerang city parking tax years 2010-2014 is lack.
Blockchain is essentially a set of protocols previously known as a “distributed ledger” system. An Economist article published in March 2016, describes it well: <em>Blockchain is… a database that is maintained not by a single actor, such as a bank, but collaboratively by a number of participants. Their respective computers regularly agree on how to update the database using a “consensus mechanism”, after which the modifications they have settled on are rendered unchangeable with the help of complex cryptography. Once information has been immortalised in this way, it can be used as proof of ownership.</em> The reason why this has become such a hot topic is that technologists and business people see, in these basic characteristics, immense potential for using blockchain beyond the financial services sector where it was conceived, in many different areas of the economy from energy to health, from transport to music and even as a form of digital democracy in society as a whole. The key characteristics that are attracting so much attention are the efficiencies to be derived from a network that is distributed and not centralised, combined with the permanence of the record or ledger at its heart that is cryptographically secured. This attracts those that see profound ideological implications in something that is an alternative to systems that are controlled from a single central point. For the music industry, some of these characterstics might mean that creators could, in theory, radically reduce the cost of unit transactions, thus potentially enabling content licensing for very small sums to be viable. Equally, the transparent record keeping inherent in the system has the potential to lead incrementally to the creation of a Global Repertoire Database (GRD), a kind of holy grail of the digital music industry. Some other functions that potentially could be performed on blockchain networks could relate to the establishment, validation and tracking of identities, so that individuals could be uniquely identified (e.g., as the performer on a recording). Equally good behaviour in, for example, transactions or in rights distribution speediness could contribute to developing an online reputation, which in turn could effect the sorts of terms that are made available for a particular individual or business. This paper takes a look at how bitcoin and blockchain captured the public imagination, some of the technology issues at the heart of blockchain and a key dispute that is taking the bitcoin community in different directions and has a bearing on any possible music applications. The paper explores the initially superficial ways in which blockchain represented an attractive technology and then captures some of the voices that have been generating so much deeper interest in the subject in relation to music. The paper concludes with an assessment of opportunities and obstacles.
Blockchain technology is disrupting society by enabling new kinds of disintermediated digital platforms. Furthermore, it is also providing efficiency gains on top of old existing structures by removing the need for actively intermediated data-synchronization and concurrency control. Due to this dual effect, blockchain technology has the potential to impact all sectors and layers of society, in a multitude of combined ways. While there is a lot of hype around the concept of blockchains, the phenomenon itself has remained ambiguous and misconceptions have emerged about the capabilities and the potential of blockchain technology. Drawing from ETLA’s participation in blockchain research in 2014–2016, this paper aims to provide a more comprehensive understanding on blockchain technology, its true possibilities, and its potential larger societal implications. It offers a holistic view of the key concepts and the basic principles, and the tools and the framework to understand the ongoing discussion, to critically evaluate different viewpoints, and to delve deeper in a constructed manner
Bitcoin was recently introduced as a peer-to-peer electronic currency in order to facilitate transactions outside the traditional financial system. The core of Bitcoin, the Blockchain, is the history of the transactions in the system maintained by all miners as a distributed shared register. New blocks in the Blockchain contain the last transactions in the system and are added by miners after a block mining process that consists in solving a resource consuming proof-of-work (cryptographic puzzle). The reward is a motivation for mining process but also could be an incentive for attacks such as selfish mining. In this paper we propose a solution for one of the major problems in Bitcoin : selfish mining or block-withholding attack. This attack is conducted by adversarial or selfish miners in order to either earn undue rewards or waste the computational power of honest miners. Contrary to recent solutions, our solution, ZeroBlock, prevents block-withholding using a technique free of timestamp that can be forged. Moreover, we show that our solution is compliant with nodes churn.
School Revenue and Expenditure Budget is a plan that is formulated in the form of rupiah currency and is projected for a certain period or period. In addition APBS also describes the allocation and distribution of financial resources to every part of school activities. APBS has become very popular since the enactment of decentralization policy through the implementation of school-based management (SBM). One of the decentralized authorities is autonomous management of school financial management. The formulation of the problems that I compile is how to prepare a good budget budget for financing school or madrasah in accordance with the needs; what are the school's needs for all components to be met; where are the funding sources obtained for madrasah needs; and accountability or reporting in what form is used by madrasah as responsibility in managing madrasah finance.
Abstract We formalize and construct black-box accumulation (BBA), a useful building block for numerous important user-centric protocols including loyalty systems, refund systems, and incentive systems (as, e.g., employed in participatory sensing and vehicle-to-grid scenarios). A core requirement all these systems share is a mechanism to let users collect and sum up values (call it incentives, bonus points, reputation points, etc.) issued by some other parties in a privacy-preserving way such that curious operators may not be able to link the different transactions of a user. At the same time, a group of malicious users may not be able to cheat the system by pretending to have collected a higher amount than what was actually issued to them. As a first contribution, we fully formalize the core functionality and properties of this important building block. Furthermore, we present a generic and non-interactive construction of a BBA system based on homomorphic commitments, digital signatures, and non-interactive zero-knowledge proofs of knowledge. For our construction, we formally prove security and privacy properties. Finally, we propose a concrete instantiation of our construction using Groth-Sahai commitments and proofs as well as the optimal structure-preserving signature scheme of Abe et al. and analyze its efficiency.
Irni Eliana Khairuddin, Corina Sas, Sarah Clinch, Nigel Davies
This paper presents an exploratory study focusing on user experience with Bitcoin technology. We describe interviews with 9 Bitcoin users and report findings related to users' motivations for buying and using bitcoins. Our initial findings capture three main motivations such as Bitcoin's predicted role in a monetary revolution, users' increased empowerment, and their perception of a real value of Bitcoin currency. We conclude with reflections on the value of these findings for HCI researchers.
Digital currencies represent a new method for exchange -- a payment method with no physical form, made real by the Internet. This new type of currency was created to ease online transactions and to provide greater convenience in making payments. However, a critical component of a monetary system is the people who use it. Acknowledging this, we present results of our interview study (N=20) with two groups of participants (users and non-users) about how they perceive the most popular digital currency, Bitcoin. Our results reveal: non-users mistakenly believe they are incapable of using Bitcoin, users are not well-versed in how the protocol functions, they have misconceptions about the privacy of transactions, and that Bitcoin satisfies properties of ideal payment systems as defined by our participants. Our results illustrate Bitcoin's tradeoffs, its uses, and barriers to entry.
In January 3, 2009, Satoshi Nakamoto gave rise to the "Bitcoin Block Chain" creating the first block of the chain hashing on his computers central processing unit (CPU). Since then, the hash calculations to mine Bitcoin have been getting more and more complex, and consequently the mining hardware evolved to adapt to this increasing difficulty. Three generations of mining hardware have followed the CPU's generation. They are GPU's, FPGA's and ASIC's generations. This work presents an agent based artificial market model of the Bitcoin mining process and of the Bitcoin transactions. The goal of this work is to model the economy of the mining process, starting from GPU's generation, the first with economic significance. The model reproduces some "stylized facts" found in real time price series and some core aspects of the mining business. In particular, the computational experiments performed are able to reproduce the unit root property, the fat tail phenomenon and the volatility clustering of Bitcoin price series. In addition, under proper assumptions, they are able to reproduce the price peak at the end of November 2013, its next fall in April 2014, the generation of Bitcoins, the hashing capability, the power consumption, and the mining hardware and electrical energy expenses of the Bitcoin network.
C. Lemmen, P. Knight, B. Beentjes, Jeroen van der Ham · 8 authors
Land and its administration are always negatively affected during conflicts and in post-conflict contexts.This has been confirmed both in the literature and in practice.This research has shown that if land and its administration are neglected or not properly addressed after the end of a conflict, they can be a cause for a renewed armed conflict and an obstacle in the rebuilding of a post-conflict society.The author's initial research on the topic revealed that there is a relation between land administration and post-conflict state building.Therefore, the main research objective was to identify which interventions in land administration and under which circumstances facilitate postconflict state building.In order to achieve the main research objective, a qualitative research approach with a fieldwork was applied on two main case studies: Kosovo and Rwanda.Findings from the main case studies were supported with three supportive case studies: Mozambique, Cambodia and Timor-Leste, by collecting data from the literature.Empirical data and literature were used to set the theoretical propositions as: (1) a framework for rebuilding post-conflict states, and (2) interventions in land administration for post-conflict state building.For the final discussions and for the analytical generalisation correlating analyses were performed in a three-dimensional matrix, where the theoretical propositions (1) and (2) formed a skeleton of the matrix and empirical data from the main case studies constitutes the third dimension.The research first derived general findings on land, conflict and post-conflict contexts and, finally, specific findings were presented as in the framework for rebuilding post-conflict states grouped as: institutional weaknesses, economic and social problems, and serious security problems.Main findings from this research lead to conclusion that the identified interventions in land administration can be seen as facilitators of post-conflict state building.
The growing use of computers in modern control systems has led to the develop- ment of complex dynamic systems known as hybrid systems, which integrates both discrete and continuous systems. Given that hybrid systems are systems that operates in real time allowing for changes in continuous state over time periods, and discrete state changes across zero time, their modelling, analysis and verification becomes very difficult. The formal verifications of such systems based on specifications that can guar- antee their behaviour is very important especially as it pertains to safety critical applications. Accordingly, addressing such verifications issues are important and is the focus of this thesis. In this thesis, in order to actualise the specification and verification of hybrid systems, Interval Temporal Logic(ITL) was adopted as the underlying formalism given its inherent characteristics of providing methods that are flexible for both propositional and first-order reasoning regarding periods found in hardware and software system’s descriptions. Given that an interval specifies the behaviour of a system, specifications of such systems are therefore represented as a set of intervals that can be used to gain an understanding of the possible behaviour of the system in terms of its composition whether in sequential or parallel form. ITL is a powerful tool that can handle both forms of composition given that it offers very strong and extensive proof and specifi- cation techniques to decipher essential system properties including safety, liveliness and time projections.However, a limitation of ITL is that the intervals within its framework are considered to be a sequence of discrete states. Against this back- drop, the current research provides an extension to ITL with the view to deal with verification and other related issues that centres around hybrid systems. The novelty within this new proposition is new logic termed SPLINE Interval Temporal Logic (SPITL) in which not only a discrete behaviour can be expressed, but also a continuous behaviour can be represented in the form of a spline i.e. the interval is considered to be a sequence of continuous phases instead of a sequence of discrete states. The syntax and semantics of the newly developed SPITL are provided in this thesis and the new extension of the interval temporal logic using a hybrid system as a case study. The overall framework adopted for the overall struc- ture of SPITL is based on three fundamental steps namely the formal specification of hybrid systems is expressed in SPLINE Interval Temporal Logic, followed by the executable subset of ITL, called Tempura, which is used to develop and test a hybrid system specification that is written in SPITL and finally a runtime verification tool for ITL called AnaTempura which is linked with Matlab in order to use them as an integrated tool for the verification of hybrid systems specification. Overall, the current work contributes to the growing body of knowledge in hybrid systems based on the following three major milestones namely: i. the proposition of a new logic termed SPITL; ii. executable subset, Tempura, integrated with SPITL specification for hybrid systems; and iii. the development of a tool termed Ana Tempura which is integrated with Matlab to ensure accurate runtime verification of results.
An internal model based method is used to estimate the structural displacements under ambient excitation using only acceleration measurements. Strain measurements are incorporated to expand the method to single span concrete bridges subjected to moving vehicle loads. The structural response is assumed to remain the linear range for the duration of the loading. The excitation is assumed to be with zero mean and relatively broad bandwidth such that at least one of the fundamental modes of the structure is excited and dominates in the response. Using the structural modal parameters and partial knowledge of the load, their respective internal models can be established. These internal models can then be used to form an autonomous state-space representation of the system. It is shown that structural displacements, velocities, and accelerations are the states of such a system, and it is fully observable when the measured output contains structural accelerations only. Reliable estimates of structural displacements are obtained using the standard Kalman filtering technique. These displacement estimates can be used to determine the moment demand and provide insight into whether this demand is exceeding the capacity of the bridge. The effectiveness and robustness of the proposed method has been demonstrated and evaluated via numerical simulations of an eight-story lumped mass model along with a simply supported single span concrete bridge subjected to a moving traffic load. Experimental data of a three-story frame excited by ground accelerations from an actual earthquake record is also used. Lastly, field data from an inverted arch concrete bridge is analyzed as proof of concept for deployment of a structural health monitoring system for the purpose of displacement estimations.
The Internet of Things and Services (IoTS) has encouraged the development of service provisioning systems in respect to Smart City topics. Most of them are operated as heterogeneous systems which limits end customers’ access and contradicts with IoTS principles. In this paper, we discuss and develop a reference model of an interconnected service marketplace ecosystem. The prototypical implementation incorporates findings from an empirical study and lessons learned from research projects. The elaborated ecosystem enables service request roaming between different parties across system boundaries. The paper presents a feasible centralized architecture, introduces involved parties and parts of a developed message protocol. Why a contracting mechanism is indispensable for request roaming is also outlined. The model’s feasibility is demonstrated by means of a current electric mobility use case: providing access to foreign charging infrastructure without multiple registrations. This work contributes to simplify the data exchange between service platforms to improve Smart City solutions and to support travelers with intelligent mobility applications.
This dissertation addresses the assembly of organizational resources by technology ventures. We study how innovative firms acquire human and financial capital and then organize those resources, and how public policy affects that capability.\nIn the first chapter, we study the role of information in organizational decision-making for the financing of entrepreneurial ventures. We formally model a decentralized set of agents who vote strategically to allocate resources to a project with unknown outcome; they can each acquire costly information to improve their decision quality. We test our predictions in the setting of venture capital, where partners make their own angel investments outside of their employer. We find that the venture capital partners, acting independently, make riskier investments into younger firms with less educated and younger founding teams, but these investments perform better on some metrics even when controlling for investment size and stage. Geographic distance and liquidity constraints increase the probability the investment is taken up by a partner and not the VC.\nIn the second chapter, we evaluate the impact of skilled immigration on U.S. innovation by exploiting a random lottery in the H-1B visa program. Proponents argue that immigration allows firms to access technical skills and promote innovation, while opponents argue that firms substitute domestic labor for cheaper but equally or less skilled foreign labor. We find that winning an H-1B immigrant does not significantly increase patent applications or grants at the firm level, and there is pervasive use of the program in industries where patenting is not the main value-appropriation strategy.\nIn the third chapter, we study how a firm should organize the diversity of technical experience, contained within its pool of inventive human capital, for firm-level innovation. Using a sample of biotechnology start-ups, we examine the implications of alternate firm-level design regimes, drawing on both a firm-year panel structure and an inventor-year difference-in-differences empirical approach. Organizing a firm's human capital with greater across-team diversity yields increased firm-level innovation benefits as compared to organizing with greater within-team diversity. The benefits of across-team diversity stem mainly from the influence of that regime on team stability.
This Study investigates time-series change of employment centers by nine industries between 2000 and 2010. The study discusses different distribution pattern of employment centers of Seoul Metropolitan Area (SMA) by industries. The spatial concentration level is calculated by Global Moran’s I and Local Moran’s I. The results are summarized as follows. First, overall employment distribution change shows decentralization. High density areas were connected to the traditional employment centers and made employment corridor. Second, basic industries like manufacturing and transportation had moved from the old business centers to outskirts. Third, public services including education and human health and social work activities have been relatively well distributed and showed minor change during the study period. Fourth, finance and insurance and real estate activities are clustered in the 3 major centers. The results imply that employment distribution analysis by major industries are necessary as well as total employment distribution in order to improve efficiency of urban spatial structure. For instance, if we can assume the different housing demand by industries, employees of manufacturing companies need to move to near suburban areas while residential buildings for FIRE industries are planned in the traditional business centers.