Decentralized currencies and similar blockchain applications require consensus. Bitcoin achieves eventual consensus in a fully-decentralized setting, but provides very low throughput and high latency with excessive energy consumption. In this paper, we propose identity aging as a novel and more efficient consensus approach. Our main idea is to establish reliable, long-term identities and choose the oldest identity as the miner on each round. Based on this approach, we design two blockchain systems. Our first system, SCIFER, leverages Intel's SGX attestation for identity bootstrapping in a partially-decentralized setting, where blockchain is permissionless, but we trust Intel for attestation. Our second system, DIFER, creates new identities through a novel mining mechanism and provides consensus in a fully-decentralized setting, similar to Bitcoin. One of the main benefits of identity aging is that it does not require constant computation. Our analysis and experiments show that identity aging provides significant performance improvements over Bitcoin with strong security guarantees.
Blockchain technology enables the creation of a decentralized environment, where transactions and data are not under the control of any third party organization. Any transaction ever completed is recorded in a public ledger in a verifiable, secure, transparent and permanent way, with a timestamp and other details. Introduced in 2009 as the core mechanism for the Bitcoin cryptocurrency and its worldwide payment system, blockchain has had many applications in domains such as IoT, finance, business, management, health and education. Also new platforms and tools for blockchain implementation were developed. As education becomes more open, diversified, democratised, and decentralised, the blockchain technology is taken in consideration by researchers, teachers and institutions, to maintain reputation, trust in certification, and proof of learning. In the first part of the paper, we explore the blockchain technology. Next, existing global and governmental initiatives, together with potential applications of blockchain in different domains are presented. The need to learn about this emerging technology is demonstrated, together with pioneering cases in different universities. Then we propose a public blockchain called OpenEduChain, designed as a repository for open educational assets (Open Educational Resources - OERs, Massive Open Online Courses - MOOCs, open pedagogies and scenarios), but also to deliver issued certificates and open badges by universities and other educational and training institutions. At university level, OpenEduChain, implemented on Ethereum, is used to store data about the open educational items created by faculty members and students. Also digital certificates or open badges are provided to the participants in the trainings and workshops. After a period of tests, OpenEduChain usage could be extended at national level, but also for new purposes such as e-portfolios or assessment.
Bettina Nissen, Larissa Pschetz, Dave Murray-Rust, Hadi Mehrpouya · 6 authors
Design and HCI researchers are increasingly working with complex digital infrastructures, such as cryptocurrencies, distributed ledgers and smart contracts. These technologies will have a profound impact on digital systems and their audiences. However, given their emergent nature and technical complexity, involving non-specialists in the design of applications that employ these technologies is challenging. In this paper, we discuss these challenges and present GeoCoin, a location-based platform for embodied learning and speculative ideating with smart contracts. In collaborative workshops with GeoCoin, participants engaged with location-based smart contracts, using the platform to explore digital 'debit' and 'credit' zones in the city. These exercises led to the design of diverse distributed-ledger applications, for time-limited financial unions, participatory budgeting, and humanitarian aid. These results contribute to the HCI community by demonstrating how an experiential prototype can support understanding of the complexities behind new digital infrastructures and facilitate participant engagement in ideation and design processes.
Proof-of-Stake systems randomly choose, on each round, one of the\nparticipants as a consensus leader that extends the chain with the next block\nsuch that the selection probability is proportional to the owned stake.\nHowever, distributed random number generation is notoriously difficult. Systems\nthat derive randomness from the previous blocks are completely insecure;\nsolutions that provide secure random selection are inefficient due to their\nhigh communication complexity; and approaches that balance security and\nperformance exhibit selection bias. When block creation is rewarded with new\nstake, even a minor bias can have a severe cumulative effect.\n In this paper, we propose Robust Round Robin, a new consensus scheme that\naddresses this selection problem. We create reliable long-term identities by\nbootstrapping from an existing infrastructure, such as Intel's SGX processors,\nor by mining them starting from an initial fair distribution. For leader\nselection we use a deterministic approach. On each round, we select a set of\nthe previously created identities as consensus leader candidates in round robin\nmanner. Because simple round-robin alone is vulnerable to attacks and offers\npoor liveness, we complement such deterministic selection policy with a\nlightweight endorsement mechanism that is an interactive protocol between the\nleader candidates and a small subset of other system participants. Our solution\nhas low good efficiency as it requires no expensive distributed randomness\ngeneration and it provides block creation fairness which is crucial in\ndeployments that reward it with new stake.\n
Elli Androulaki, Artem Barger, Vita Bortnikov, Christian Cachin · 21 authors
The success of public blockchains, such as Bitcoin and Ethereum, led to growing interest in Blockchain technology and its application as a distributed system in the most innovative business use cases.
M. Harris Haseeb, K. Raja Sekhar, Y V. Spandana, M Syam
Block chain is a trust which can be best understood by the state machine replication, It is decentralized distributed ledger which is along all peers in the network connected through nodes over Internet. Every Node in the chain have equal stake and also the main factor is every node which have greater CPU cycles has a chance to operate node by spending those CPU cycles and also show Proof Of Work. Hence when the block chain is used in Business Models it loses its Private transactions and Confidential Contracts.
Given the parallels between game theory and consensus, it makes sense to intelligently design blockchain or DAG protocols with an incentive-compatible-first mentality. To that end, we propose a new blockchain or DAG protocol enhancement based on delayed rewards. We devise a new method for imposing slashing conditions on miner behavior, using their delayed rewards as stake in a Proof of Work system. Using fraud proofs, we can slash malicious miner behavior and reward long-lived, honest behavior.
A trusted electronic election system requires that all the involved information must go public, that is, it focuses not only on transparency but also privacy issues. In other words, each ballot should be counted anonymously, correctly, and efficiently. In this work, a lightweight E-voting system is proposed for voters to minimize their trust in the authority or government. We ensure the transparency of election by putting all message on the Ethereum blockchain, in the meantime, the privacy of individual voter is protected via an efficient and effective ring signature mechanism. Besides, the attractive self-tallying feature is also built in our system, which guarantees that everyone who can access the blockchain network is able to tally the result on his own, no third party is required after voting phase. More importantly, we ensure the correctness of voting results and keep the Ethereum gas cost of individual participant as low as possible, at the same time. Clearly, the pre-described characteristics make our system more suitable for large-scale election.
Cryptocurrencies have experienced recent surges in interest and price. It has been discovered that there are time intervals where cryptocurrency prices and certain online and social media factors appear related. In addition it has been noted that cryptocurrencies are prone to experience intervals of bubble-like price growth. The hypothesis investigated here is that relationships between online factors and price are dependent on market regime. In this paper, wavelet coherence is used to study co-movement between a cryptocurrency price and its related factors, for a number of examples. This is used alongside a well-known test for financial asset bubbles to explore whether relationships change dependent on regime. The primary finding of this work is that medium-term positive correlations between online factors and price strengthen significantly during bubble-like regimes of the price series; this explains why these relationships have previously been seen to appear and disappear over time. A secondary finding is that short-term relationships between the chosen factors and price appear to be caused by particular market events (such as hacks / security breaches), and are not consistent from one time interval to another in the effect of the factor upon the price. In addition, for the first time, wavelet coherence is used to explore the relationships between different cryptocurrencies.
We present a detailed bubble analysis of the Bitcoin to US Dollar price dynamics from January 2012 to February 2018. We introduce a robust automatic peak detection method that classifies price time series into periods of uninterrupted market growth (drawups) and regimes of uninterrupted market decrease (drawdowns). In combination with the Lagrange Regularisation Method for detecting the beginning of a new market regime, we identify 3 major peaks and 10 additional smaller peaks, that have punctuated the dynamics of Bitcoin price during the analyzed time period. We explain this classification of long and short bubbles by a number of quantitative metrics and graphs to understand the main socio-economic drivers behind the ascent of Bitcoin over this period. Then, a detailed analysis of the growing risks associated with the three long bubbles using the Log-Periodic Power Law Singularity (LPPLS) model is based on the LPPLS Confidence Indicators, defined as the fraction of qualified fits of the LPPLS model over multiple time windows. Furthermore, for various fictitious 'present' times $t_2$ before the crashes, we employ a clustering method to group the predicted critical times $t_c$ of the LPPLS fits over different time scales, where $t_c$ is the most probable time for the ending of the bubble. Each cluster is proposed as a plausible scenario for the subsequent Bitcoin price evolution. We present these predictions for the three long bubbles and the four short bubbles that our time scale of analysis was able to resolve. Overall, our predictive scheme provides useful information to warn of an imminent crash risk.
Jakob Demant, Rasmus Munksgaard, David Décary-Hêtu, Judith Aldridge
Objective: There is broad agreement in the literature on the transformative potential of drug cryptomarkets that allow sourcing on a global market and consequently the circumvention of existing supply chains between producer and end user. We examine whether the transformative potential of drug cryptomarkets has been realized in two ways: Are cryptomarket drug sellers found in production and transit countries? and Do we see the increased use of shipping across international borders over time? Method: Using data collected by the DATACRYPTO software tool between 2013 and 2016, we characterize cryptomarket buyer behavior through the product reviews (i.e., sales transactions) posted on 15 cryptomarkets. Findings: Cryptomarket drug sellers are predominantly based in countries of Europe, North America, and Oceania. For both cannabis resin and cocaine sold on cryptomarkets, we find that known production and transit countries are not the primary sources of supplied drugs but rather key countries of consumption. In the case of 3,4-methylenedioxymethamphetamine, we observe that the Netherlands, a known production country, is the largest supplier. We further observe tendencies over time toward increased localization of cryptomarkets with regard to product destinations. Discussion: Though cryptomarkets offer a potentially global platform for drug distribution, they do not tend to be used as such. We explain our results with reference to buyers’ preferences regarding safety, risk, and convenience, alongside structural limitations for cryptomarket use such as bitcoin availability.
Summary Fog computing is a new computing paradigm that can provide flexible resources and services at the edge of network. It is an extension of cloud computing and usually cooperated with cloud computing. Therefore, end users, fog nodes, and cloud servers can form a three‐layer service model in practical application. In this model, they should have an agreement on a service contract, which contains every party's rights and obligations before the beginning of the service. However, due to lack of trust, it will suffer from some fairness problems during signing a service contract. Contract signing protocol allows two or more mutual distrust entities to sign a predefined digital contract in a fair and effective way. In this paper, we propose a fair three‐party contract signing protocol based on the primitive of blockchain, which can be applied to the scenario of fog computing. Our proposed construction allows the participants to sign a contract in a fair way without the involvement of an arbitrator. Moreover, the privacy of the contract content can be preserved on the public chain. Finally, we realize the proposed protocol through the private blockchain and provide the experimental simulation that analyzes the efficiency and effectiveness.
In this paper, by using econometric techniques we provide evidence that bitcoin exhibited the formation of speculative bubble in 2017. To conceptually rationalize the results, we delve into the extant theoretical approaches developed by Kindleberger's (1978) speculative bubbles and Minsky's (1992) financial instability hypothesis. Certainly, bitcoin has spurred a revolution in payment technology that, if treated cautiously can facilitate financial intermediation and inclusion. Ultimately, whether or not bitcoin constitutes a bubble is a decision for investors as the road to hell is paved with good promises.
We present two models of the block chain of Bitcoin in the interactive theorem prover Agda. The first one is based on a simple model of bank accounts, while having transactions with multiple inputs and outputs. The second model models transactions, which refer directly to unspent transaction outputs, rather than user accounts. The resulting blockchain gives rise to a transaction tree. That model is formalised using an extended form of induction-recursion, one of the unique features of Agda. The set of transaction trees and transactions is defined inductively, while simultaneously recursively defining the list of unspent transaction outputs. Both structures model standard transactions, coinbase transactions, transaction fees, the exact message to be signed by those spending money in a transaction, block rewards, blocks, and the blockchain, and the second structure models as well maturation time for coinbase transactions and Merkle trees. Hashing and cryptographic operations and their correctness are dealt with abstractly by postulating corresponding operations. An indication is given how the correctness of this model could be specified and proven in Agda.
We propose a conceptual design for a quantum blockchain. Our method involves encoding the blockchain into a temporal GHZ (Greenberger-Horne-Zeilinger) state of photons that do not simultaneously coexist. It is shown that the entanglement in time, as opposed to an entanglement in space, provides the crucial quantum advantage. All the subcomponents of this system have already been shown to be experimentally realized. Furthermore, our encoding procedure can be interpreted as nonclassically influencing the past.
Stanisław Drożdż, Robert Gȩbarowski, Ludovico Minati, Paweł Oświȩcimka · 5 authors
Based on 1-minute price changes recorded since year 2012, the fluctuation properties of the rapidly-emerging Bitcoin (BTC) market are assessed over chosen sub-periods, in terms of return distributions, volatility autocorrelation, Hurst exponents and multiscaling effects. The findings are compared to the stylized facts of mature world markets. While early trading was affected by system-specific irregularities, it is found that over the months preceding Apr 2018 all these statistical indicators approach the features hallmarking maturity. This can be taken as an indication that the Bitcoin market, and possibly other cryptocurrencies, carry concrete potential of imminently becoming a regular market, alternative to the foreign exchange (Forex). Since high-frequency price data are available since the beginning of trading, the Bitcoin offers a unique window into the statistical characteristics of a market maturation trajectory.
As an integral part of V2G networks, EVs receive electricity from not only the grid but also other EVs and may frequently feed the power back to the grid. Payment records in V2G networks are useful for extracting user behaviors and facilitating decision-making for optimized power supply, scheduling, pricing, and consumption. Sharing payment and user information, however, raises serious privacy concerns in addition to the existing challenge of secure and reliable transaction processing. In this article, we propose a blockchain-based privacy preserving payment mechanism for V2G networks, which enables data sharing while securing sensitive user information. The mechanism introduces a registration and data maintenance process that is based on a blockchain technique, which ensures the anonymity of user payment data while enabling payment auditing by privileged users. Our design is implemented based on Hyperledger to carefully evaluate its feasibility and effectiveness.
Farinaz Sabz Ali Pour, Unal Tatar, Adrian Gheorghe
Sand is a key ingredient for many industries, including concrete, glass, and electronics. Sand extraction is now exceeding fossil fuels and biomass. The absence of data on aggregates sand mining makes assessments difficult and has contributed to the lack of awareness about this issue. A sand governance business framework is developed applying the blockchain technology as the main goal of this study to regulate the sand extraction and trade. Blockchain technology provides a distributed concurrency monitoring system for the supply management. Agent-Based Modeling and Simulation (ABMS) as an effective bottom-up tool is applied to demonstrate the application of the model. The sand providers and users are modeled as a collection of autonomous decision-making entities called agents. The agents interact with each other, the regulators participate in making decisions on the basis of a set of rules that are defined within the blockchain network.
Yaygınlaşaninternet kullanımı geleneksel ticaret kavramında değişikliklere neden oluphayatımıza yeni uygulamalar ve yeni kavramlar kazandırmıştır. Bu uygulamalardanbiri de e- ticarettir. E- ticaretlebirlikte insanlar para yerine alternatif ödeme şekillerine yönelmişlerdir. Ekonomik ve bilimsel gelişime paralelolarak para soyutlaşmıştır. Özellikle son yıllarda dijital ve sanal paranınkullanımını dikkat çekici bir şekilde yaygınlaşmıştır ve Bitcoin bunun endikkat değer örneklerinden biridir. Bitcoin; açık kaynaklı bir kod olarak üretilmiş kriptolu bir dijital ve bağımsızpara birimidir. Bitcoin diğer para birimleri gibi, alışverişlerimizde veçevrimiçi ortamlarda harcayabileceğimiz bir para birimidir. Bitcoin, merkezibir otoriteye bağlı değildir. Çünkü Bitcoin, merkez bankalarının kontrolündedeğil, ağ üzerinde üretilmektedir. Yani yasal bir denetim söz konusu değildir. Bankaaracılığıyla yapılan para transferlerinde pek çok engel ortaya çıkabilir.Bitcoin sisteminde haftanın her günü ve her saatinde para transferleri hızlıbir şekilde gerçekleştirilir. Bitcoin hesapları, ücretsiz olup sorgusuz sualsizaçılabilme özelliğine sahiptir. Ayrıca sistem kullanıcı bilgileri hakkındabilgi vermez. Bu çalışmada paranın tanımı, özellikleri vefonksiyonları yeniden ele alınarak dijital paranın tarihsel gelişimi, sanal parakonsepti ve kripto para kavramları değerlendirilmiştir. Çalışmada her geçen gündaha popüler hale gelen Bitcoin’in tarihsel arka planı, olumlu ve olumsuzyönleri ve piyasası ele alınmıştır.
Turkish Abstract: Yayginlasan internet kullanimi geleneksel ticaret kavraminda degisikliklere neden olup hayatimiza yeniuygulamalar ve yeni kavramlar kazandirmistir. Bu uygulamalardan biri de e-ticarettir. E-ticaretle birlikte insanlarpara yerine alternatif odeme sekillerine yonelmislerdir. Ekonomik ve bilimsel gelisime paralel olarak para soyutlasmistir. Ozellikle son yillarda dijital ve sanal paranin kullanimini dikkat cekici bir sekilde yayginlasmistir ve Bitcoin bunun en dikkate deger orneklerinden biridir. Bitcoin; acik kaynakli bir kod olarak uretilmis kriptolu bir dijital ve bagimsiz para birimidir. Bitcoin diger para birimleri gibi, alisverislerimizde ve cevrimici ortamlarda
harcayabilecegimiz bir para birimidir. Bitcoin, merkezi bir otoriteye bagli degildir. Cunku Bitcoin merkez bankalarinin kontrolunde degil, ag uzerinde uretilmektedir. Yani yasal bir denetim soz konusu degildir. Banka araciligiyla yapilan para transferlerinde pek cok engel ortaya cikabilir. Bitcoin sisteminde haftanin her gunu ve her saatinde para transferleri hizli bir sekilde gerceklestirilir. Bitcoin hesaplari, ucretsiz olup sorgusuz sualsiz acilabilme ozelligine sahiptir. Ayrica sistem kullanici bilgileri hakkinda bilgi vermez. Bu calismada paranin tanimi, ozellikleri ve fonksiyonlari yeniden ele alinarak dijital paranin tarihsel gelisimi, sanal para konsepti ve
kripto para kavramlari degerlendirilmistir. Calismada her gecen gun daha populer hale gelen Bitcoin’in tarihsel arka plani, olumlu ve olumsuz yonleri ve piyasasi ele alinmistir.
English Abstract: The increasing use of the internet has caused changes in the concept of traditional trade and introduced new applications and new concepts to our life. One of these applications is e-commerce. With e-commerce, people have bent to alternative forms of payment instead of money. Parallel to economic and scientific development, money has been abstracted. Especially in recent years, the use of digital and virtual money has become remarkably widespread and Bitcoin is one of the most well-marked example of this. Bitcoin; is a cryptographic digital and independent currency produced as an open source code. Like other currencies, Bitcoin is a currency that we can spend in our shopping and online environments. Bitcoin is not connected to a central authority. Because Bitcoin is not under the control of the central banks, it is produced on the network. And so there is no legal control. Many obstacles may occur in the transfer of funds through the bank. On the other hand in the Bitcoin system, money transfers are carried out quickly every day and every hour of the week. Bitcoin accounts are free and opened unquestioned. In addition, the system does not provide information about user. In this study, the definition, characteristics and functions of money are reviewed and the historical development of digital money, virtual money concepts and crypto money concepts are evaluated. The historical background, positive and negative aspects and market of Bitcoin, which became more popular every day has been discussed in the study.