Bitcoin is a peer-to-peer payment system proposed by Nakamoto in 2008. Based on the Nakamoto consensus, Bagaria, Kannan, Tse, Fanti, and Viswanath proposed the Prism protocol in 2018 and showed that it achieves near-optimal blockchain throughput while maintaining a similar level of security as bitcoin. Previous probabilistic security guarantees for the bitcoin and Prism backbone protocols were either established under a simplified discrete-time model or expressed in terms of exponential order results. This paper presents a streamlined and strengthened analysis under a more realistic continuous-time model. A fully rigorous model for blockchains is developed with no restrictions on adversarial miners except for an upper bound on their aggregate mining rate. The only assumption on the peer-to-peer network is that all block propagation delays are upper bounded by a constant. A new notion of "t-credible blockchains" is introduced, which, together with some carefully defined "typical" events concerning block production over time intervals, is crucial to establish probabilisitic security guarantees in continuous time. A blockchain growth theorem, a blockchain quality theorem, and a common prefix theorem are established with explicit probability bounds. Moreover, under a certain typical event which occurs with probability close to $1$, a valid transaction that is deep enough in one credible blockchain is shown to be permanent in the sense that it must be found in} in all future credible blockchains.
We report on the use of sentiment analysis on news and social media to analyze and predict the price of Bitcoin. Bitcoin is the leading cryptocurrency and has the highest market capitalization among digital currencies. Predicting Bitcoin values may help understand and predict potential market movement and future growth of the technology. Unlike (mostly) repeating phenomena like weather, cryptocurrency values do not follow a repeating pattern and mere past value of Bitcoin does not reveal any secret of future Bitcoin value. Humans follow general sentiments and technical analysis to invest in the market. Hence considering people's sentiment can give a good degree of prediction. We focus on using social sentiment as a feature to predict future Bitcoin value, and in particular, consider Google News and Reddit posts. We find that social sentiment gives a good estimate of how future Bitcoin values may move. We achieve the lowest test RMSE of 434.87 using an LSTM that takes as inputs the historical price of various cryptocurrencies, the sentiment of news articles and the sentiment of Reddit posts.
Traditional Blockchain Sharding approaches can only tolerate up to n/3 of nodes being adversary because they rely on the hyper-geometric distribution to make a failure (an adversary does not have n/3 of nodes globally but can manipulate the consensus of a Shard) hard to happen. The system must maintain a large Shard size (the number of nodes inside a Shard) to sustain the low failure probability so that only a small number of Shards may exist. In this paper, we present a new approach of Blockchain Sharding that can withstand up to n/2 of nodes being bad. We categorise the nodes into different classes, and every Shard has a fixed number of nodes from different classes. We prove that this design is much more secure than the traditional models (only have one class) and the Shard size can be reduced significantly. In this way, many more Shards can exist, and the transaction throughput can be largely increased. The improved Blockchain Sharding approach is promising to serve as the foundation for decentralised autonomous organisations and decentralised database.
As the first decentralized peer-to-peer (P2P) cryptocurrency system allowing people to trade with pseudonymous addresses, Bitcoin has become increasingly popular in recent years. However, the P2P and pseudonymous nature of Bitcoin make transactions on this platform very difficult to track, thus triggering the emergence of various illegal activities in the Bitcoin ecosystem. Particularly,mixing servicesin Bitcoin, originally designed to enhance transaction anonymity, have been widely employed for money laundering to complicate the process of trailing illicit fund. In this article, we focus on the detection of the addresses belonging to mixing services, which is an important task for anti-money laundering in Bitcoin. Specifically, we provide a feature-based network analysis framework to identify statistical properties of mixing services from three levels, namely, network level, account level, and transaction level. To better characterize the transaction patterns of different types of addresses, we propose the concept of attributed temporal heterogeneous motifs (ATH motifs). Moreover, to deal with the issue of imperfect labeling, we tackle the mixing detection task as a positive and unlabeled learning (PU learning) problem and build a detection model by leveraging the considered features. Experiments on real Bitcoin datasets demonstrate the effectiveness of our detection model and the importance of hybrid motifs including ATH motifs in mixing detection.
We improve the fundamental security threshold of eventual consensus Proof-of-Stake (PoS) blockchain protocols under the longest-chain rule by showing, for the first time, the positive effect of rounds with concurrent honest leaders. Current security analyses reduce consistency to the dynamics of an abstract, round-based block creation process that is determined by three events associated with a round: (i) event $A$: at least one adversarial leader, (ii) event $S$: a single honest leader, and (iii) event $M$: multiple, but honest, leaders. We present an asymptotically optimal consistency analysis assuming that an honest round is more likely than an adversarial round (i.e., $\Pr[S] + \Pr[M] > \Pr[A]$); this threshold is optimal. This is a first in the literature and can be applied to both the simple synchronous communication as well as communication with bounded delays. In all existing consistency analyses, event $M$ is either penalized or treated neutrally. Specifically, the consistency analyses in Ouroboros Praos (Eurocrypt 2018) and Genesis (CCS 2018) assume that $\Pr[S] - \Pr[M] > \Pr[A]$; the analyses in Sleepy Consensus (Asiacrypt 2017) and Snow White (Fin. Crypto 2019) assume that $\Pr[S] > \Pr[A]$. Moreover, all existing analyses completely break down when $\Pr[S] < \Pr[A]$. These thresholds determine the critical trade-off between the honest majority, network delays, and consistency error. Our new results can be directly applied to improve the security guarantees of the existing protocols. We also provide an efficient algorithm to explicitly calculate these error probabilities in the synchronous setting. Furthermore, we complement these results by analyzing the setting where $S$ is rare, even allowing $\Pr[S] = 0$, under the added assumption that honest players adopt a consistent chain selection rule.
With the integration of highly permeable renewable energy to the grid at different levels (transmission, distribution and grid-connected), the volatility on both sides (source side and load side) leading to bidirectional power flow in the power grid complicates the control mechanism. In order to ensure the real-time power balance, energy exchange, higher energy utilization efficiency and stability maintenance in the electric power system, this paper proposes an integrated application of blockchain technology on energy routers at transmission and distribution networks with increased renewable energy penetration. This paper focuses on the safe and stable operation of a highly penetrated renewable energy grid-connected power system and its operation. It also demonstrates a blockchain-based negotiation model with weakly centralized scenarios for “source-network-load” collaborative scheduling operations; secondly, the QoS (quality of service) index of energy flow control and energy router node doubly-fed stability control model were designed. Further, it also introduces the MOPSO (multi-objective particle swarm optimization) algorithm for power output optimization of multienergy power generation; Thirdly, based on the blockchain underlying architecture and load prediction value constraints, this paper puts forward the optimization mechanism and control flow of autonomous energy coordination of b2u (bottom-up) between router nodes of transmission and distribution network based on blockchain.
Electronic Health Records (EHRs) have improved many aspects of healthcare and allowed for easier patient management for medical providers. Blockchains have been proposed as a promising solution for supporting Electronic Health Records (EHRs), but have also been linked to scalability concerns about supporting real-world healthcare systems. This paper quantifies the scalability issues and bottlenecks related to current blockchains and puts into perspective the limitations blockchains have with supporting healthcare systems. Particularly we show that well known blockchains such as Bitcoin, Ethereum, and IOTA cannot support transactions of a large scale hospital system such as the University of Kentucky HealthCare system and leave over 7.5M unsealed transactions per day. We then discuss how bottlenecks of blockchains can be relieved with sidechains, enabling well-known blockchains to support even larger hospital systems of over 30M transactions per day. We then introduce the Patient-Healthchain architecture to provide future direction on how scaling blockchains for EHR systems with sidechains can be achieved.
The Lightning Network (LN) was released on Bitcoin's mainnet in January 2018 as a solution to favor scalability. This work analyses the evolution of the LN during its first year of existence in order to assess its impact over some of the core fundamentals of Bitcoin, such as: node centralization, resilience against attacks and disruptions, anonymity of users, autonomous coordination of its members. Using a network theory approach, we find that the LN represents a centralized configuration with few highly active nodes playing as hubs in that system. We show that the removal of these central nodes is likely to generate a remarkable drop in the LN's efficiency, while the network appears robust to random disruptions. In addition, we observe that improvements in efficiency during the sample period are primarily due to the increase in the capacity installed on the channels, while nodes' synchronization does not emerge as a distinctive feature of the LN. Finally, the analysis of the structure of the network suggests a good preservation of nodes' identity against attackers with prior knowledge about topological characteristics of their targets, but also that LN is probably weak against attackers that are within the system.
Insurance is one of the fundamental services offered to the citizens to reduce their costs and assist them in case of an emergency. One of the most important challenges in the insurance industry is to address liability challenge and the forging of documents by the involved parties, i.e., insurance company or the users, in order to increase financial gain. Conventional methods to address this challenge is significantly time consuming and costly and also suffers from lock of transparency. In this paper, we propose a blockchain-based solution for the insurance industry in smart cities (BIS). BIS creates a big umbrella that consists of the smart city managers, insurance companies, users, and sensors and devices. The users are known by changeable Public Keys (PKs) that introduces a level of anonymity. The data collected by the sensors is stored in cloud or local storage and is shared with insurance company on demand to find the liable party that in turn increases the privacy of the users. BIS enables the users to prove and share the history of their insurances with other users or insurances. Using Proof of Concept (POC) implementation we demonstrated the applicability of blockchain in insurance industry. The implementation results prove that BIS significantly reduces delay involved in insurance industry as compared with conventional insurance methods.
The above article from Journal of Forecasting, published online on 14 January 2020 in Wiley Online Library (http://wileyonlinelibrary.com) as an 'Accepted Article' (https://onlinelibrary.wiley.com/doi/epdf/10.1002/for.2656) has been withdrawn by agreement among the author, the Journal Editor-in-Chief (Professor Derek Bunn) and John Wiley & Sons Ltd. This action has been agreed because after acceptance but before final publication, the author requested to withdraw this manuscript as they wished to revise the manuscript further before the publication of the Version of Record.
In 2011 and the ensuing years, the world witnessed a global wave of various “occupy movements,” from the Spanish 15-M and the Greek anti-austerity protests of 2011 to Occupy Wall Street (OWS), and from the Gezi Park protests in Istanbul to Nuit Debout in Paris. Inspired by the Arab Spring earlier that year—and by the iconic image of an occupied Tahrir Square in particular—protesters in different parts of the world took possession of public spaces in order to oppose the austerity measures of their governments, to challenge the power of financial industries and economic elites, and to voice their widely shared experience of a democratic deficit. I emphasize from the outset that there are many, and often very substantial, demographic, cultural, economic, and political differences among these various occupy movements and among the contexts in which they intervened. There is thus no particular reason to assume, as some enthusiastic commentators suggested at the time, that they were all exponents of a single global movement (Hardt & Negri, 2012; Mason, 2011). But it is also clear, on the other hand, that they often expressed a strong sense of solidarity with each other, and referred to each another as important sources of inspiration (Graeber, 2013, p. 237). Notwithstanding the many differences between these movements, they did share at least a number of important points in common. What, then, did these movements have in common—next to the obvious but important fact that they all involved the occupation of public space (Harvey, 2012, pp. 161–162)? First, in most cases conventional political organizations or institutions played a minor role, if any, in these mass mobilizations. None was spearheaded by established political parties or politicians (Tormey, 2015, p. 8) and they often had a strikingly diverse composition (Juris, 2012, p. 265). Most categorically refused to negotiate or even engage with any representative institutions or public bodies (Klein, 2011). One possible explanation for this, second, is that many of these movements had strong horizontalist aspirations (Sitrin, 2012) and advocated direct or participatory forms of politics, organization and decision-making. Finally, not only did they propose an alternative view of democracy, but they also put it in practice: a significant aspect of their shared repertoire was that these movements sought to prefigure a radical form of democracy (Bray, 2013, p. 190; Douzinas, 2013, pp. 158–160; Hardt & Negri, 2017, pp. 274–275; Maeckelbergh, 2016; Pickerill & Krinsky, 2012; Smucker, 2014; Van de Sande, 2013; Yates, 2015). By organizing in general assemblies and spokes-councils, for example, they tried to realize, in the here and now, the kind of radical social change that they aspired to bring about on the long term (Graeber, 2013). These movements’ refusal to engage with existing parties and institutions, their horizontalist or direct democratic aspirations, and their attempt to prefigure these ideals in their general assemblies and consensual decision-making procedures, have all contributed to the widespread idea that they were opposed to any form of political representation. Indeed, many prominent political philosophers and social movement theorists have promoted this view of recent occupy movements. My claim, however, is that this reading is too quick. Not only is it far from certain that all these movements dismissed political representation tout court, but upon closer inspection it becomes clear that both in their rhetoric and practical organization they employed various forms of representation and of making representative claims. In fact, these movements also played a significant representative on their own part, which remains undertheorized in the current debate. What concepts of representation are implied here? And what lessons for democracy, strategy, and social movement politics may we derive from them? To answer these questions and to shift the academic debate on these occupy movements, I reconstruct two concepts of representation that can be encountered in the practices and rhetoric of occupy movements such as OWS and the 15-M movement. I focus on one concept of representation in particular that I think is the key to an adequate understanding of contemporary social movements, but that is not sufficiently theorized in the existing literature on these movements: namely, the idea of synecdochal representation, where one of the constituent parts stands for a larger whole. To address these questions I make the following argumentative steps. In Section 2, I briefly review the contemporary academic debate on occupy movements and their relation to political representation. Should the statements and practices of movements such as OWS indeed be regarded as a rejection of representation, as both their critics and advocates claim, or is their repertoire with at least some forms of In Section I to the academic literature on political representation and it is far from obvious what representation from on representation, I two different of representation, which are both representation as on the one hand, and representation as or larger on the In Section I these to the politics of recent occupy movements, and both are as as in their practices and In Section I the concept of representation as on a particular form of representation that I think is the key to understanding of recent occupy movements and their representative role, but that remains undertheorized in the current namely, synecdochal representation. I to the of employed this concept at various in but a of concept of synecdochal representation and political I it in the of recent occupy movements in Section the of the occupy movements in 2011 and the following years, their and the among and is to these movements or their and or to their of representative democracy in current My is if we are to and this and political we to a and of representation and the political that it may the of movements as Occupy Wall Street is an in we can no make as we for change in the power and we can no to their we are a of what democracy this to one another to is a to and the that direct we the power p. many of the statements and by these occupy movements, is to various to many political philosophers and social movement it that OWS representative to the image of democracy a direct or participatory form of democracy, which is with representative democracy in current One may to this that the for a radical or participatory form of democracy was expressed even in their to prefigure such in 2013, p. p. with consensual decision-making and forms of public (Bray, 2013; 2012; and alternative also to their own to in the occupy with of 2015, p. and pp. & 2013). In these movements tried to their of a democratic in the here and de Sande, 2013, p. is what democracy another prominent by these occupy movements, thus can be referred to the forms and practices that these movements the as OWS it in their their occupied as a in all the it in the and even are not as of political but as of a general rejection of the of representation. & p. here is that representative democracy is an categorically the from in the political (Hardt & Negri, pp. p. democracy, on the other hand, a horizontalist of organization and a rejection of democracy and the of that such of (Sitrin, 2012, p. also Mason, p. horizontalist or that the occupy movements expressed in both their practices and rhetoric is thus not in with political the two are this is shared by some of these movements’ most prominent for example, that their to engage with any representative institutions or a of the as a of a of and by pp. a their horizontalist aspirations a understanding of in general p. also pp. that a democracy political are the of and representative p. What these movements to is the fact that are no to the representative institutions and I with these critics that it is and to democratic on a rejection of all representative p. I not think that recent occupy movements such as OWS and the categorically any form of political I that their political repertoire was of making all forms of representative claims. are we to make sense of these movements’ practices and such as are the is what democracy or even at least some concept of political representation 2015, p. In the of this I a concepts of representation that I think are to these movements. But briefly on the various and of What is we at the term is employed both in academic and political it may that it and in of these various of the term representation are but their and are very p. these various two different that can be as a to that in other p. 2013, pp. pp. In and for example, representation may be as or What is in this is the particular relation in which a particular representative it a a or a or even in to this form of representation as idea of or the idea of of or in the and the idea of as a on in with the of p. representation as for an this is not the in any a certain of is to as the of political representation on the of a representative and to the or of a particular or that both and at a certain from the In the of representative as a representative be to one the other p. concept of representation is for in understanding of representative all the also have a term as or is in the in for a or or a of can be to other or larger to such forms of representation as not a or a it to what a representative an understanding of what a representative it a an or a it be to p. Spanish or were the in many recent occupy to this representation, and to both concepts of both as for and in the academic debate on political representation the two to be both at a and a practical there are important to a between these forms of representation. the most significant between representation as for and representation as for is that the often an and a certain of between the representative and the In the of the thus be the is to the as in the on the other hand, a often to to make it by their it is not in p. is a is to not to an that be or bring that did not as to is not a of to or to what it stands and what to a be as to as p. of in other is a that also the of certain or that which is in a relation of representation not this relation as There is no or the particular or that representation as for that there is an and can be in a or representation as a for that the not it is the of a representative or relation pp. the political of representation as for is that representation as for is of no political theorists of political representation, such as and have that representation as for an important in the of political and p. that making of or of what is to be is a aspect of political By a particular image of or what they to this or not that this no is a But the political in the of making of p. representation as for is an pp. p. any representative is of own in that it be in a particular in it and the other the of and from such of as for thus can be as a of & p. is a political one may there is a between various possible To one or be at the of to put it in and any representation to is to the of to the of to a & p. then, did the practices of recent occupy movements such as the and OWS indeed of any form of political many of their advocates and critics And if can these various forms of political representation as for and for be in their rhetoric and we have the of recent occupy movements is often as of a of political representation tout & p. Hardt & Negri, 2012, pp. 2013, pp. 2015, p. is clear that these movements were of representative democracy in current But that we have between different forms of political representation, we may their politics indeed a rejection of all forms of One important of the politics of these occupy movements, to is that both in their rhetoric and practices they sought to representative democracy with a direct or of general forms of and horizontalist decision-making are to a of what democracy be (Graeber, 2013, p. may that these movements were at least very of representation as idea that some may be to and in But if we at both their rhetoric and their these movements to have a understanding of representation as for example, the OWS at the of Section this a between democracy and representative democracy as we it it also for their to the p. the that there are to for or on of the in a or sufficiently democratic OWS a for in this in of the OWS p. that both political parties in the the we the are of the it that these occupy movements often employed various forms of political representation in example, a the occupation of general was as the most important of decision-making by a (Bray, 2013). be by from each was among the of each and each had a to voice only the (Graeber, 2013, p. to these were not in the sense they the of the (Bray, 2013, p. But it be to that or an is a form of representation as for that an and a very of forms of representation are by no with organization or even decision-making. and radical democratic theorists have that radical democracy various forms of or 2015, p. pp. p. pp. the of forms of very to the of and 2012, p. 2014; Smucker, 2017, pp. is not such can be to an but they can be and These movements’ with and participatory forms of organization may have to a different idea of democracy, but this a of representation as What is many of these movements’ have to engage with conventional forms of politics their had to an One obvious is the Spanish which in the of the 15-M movement and had at both the and the & pp. and this to an was no a 2015, pp. is that even some involved with the 15-M movement have to an particular at the In the Spanish for example, took in the of a public which in the of & as as (Graeber, also pp. are representative in the is to of political to of and thus a direct 2017, p. widespread that the politics of these movements the very of representation thus to be & p. closer inspection it that many forms of representation as for were employed by these movements. that their radical democratic practices and be as a for and direct and participatory representation to the current of the 2017, p. there is also a to be not only did these movements’ and organization certain forms of representation as but in some they also an important representative in their own such as OWS and the did not or to any or to or make on of a larger of But they did as political in at least some To this, however, we to to the second, concept of representation that I namely, representation as or politics of a social movement any form of representation is and an important not only a or to the but also derive a sense of and from the most may any form of representation, not that their own or their stands for recent occupy movements were no to to the OWS the is of representative democracy in current But the also that the p. And this the in political least that the this stands for a and not in the of in Park 2015, p. can be of other prominent movement such as are the and a strong representative that to a larger of and not to are at the of 2015, p. practices of these occupy movements implied a representative the general alternative decision-making and all for My claim, is that the particular form of political representation, is in the and rhetoric of these occupy movements. representation as this form of representation is not with their radical democratic aspirations or as many social movement theorists and political philosophers In fact, I that it is it is implied in their direct democratic In the of this I to a particular concept of representation as for that is at namely, a synecdochal concept of representation. I this particular form of representation is key to an understanding of the recent occupy movements. as for a representation as of or of all other or larger as this form of representation also a political is of in the of representation as for is a where a representative to or and on of the representation as for is a a movement from to and a one from representative to p. also p. is also a political in order to any and thus at the of & pp. of political representation, often to this concept of representation as a for 2013, p. In of political representation, on the image of the a form of that other such as and the differences between and to are established & p. this of an in of representation p. a of the to this are this concept can be to the representative and practices of recent occupy movements, we thus to reconstruct the often of the in of representation. But what the it is from other of such as the and the and it is in a of political representation. may be regarded as a of 2015, p. we by between and the is on or the of a example, in radical it is to to as is a the in not to relation between and is on or of their of this is or is is that are In on the other hand, the relation between the and the be by a particular are Wall Street or the as to the financial or to a particular of the In both cases there is a direct and relation between is as the of financial the in the but the term as a not this a relation in that it is on a But there is one in a synecdochal relation the is a of the larger that it a such as have to or the of as a to are of a and are a of their an to the between and p. are on But this also that representation can be established only as a or relation p. it is on many different can be to a single To to the many not from the may be to the of There is no particular reason the between the and to such an established in and have the But the fact is in order to as a had to these other possible and thus had to as the only or most for the to be it is one among many is very different for the as we have is on a that as a in a relation is to the that it and the relation between thus for with a of politics what the or can be in to the the of a not on to other possible it remains a far as is however, this also that the only a for and In a of a particular representation of upon the of as a representation of as a whole. own and an p. and of a social that remains an pp. with however, is that they are on one of many possible and that the of one relation not at the of we was the with thus the that is to a political representation pp. To a to some of p. p. is where the of the becomes a particular to this de the as of the that an between and p. p. from this the is not a of the it a between these other in that it a relation between and that is particular that upon the p. to or for a larger is the only that this p. & p. to as a synecdochal on to be as the only at the most obvious and representation. synecdochal representation the of a pp. an image of the for by a concept of the that be or even possible p. but that as the of this and thus to it as far as is this is the of the forms the for understanding of political it one representative or relation can a larger at the time, it p. 2015, pp. these and not as are as two different of this in a have a particular shared or can be and in own they a their p. their is by the long as this remains an it not to a But that this is only one among many different claims. that of other or have also this may to the of a social their shared experience of or their with the in and a sense of which is by a shared understanding or of the which as p. of a social not only these but to a different of their to the of a larger of in which all the in of their to what we an p. Notwithstanding the differences between these and their particular or their shared experience of and their the of a social to a or between these various and of however, to in a particular a of these various not be representation of an only possible if a particular own also as a the as a p. also pp. By of public or for example, one particular to the thus for a of or First, the of the two of and a certain between is the of the in this they to be the of at a and a of in the of a the term becomes the of a it no the of an be in all and becomes the of a social only is the of that in a pp. What we is a particular or to for a at the in to What this however, is that the of a also the of or claims. here not only the or of an but a a particular of or other and and a view of these be In it to for a political then, can concept of synecdochal representation to the politics of recent occupation is far from obvious to in this both p. and have these movements for their refusal to engage with representative My claim, however, is that their be employed in an of these very movements and their practices & p. In the I a of these movements established such synecdochal both and have of occupy movements such as OWS and the Spanish 15-M I that their can be employed to a understanding of these movements and their political repertoire p. concept of the in can to the forms of political representation that were implied in these movements’ practices and a on example, of is that of are the was by in in which that only of a of the and that it of the on contributed to the of the idea that be between a and a (Graeber, 2013, p. this of from the of by a that their of or and were all by the the these were all of many different and the suggested that all these had important in common. in a single or all the all the this idea of the that they a the I in the also suggested a representative is representative for what we all are of the obvious differences between In this the and the idea of a what and an between various and on the of a and experience that they all to have in common. shared which be in of or to a of and thus to a p. is the of occupation in these movements’ One shared by many of these movements is that the public in the sense of a and in the sense of a public In all parts of the world public spaces and are and this in many to the of an and concept of occupation of public space was not a but in one or the other, the occupied space was also often at 2015, p. it is no that the occupation of space played such an important for various movements the which all space as public occupied what is and the of to and as a 2015, p. Gezi Park was occupied in of the to to the of and of to another example, is not only only a from Wall but it is also a public space that the of this is a widespread and the occupation of a single very to the the of public But it a of the of public space in of in and to a for as a in for a whole. In this the that stands for is a on the one hand, on the other, a with the 2012, p. a that direct democratic decision-making and horizontalist were to a or at the very least a of and what a be (Graeber, 2013, p. also p. pp. not that these movements or to direct democratic decision-making we have their repertoire often various forms of representation as But the is by with alternative forms of organization and these movements did to their for a participatory and form of democracy we have in general and other by these movements, a larger of and is not that the synecdochal form of representation as an for these practices larger p. of their of representative democracy in current the practices of movements are In other the in which their practices and for a social or or occupation of public the of decision-making and the of a synecdochal they were representative and such as is what democracy are the or these with a particular synecdochal and is the of these statements that these to for larger a particular concept of democracy, a of the or the What is the and of political representation in the repertoire of occupy movements, such as OWS and the 15-M the of these movements in 2011 this a of debate among political theorists and social movement advocates and critics of these movements have that their horizontalist aspirations, their radical democratic rhetoric and their all a rejection of political representation I if we to these movements’ of political representation we be to various and representation as for on the one hand, and representation as for on the often an and some of between the representative and the as on the other hand, is a form of representation in which the a particular the of representation. I that both forms of representation were in fact employed by these occupy movements: representation as for can be encountered in their of and as on the other hand, can be in the these movements a idea of they for and what they aspired to in the of such synecdochal can be in their practices on the one occupation of public the general in their rhetoric and is what democracy are the the to these movements’ and practices as of political representation is the these to that representation as for not any the of representative be and And a synecdochal form of representation, in which a to for a larger sufficiently to and may it or even forms of Finally, if the politics of recent occupy movements indeed of many forms of political representation, their of representative democracy in current be To if not a direct or participatory form of democracy, did these movements their and practices indeed as a for and direct and participatory 2017, p. what this alternative view of democracy in the of these movements, many of these questions to be One a of these however, is that we the that various forms of representation played in these movements’ politics and we be to lessons from their on the of democracy and social movement de is in at are radical democratic political representation, and contemporary movements.
Víctor Gayoso Martínez, Luis Hernández–Álvarez, Luis Hernández Encinas
Blockchain is one of the most interesting emerging technologies nowadays, with applications ranging from cryptocurrencies to smart contracts. This paper presents a review of the cryptographic tools necessary to understand the fundamentals of this technology and the foundations of its security. Among other elements, hash functions, digital signatures, elliptic curves, and Merkle trees are reviewed in the scope of their usage as building blocks of this technology.
Ethereum is one of the most popular blockchain systems that supports more than half a million transactions every day and fosters miscellaneous decentralized applications with its Turing-complete smart contract machine. Whereas it remains mysterious what the transaction pattern of Ethereum is and how it evolves over time. In this paper, we study the evolutionary behavior of Ethereum transactions from a temporal graph point of view. We first develop a data analytics platform to collect external transactions associated with users as well as internal transactions initiated by smart contracts. Three types of temporal graphs, user-to-user, contract-to-contract and user-contract graphs, are constructed according to trading relationship and are segmented with an appropriate time window. We observe a strong correlation between the size of user-to-user transaction graph and the average Ether price in a time window, while no evidence of such linkage is shown at the average degree, average edge weights and average triplet closure duration. The macroscopic and microscopic burstiness of Ethereum transactions is validated. We analyze the Gini indexes of the transaction graphs and the user wealth in which Ethereum is found to be very unfair since the very beginning, in a sense, "the rich is already very rich".
Mohammed Amine Bouras, Qinghua Lu, Zhang Fan, Yueliang Wan · 6 authors
Electronic healthcare (eHealth) identity management (IdM) is a pivotal feature in the eHealth system. Distributed ledger technology (DLT) is an emerging technology that can achieve agreements of transactional data states in a decentralized way. Building identity management systems using Blockchain can enable patients to fully control their own identity and provide increased confidence in data immutability and availability. This paper presents the state of the art of decentralized identity management using Blockchain and highlights the possible opportunities for adopting the decentralized identity management approaches for future health identity systems. First, we summarize eHealth identity management scenarios. Furthermore, we investigate the existing decentralized identity management solutions and present decentralized identity models. In addition, we discuss the current decentralized identity projects and identify new challenges based on the existing solutions and the limitations when applying it to healthcare as a particular use case.
The information systems of decentralized organizations are now networked as components of a global information system. Organizations, individuals and software act autonomously and are at the same time cooperatively involved in the creation of services. The planning and execution of the necessary interactions in the form of processes are not under the control of individuals. For the development and execution of processes under decentralized coordination, this work proposes an approach based on blockchain technologies. This addresses, on the one hand, the design of decentralized organizations and, on the other hand, the coordination of development that is distributed within such systems and is not centrally controlled. The thesis describes the decentralization and the model-based development of process-oriented systems from an organizational theory perspective. The focus is then on decentralized blockchain systems as development and execution platforms, with which the binding nature and integrity of transactions between a priori unknown nodes of a network can be guaranteed. The development and execution of processes are implemented on this basis using a model-based approach. This is established by an architectural framework for conceptual modeling, for cooperative modeling and for the tracking of instances. The conceptual modeling of networks, processes and instances makes use of the semantic object model (SOM) in order to map the task level of decentralized organizations to a decentralized task management level. The cooperative modeling and the tracking of instances use technologies for distributed version management in connection with smart contracts of the blockchain system Ethereum. The demonstration of the applicability of the approach based on a case study and a software implementation concludes the work.
Bitcoin-NG is among the first blockchain protocols to approach the \emph{near-optimal} throughput by decoupling blockchain operation into two planes: leader election and transaction serialization. Its decoupling idea has inspired a new generation of high-performance blockchain protocols. However, the existing incentive analysis of Bitcoin-NG has several limitations. First, the impact of network capacity is ignored. Second, an integrated incentive analysis that jointly considers both key blocks and microblocks is still missing. In this paper, we aim to address these two limitations. First, we propose a new incentive analysis that takes the network capacity into account, showing that Bitcoin-NG can still maintain incentive compatibility against the microblock mining attack even under limited network capacity. Second, we leverage a Markov decision process (MDP) to jointly analyze the incentive of both key blocks and microblocks, showing that the selfish mining revenue of Bitcoin-NG is a little higher than that in Bitcoin only when the selfish miner controls more than 35\% of the mining power. We hope that our in-depth incentive analysis for Bitcoin-NG can shed some light on the mechanism design and incentive analysis of next-generation blockchain protocols.
We improve the fundamental security threshold of eventual consensus\nProof-of-Stake (PoS) blockchain protocols under the longest-chain rule by\nshowing, for the first time, the positive effect of rounds with concurrent\nhonest leaders.\n Current security analyses reduce consistency to the dynamics of an abstract,\nround-based block creation process that is determined by three events\nassociated with a round: (i) event $A$: at least one adversarial leader, (ii)\nevent $S$: a single honest leader, and (iii) event $M$: multiple, but honest,\nleaders. We present an asymptotically optimal consistency analysis assuming\nthat an honest round is more likely than an adversarial round (i.e., $\\Pr[S] +\n\\Pr[M] > \\Pr[A]$); this threshold is optimal. This is a first in the literature\nand can be applied to both the simple synchronous communication as well as\ncommunication with bounded delays.\n In all existing consistency analyses, event $M$ is either penalized or\ntreated neutrally. Specifically, the consistency analyses in Ouroboros Praos\n(Eurocrypt 2018) and Genesis (CCS 2018) assume that $\\Pr[S] - \\Pr[M] > \\Pr[A]$;\nthe analyses in Sleepy Consensus (Asiacrypt 2017) and Snow White (Fin. Crypto\n2019) assume that $\\Pr[S] > \\Pr[A]$. Moreover, all existing analyses completely\nbreak down when $\\Pr[S] < \\Pr[A]$. These thresholds determine the critical\ntrade-off between the honest majority, network delays, and consistency error.\n Our new results can be directly applied to improve the security guarantees of\nthe existing protocols. We also provide an efficient algorithm to explicitly\ncalculate these error probabilities in the synchronous setting. Furthermore, we\ncomplement these results by analyzing the setting where $S$ is rare, even\nallowing $\\Pr[S] = 0$, under the added assumption that honest players adopt a\nconsistent chain selection rule.\n
The demand for electricity increases rapidly along with the advancement of the industrial age. To ensure efficient distribution of the electricity, maintain low losses and high level of quality, and the security of electricity supply, the smart grid concept was proposed. The concept enables a small, individual scale to generate electricity and sell it to the grid. However, the concept adds complexity to the existing system, such as how a transaction between these generators and consumers are conducted, verified and recorded. This paper proposes the blockchain as a tool to manage transactions in the smart grid. Transactions are performed with smart contracts, and the network acts as a transaction verifier. The blockchain provides immutability of the transactions, which ensure every transaction between generators and consumers will always be executed. It also provides immutability to transaction history, which can be used for audit or solving a transaction dispute.
Mustafa Safa Özdayi, Murat Kantarcıoğlu, Bradley Malin
BACKGROUND: Blockchain has emerged as a decentralized and distributed framework that enables tamper-resilience and, thus, practical immutability for stored data. This immutability property is important in scenarios where auditability is desired, such as in maintaining access logs for sensitive healthcare and biomedical data. However, the underlying data structure of blockchain, by default, does not provide capabilities to efficiently query the stored data. In this investigation, we show that it is possible to efficiently run complex audit queries over the access log data stored on blockchains by using additional key-value stores. This paper specifically reports on the approach we designed for the blockchain track of iDASH Privacy & Security Workshop 2018 competition. In this track, participants were asked to devise an efficient way to run conjunctive equality and range queries on a genomic dataset access log trail after storing it in a permissioned blockchain network consisting of 4 identical nodes, each representing a different site, created with the Multichain platform. METHODS: Multichain duplicates and indexes blockchain data locally at each node in a key-value store to support retrieval requests at a later point in time. To efficiently leverage the key-value storage mechanism, we applied various techniques and optimizations, such as bucketization, simple data duplication and batch loading by accounting for the required query types of the competition and the interface provided by Multichain. Particularly, we implemented our solution and compared its loading and query-response performance with SQLite, a commonly used relational database, using the data provided by the iDASH 2018 organizers. RESULTS: Depending on the query type and the data size, the run time difference between blockchain based query-response and SQLite based query-response ranged from 0.2 seconds to 6 seconds. A deeper inspection revealed that range queries were the bottleneck of our solution which, nevertheless, scales up linearly. CONCLUSIONS: This investigation demonstrates that blockchain-based systems can provide reasonable query-response times to complex queries even if they only use simple key-value stores to manage their data. Consequently, we show that blockchains may be useful for maintaining data with auditability and immutability requirements across multiple sites.
Siyi Yang, Ahmed Hareedy, Robert Calderbank, Lara Dolecek
From currency to cloud storage systems, the continuous rise of the blockchain technology is moving various information systems towards decentralization. Blockchain-based decentralized storage networks (DSNs) offer significantly higher privacy and lower costs to customers compared with centralized cloud storage associated with specific vendors. Coding is required in order to retrieve data stored on failing components. While coding solutions for centralized storage have been intensely studied, topology-aware coding for heterogeneous DSNs have not yet been discussed. In this paper, we propose a joint coding scheme where each node receives extra protection through the cooperation with nodes in its neighborhood in a heterogeneous DSN with any given topology. As an extension of, which also subsumes, our prior work on coding for centralized cloud storage, our proposed construction preserves desirable properties such as scalability and flexibility in networks with varying topologies.
People have used cloud computing approach to store their data remotely. As auspicious as this approach is, it brings forth many challenges: from data security to time latency issues with data computation as well as delivery to end users. Fog computing has emerged as an extension for cloud computing to bring data processing and storage close to end-users; however, it minimizes the time latency issue but still suffers from data security challenges. For instance, when a fog node providing services to end users is compromised, the users' data security can be violated. Thus, this paper proposes a secure and fine-grained data access control scheme by integrating the CP-ABE algorithm and blockchain concept to prevent fog nodes from violating end users' data security in a situation where a compromised fog node is being ousted. We also classify the fog nodes into fog federations, based on their attributes such as services and locations, to minimize the time latency and communication overhead between fog nodes and cloud server. Further, the exploitation and integration of the blockchain concept and the CP-ABE algorithm enables fog nodes in the same fog federation to perform the authorization process in a distributed manner. In addition, to solve time latency and communication overhead problems, we equip every fog node with an off-chain database to store most frequently accessed data files for specific time, and with an on-chain access control policies table (On-chain Files Tracking Table) which must be protected from being tampered by malicious (rogue) fog nodes. Therefore, blockchain plays a vital role here as it is tamper-proof by nature. We demonstrate our scheme's efficiency and feasibility by designing algorithms and conducting a security analysis. The provided analysis shows that the proposed scheme is efficient and feasible in ousting malicious (rogue) fog nodes.
Keren Kezia Rejoice Adlin Mamangkey, Hendrik Manossoh, Heince R. N. Wokas
This study aims to determine how the development of regional financial capability in the North Sulawesi provincial government from its level of independence, level of dependency, decentralization ratio, and financial growth. The main characteristic of the region's ability to organize its government is the ability in its finances to finance the administration of the regional government. This type of research is qualitative research. Descriptive method is an analytical method used in this thesis research, that is every data - data obtained, analyzed based on theories relevant to the problem to be discussed to obtain the results of the analysis which is then concluded and provides advice. The results of descriptive analysis of the North Cellebes Province LRA APBD data show that from 2014 to 2018, the Regional Original Revenue development is still lacking, has not experienced a significant increase because Transfer Funds still dominate the Regional Revenue of North Cellebes Province. The conclusion is that there has been an improvement even though it is lacking, but based on the calculation of the financial ratios the Financial Ability is still in the near-able valuation.
The IRS recently issued its second description of how it will treat Bitcoin and other blockchain assets. Some of its analysis leaves open questions that invite further consideration, and important issues remain unresolved. Moreover, because the popular Bitcoin blockchain uses a "proof of work" consensus procedure, issues relating to the alternative "proof of stake" procedure have been neglected.
To promote coordinated development of electric vehicles (EVs) and power grid under open power selling, a bidding mechanism using blockchain smart contract technology was proposed. By demand respone management (DRM) on and off the blockchain, based on different driving characteristics of EV subgroups, various charging–discharging demands and constraints were fully considered between EV user subgroups and agent. Purchase–sale transaction relationship and unit commitment plan were fully considered between the EV agent and power dispatching center under economic dispatching. Aiming at the lowest power purchase cost of EV users, the highest profit of EV agent and the lowest cost of power economic dispatching, smart contract models with optimal benefits were established among the three. The smart contract models were solved by combining the internal and external optimization relationship of particle swarm and genetic algorithms. The charging–discharging price was optimized by DRM to realize the reasonable allocation of charging–discharging resources of EVs. An example analysis shows that this bidding mechanism can achieve peak–cutting and valley–filling for power load. At the same time, it can effectively protect the benefits of EV users, agent, and power dispatching center. This result can provide a reference for the application of smart contract in bidding of EVs to the power grid.