Ring signatures are cryptographic protocols designed to allow any member of a group to produce a signature on behalf of the group, without revealing the individual signer's identity. This offers group members a level of anonymity not attainable through generic digital signature schemes. We call this property 'plausible deniability', or anonymity with respect to an anonymity set. We concentrate in particular on implementing privacy on the blockchain, introducing a unique ring signature scheme that works with existing blockchain systems. We implement a unique ring signature (URS) scheme using secp256k1, creating the first implementation compatible with blockchain libraries in this way, so as for easy implementation as an Ethereum smart contract. We review the privacy and security properties offered by the scheme we have constructed, and compare its efficiency with other commonly suggested approaches to privacy on the blockchain.
The increasing collective use of distributed application software platforms, programming languages and crypto-currencies around the blockchain concept for general transactions may have radical implications for the way in which society conceptualises and applies trust and trust-based social systems such as law. By exploring one iteration of such generalised blockchain systems – Ethereum – and the historical lineage of such systems, it will be argued that indeed their ideological basis is largely one of distrust, decentralisation and, ultimately, via increasing disassociation of identity, a fear of the body itself. This ideological basis can be reframed as a crypto-legal approach to the problems of human interaction, one whereby the purely technological solutions outlined above are considered adequate for reconciling many of the problems of our collective existence. The article concludes, however, by re-iterating a perspective of law more so as an entirely embodied and trust dependent notion. These aspects go some way to explaining the necessarily centralised role it takes on within societies. They also explain why the crypto-legal approaches advanced by systems like Ethereum – or even the co-opting of blockchain technology by law firms themselves – will only ever be at best efficiency exercises concerned with the processing of data relating to legal affairs, and not the more radical, ambiguous and difficult process of actual legal thought or, indeed, engagement with trust.
The sharing economy, the business of collectively using pri- vately owned objects and services, has fuelled some of the fastest growing businesses of the past years. However, popular sharing platforms like Airbnb or Uber exhibit several draw- backs: a cumbersome sign up procedure, lack of participant privacy, overbearing terms and conditions, and significant fees for users. We demonstrate a Decentralised App (DAPP) for the sharing of everyday objects based on a smart contract on the Ethereum blockchain. This contract enables users to register and rent devices without involvement of a Trusted Third Party (TTP), disclosure of any personal information or prior sign up to the service. With increasing distribution of cryptocurrencies the use of smart contracts such as proposed in this paper has the potential to revolutionise the sharing economy.
The sharing economy, the business of collectively using privately owned objects and services, has fuelled some of the fastest growing businesses of the past years. However, popular sharing platforms like Airbnb or Uber exhibit several drawbacks: a cumbersome sign up procedure, lack of participant privacy, overbearing terms and conditions, and significant fees for users. We demonstrate a Decentralised App (DAPP) for the sharing of everyday objects based on a smart contract on the Ethereum blockchain. This contract enables users to register and rent devices without involvement of a Trusted Third Party (TTP), disclosure of any personal information or prior sign up to the service. With increasing distribution of cryptocurrencies the use of smart contracts such as proposed in this paper has the potential to revolutionise the sharing economy.
During this decade we have witnessed the introduction or scaling of several forms of alternative currencies. The Alternative Currency Database includes more than 300 local alternative paper currencies. Cryptocurrencies such as Bitcoin represent non-government backed digital currencies that have grown substantially through the underlying blockchain technology. Timebanking is another form of alternative currency where more than four million hours of time have been exchanged for future time from network members around the globe. I believe we are on the cusp of a transformation in how value is captured and exchanged in society. Much of this change is driven by a grassroots, and technologically-empowered movement, to confront the ills perceived to be powered and exacerbated by market-based capitalism, such as climate change and income inequality. I will argue that alternative currencies discourage passive investment, and therefore serve as a powerful alternative to market-based capitalism. Throughout this essay, I refer to ‘traditional currencies’ as strong currencies and alternative currencies as ‘weak currencies’. Strong currencies allow for, and frequently incorporate incentives for investors, speculators, financiers and others to hoard or leverage money for economic gain, whereas weak currencies are those with no inherent incentive in accumulating the currency, and in fact, may have built-in disincentives to do so. Before describing each of the three forms of alternative currencies of interest in this essay (local paper currency, timebanking and cryptocurrency) it is worth briefly reviewing current thinking about alternative currencies. While management scholars have largely been blinded by the emergence of alternative currencies, scholars in many other fields have explored alternative currencies from multiple perspectives. Currencies are a mechanism for enabling an exchange between parties. Whereas traditional currencies are backed by nation states, alternative currencies are not. Political scientists have been exploring local currencies as a challenge to the legitimacy of nation states for decades (e.g., Williams, 1996). The resistance to the power of the state, expressed as growth in alternative, non-government backed currencies, contributes to the positioning of alternative currencies as a response to perceived failures of capitalism and the nation states that continue to support market-based capitalism. Similarly, economists have long viewed the birth of alternative currencies as a grassroots movement against capitalism, free-trade and globalization. In this sense, one could view alternative currencies as a manifestation of a social movement, a resistance against perceived ills brought by free trade, nation building and more recently, the increasing automation of work (often referred to as industry 4.0 or the fourth industrial revolution) which is leading to a sizable increase in freelancing and the ‘on-demand economy’. While much of the growth in freelancing is driven by capitalist tendencies of corporations to increase efficiencies and drive down costs there is also a growing interest in freelance and independent forms of work particularly amongst the millennial generation (Cohen, 2016). The growth in freelancing opens up avenues for the application of alternative currencies, particularly timebanking, whereby peers connected by platforms can exchange expertise without exchanging cash. So why do I view the weak nature of most alternative currencies to be a positive transformational condition for alternative currencies? As corporations continue to eliminate jobs due to efficiency gains and automation, many corporations and their shareholders are getting richer while much of the population is getting poorer. Alternative currencies being weak currencies mitigate wealth accumulation in the hands of a few and empower participants to benefit more directly from their contributions to the exchange system. The growing evidence suggests that market-based capitalism is adequate to good at supporting returns to passive investors. Venture capitalist and investors in publicly traded corporations have witnessed gains in recent decades, meanwhile employees of those companies, and society at large have failed to experience the same benefits. While the United Stated is in an economic recovery from the great recession, underemployment and income inequality continue to grow. The short-term profit maximization encouraged by investors in the stock market, and the quick path to exits for start-ups targeted by venture capitalists have yielded wealth accumulation in the hands of a few, yet resulted in little benefit to society as a whole. Proponents of a post-capitalist movement leverage the evidence of growing income inequalities and the shift of capital and wealth to the financial markets to suggest that we are witnessing the decline of capitalism due to what historian Ferdinand Braudel (1992) referred to as the financial autumn theory. When citizens, makers and producers of value in society share less in the economic benefits of their activity, while the financial players reap growing percentages of such economic activity, Braudel suggests this to be a signal that the prevailing economic model has reached its maturity. Alternative currencies yield business models that penalize hoarding and returns on investment, and instead focus on velocity of community-based transactions amongst peers and local businesses. Passive investors in the alternative currencies arena, therefore have little to gain. Where alternative currencies are weak and the orientation is on high velocity transactions, the active participants of the transactions will benefit more than passive investors. This is what positions alternative currencies as a direct reaction of the masses to the ‘financialization’ of the markets. Financialization occurs when lenders, financiers and investment bankers increasingly profit from citizens and consumers, through student loans, car loans, mortgages, credit cards and several other financial instruments. Forbes (Collins, 2015) defined financialization as ‘the growing scale and profitability of the finance sector at the expense of the rest of the economy and the shrinking regulation of its rules and returns’, highlighting that between 1970 and 2010, the finance industry doubled its share of GDP from 10 per cent to 20 per cent. Alternative currencies being weak currencies pose the potential to serve as tools for facilitating more direct exchange of value between peers and local businesses, at the same time, give little opportunity for the financialization we have witnessed in recent decades in market-based economies. Furthermore, the role of weak alternative currencies in transforming the relationship between founders, users, employees and investors amongst start-ups is a fascinating one. I would even argue that if we see a meaningful shift towards post-capitalist models, we will see the death of venture capital as we currently view it. As it is, we have collectively overhyped the importance of venture capital given its very small contribution to the global economy and the miniscule percentage of start-ups that receive venture capital. For example, a recent study by the Kaufman Foundation found that less than five percent of start-up funding in the United States comes from venture capital sources and only 6.5 per cent of high growth start-ups had received venture capital. I will briefly explore this concept in the context of each of the three alternative currencies that are the subject of this essay. In some form or another local currencies have been around for centuries, and of course pre-date modern, treasury-backed currencies at the national level. But since the widespread adoption of national currencies, local alternative currencies have had a place in societies around the globe. They have been commonly implemented in a grassroots fashion as a response to economic shocks, such as in Argentina after the economic crisis around the start of the twenty-first century. More recently, Spain for example, witnessed the introduction of a dozen local currencies following the 2008 crisis and, similarly, as the Wall Street Journal reported in 2015, Greece has experienced a big boost in the alternative currency movement. Perhaps surprisingly, local paper currencies are also flourishing in more than 50 communities throughout the United States. BerkShares, founded in 2006 in Berkshire, Massachusetts, are actually acquired by exchanging U.S. dollars for this local currency, which then must remain in the community. More than 400 local businesses in the community accept BerkShares for payment. The goal of BerkShares is to ‘maximize the circulation of goods, services, and capital within the region… and to distinguish the local businesses that accept the currency from those that do not’.1 While each local currency operates differently, these initiatives all seek to support local communities over foreign companies and investors. Local physical currencies are the epitome of weak currencies as they are virtually impossible to accumulate at any large scale that would give any single holder monopolistic rights. In fact it would be useless to achieve such a position because local currencies are only valuable with a local, active exchange system. Therefore, I have uncovered no examples of private passive investors in local paper currencies, suggesting that this form of currency does not enable the same dispersion between corporate and investor gains without social gains. To further reduce such a risk, many local currency systems implement a negative interest rate mechanism that serves to significantly disincent their hoarding. The concept behind timebanking is that instead of delivering a service in return for monetary reward, a member of a timebanking community can offer service to another member and then receive time credit to be utilized within the same timebanking community, but by any other member. The recipient of the original service is not obligated to deliver a service in return to the same member, but, instead, becomes indebted to the community and will owe an equivalent amount of time to another member. It is virtually impossible to accumulate time credit to a point where any individual in the community can exert monopoly power over the community. Thus timebanking is clearly a weak currency. Historically timebanking has been a very localized phenomenon relying on locally provided services to other members living in close proximity. Yet new social networking and video technologies allows for timebanking to potentially scale regionally or even globally. Brazil-based Bliive, for example, has facilitated the sharing of more than 100,000 hours of expertise in return for time credit through an online platform which connects primarily local timebankers to exchange value and expertise. Although in the case of Bliiive, their technology still primarily facilitates local interactions. My wife, currently enrolled in an Executive MBA program at EADA Business school is leading the development of a platform called the Professional Knowledge Exchange (PKX). This is one of the first timebanking initiatives I have discovered which hopes to leverage technology to connect global professionals. Instead of manual labour or local professional services, PKX aims to connect engineers, doctors, executives and other professionals in a global peer-to-peer network. A paediatrician based in Venezuela could seek expertise from a paediatrician in Brazil regarding most effective treatments of the Zika virus. Or an entrepreneur in Santiago, Chile seeking to launch an electric vehicle car sharing service could use PKX to find an expert from Paris who helped implement their Autolib'service. PKX plans to offer a hybrid model whereby users can choose to timebank or pay per hour of expertise sought. The first known experiments with cryptocurrencies occurred in the Netherlands in the mid-1980s. Yet, cryptocurrencies took off as something of note with the introduction of Bitcoin in 2008. The brainchild of a mysterious and as of yet unidentified person or group of persons, with the pseudonym, Satashio Nakamoto, Bitcoin emerged as a global, digital currency not controlled or supported by any government, i.e. a borderless, digital, alternative currency. Bitcoin is intended to be an anonymous digital currency that allows for transactions between individual without intermediaries. If I own bitcoins and want to buy your computer with bitcoins, we can agree on the value of the computer and I can transfer the Bitcoin equivalent value to you immediately. Thanks to the underlying blockchain technology I will discuss shortly, this transaction is instantaneous and recorded for eternity within the Bitcoin network. Bitcoin is not as weak of a currency as the others described in this essay as it is possible for an individual or group of individuals to accumulate bitcoins or even engage in currency speculation. The Bitcoin protocol has established that there will never be more than 21 million total bitcoins in circulation. The fact that there is a maximum limit could eventually incent investors and speculators to hoard bitcoins in the hopes that hoarding bitcoins could lead to a shortage and drive up their value. As such Bitcoin may appear to be out of context in an essay about alternative currencies as a post capitalist response. In fact, Bitcoin has had some big successes in the start-up community with more than $1 billion (USD) venture capital invested in Bitcoin start-ups since 2012 and $690 million in 2015 alone2. Bitcoin has also gained some traction in terms of owners of bitcoin currency being able to engage in online and physical transactions around the globe. Recently some companies have begun to introduce Bitcoin ATMs as well. Yet, Bitcoin did emerge as part of the 99 per cent movement and the frustration with banks too big to fail and failures of federal governments to implement policies which yield prosperity for all income classes. It is possible that Bitcoin may end up being just another form of market-based capitalism. What is perhaps more intriguing about Bitcoin and its role in facilitating a shift towards post capitalism, is its underlying technology known as blockchain. Blockchain is a distributed ledger technology that simultaneously records every Bitcoin transaction with every node or computer on the system around the globe. Industry experts, such as Goldman Sachs suggest that blockchain tech could eventually be worth tens of billions of dollars in finance, insurance and related industries. Of course this insight from Goldman Sachs does not inspire interest in post-capitalism as it may just help increase the profits of those already engaged in financialization while also contribute to more automation and job losses. However, beyond its impact on mainstream industries operating with market-based capitalistic models, blockchain, and similar derivatives like ethereum, pose significant opportunities for radically new forms of post-capitalist organizing, which I will discuss at the end of this essay. Throughout this essay I have suggested that the post-capitalist movement seeks to leverage technology to facilitate connecting peers (and local businesses) in the hopes of more equitable distribution of income for makers and creators. The sharing economy broadly seeks to facilitate such peer-to-peer transactions (P2P) usually with an intermediary who owns the underlying technology. It may be enlightening to explore one of the highest profile examples of market spaces in this emerging distributed arena and the vast implications for management that emerge. Uber, a global powerhouse of the technologically-enabled taxi service, raised a recent funding round based on a valuation of $62.5 billion making Uber more valuable than General Motors and any other tech company based in Silicon Valley. Yet, Uber has had well publicized problems with regulators around the globe in part due to incumbent resistance (i.e., mainstream taxi fleets), concerns regarding Uber's bypassing taxi regulations for safety of drivers and passengers, and of course concerns about the low income and lack of benefits afforded to drivers. Uber's success to some extent can be attributed to the lack of innovation from taxi operators around the globe. Uber met a latent need for a location-based, highly technologically-enabled transportation service. Initiatives to create what some refer to as a platform coop, such as those of 645 taxi drivers in Denver, Colorado who came together to offer the same innovative service as Uber but without a global platform owner dictating the terms, certainly challenge the dominance of intermediaries like Uber, resulting in more equitable value capture. Yet platform cooperatives are really just an alternative form of governance operating within and competing amongst capitalist enterprises. However, there is another potential response to Uber, driven by blockchain technology which could truly be disruptive and provides insights as to where this space could go. What if technology could facilitate transactions between two parties without the need for an intermediary that may be inclined to take extractive approaches such as those by Uber and Airbnb? Could you design a system with open source software that is developed by the community which facilitates direct transactions between peers without anyone taking a cut? Instead of cooperatives where members share in the ownership of the enterprise, a DAO actually has no owners and no profit share. In theory, 100 per cent of the income from transactions in a DAO can flow to the provider of services with no intermediary taking their cut. The transactions in a DAO could take the form of local currency, digital currency, national currency or a combination. While there is no taxi DAO formed yet, there is certainly talk of them as an alternative, post-capitalist solution to Uber. Other DAOs have been formed recently, such as openbazaar, which seeks to essentially offer the same type of service as eBay, i.e., an online classified ads without a or So you could offer to that computer I but this time and we could agree on a and I would pay you directly for it without anyone like taking a percentage of the In this DAOs are post-capitalist platforms for to exchange without intermediaries. As can be from the taxi there are several emerging in the towards post-capitalism and alternative currencies that be intriguing to management of these how do industry to from post-capitalist models like DAOs if a DAO emerged to Uber, how would it emerging business models which are between market-based and post-capitalist and DAOs as an form that is to private ownership But when a business model is weak currencies, the incentive to accumulate wealth through the maximum of value of transactions This suggests any returns would The DAO a potential the as does the growing insights from the use of The post-capitalism movement to many regarding the shift towards local cooperatives and further challenge of the importance of nation As in the to it that on many social and is at the local and not the such as the United or even the Therefore, and alternative currencies expressed as a manifestation of the 99 per cent movement, suggest a need for or new for why do what they do and with what In a post-capitalist may be by the have no profit in alternative currencies, and only to enable to transactions whereby all value from the transaction will be by the the value. I find it for that the focus of on the that the valuation of tech start-ups when they an and I exploring how the drive for exits of start-ups and short-term profits of publicly traded companies has to and is the emergence of a new economic alternative currencies, in response to the perceived ills by and investors in publicly traded Yet, I it increasingly to the growing being driven by the we find in market-based capitalism while also some for a future where those who actually create value in a peer-to-peer economy share more in the of their contributions with the help of platforms and a growing of alternative currencies. In of Paris it had already a to launch its own alternative, local currency. If the currency, the is Paris would be the and the first capital to launch and support the of an alternative local currency and perhaps be that this movement may just be getting If money is between the and the as perhaps the growing use of alternative currencies is an of to This essay on with most and several with and If this essay has any on or in the it will be largely due to the the had on its and
Thanks to their anonymity (pseudonymity) and elimination of trusted intermediaries, cryptocurrencies such as Bitcoin have created or stimulated growth in many businesses and communities. Unfortunately, some of these are criminal, e.g., money laundering, illicit marketplaces, and ransomware. Next-generation cryptocurrencies such as Ethereum will include rich scripting languages in support of smart contracts, programs that autonomously intermediate transactions. In this paper, we explore the risk of smart contracts fueling new criminal ecosystems. Specifically, we show how what we call criminal smart contracts (CSCs) can facilitate leakage of confidential information, theft of cryptographic keys, and various real-world crimes (murder, arson, terrorism).
Roman Matzutt, Oliver Hohlfeld, Martin Henze, Robin Rawiel · 6 authors
As transaction fees skyrocket today, blockchains become increasingly expensive, hurting their adoption in broader applications. This work tackles the saving of transaction fees for economic blockchain applications. The key insight is that other than the existing "default'' mode to execute application logic fully on-chain, i.e., in smart contracts, and in fine granularity, i.e., user request per transaction, there are alternative execution modes with advantages in cost-effectiveness. On Ethereum, we propose a holistic middleware platform supporting flexible and secure transaction executions, including off-chain states and batching of user requests. Furthermore, we propose control-plane schemes to adapt the execution mode to the current workload for optimal runtime cost. We present a case study on the institutional accounts (e.g., coinbase.com) intensively sending Ether on Ethereum blockchains. By collecting real-life transactions, we construct workload benchmarks and show that our work saves 18%\sim 47%18%-47% per invocation than the default baseline while introducing 1.81%\sim 16.59%1.81%-16.59% blocks delay.
Ethereum is a framework for cryptocurrencies which uses blockchain technology to provide an open global computing platform, called the Ethereum Virtual Machine (EVM). EVM executes bytecode on a simple stack machine. Programmers do not usually write EVM code; instead, they can program in a JavaScript-like language, called Solidity, that compiles to bytecode. Since the main purpose of EVM is to execute smart contracts that manage and transfer digital assets (called Ether), security is of paramount importance. However, writing secure smart contracts can be extremely difficult: due to the openness of Ethereum, both programs and pseudonymous users can call into the public methods of other programs, leading to potentially dangerous compositions of trusted and untrusted code. This risk was recently illustrated by an attack on TheDAO contract that exploited subtle details of the EVM semantics to transfer roughly $50M worth of Ether into the control of an attacker.
This paper introduces a concept of autonomous blockchain based negotiation to select the most convenient electric vehicle charging station. The enabling blockchain technologies are well known fundament of cryptocurrencies, but offer many other possible applications areas, such as automated trusted machine-to-machine transactions, including auctions, bidding and payments. Compared to traditional centralized approaches, such a solution does not require any central entities and can be fully automated, including the payment for the energy. Based on e.g. the planned route, car battery status, realtime traffic information and drivers' preferences, a car could request charging bids from various charging stations along the route, by executing blockchain based smart contracts related to these charging stations. It would then select the most appropriate one based on offered prices, but other input parameters could be also taken into account, e.g. waiting times, estimated charging duration and alike. The smart contract execution could be extended to reservation and payment, too. In the paper we briefly present blockchain technologies, with the focus on Ethereum, and explain the role of smart contracts. We outline the architecture of a simple system for autonomous selection for electric vehicle charging station and provide a UML model to depict the activities of the actors involved in these operations and to clarify the role and the requirements of various blockchain related entities. The aim of our research paper is to outline a possible use-case for a blockchain prototype implementation. The implementation, which is not presented here, will serve for investigation of practical aspects of smart node development and operation, like transaction performance measurements, practical system requirement evaluations and comparison of reliability of various Ethereum clients. By our research we hope to support the investigation of novel applications and blending Internet of things with blockchain technologies, and in particular for elaboration of possible new use cases in the domain of electrical energy and mobility.
Motivated by the great success and adoption of Bitcoin, a number of cryptocurrencies such as Litecoin, Dogecoin, and Ethereum are becoming increasingly popular. Although existing blockchain-based cryptocurrency schemes can ensure reasonable security for transactions, they do not consider any notion of fairness. Fair exchange allows two players to exchange digital items, such as digital signatures, over insecure networks fairly, so that either each player gets the other's item, or neither player does. Given that blockchain participants typically do not trust each other, enabling fairness in existing cryptocurrencies is an essential but insufficiently explored problem. In this paper, we explore the solution space for enabling the fair exchange of a cryptocurrency payment for a receipt. We identify the timeliness of an exchange as an important property especially when one of the parties involved in the exchange is resource-constrained. We introduce the notion of strong timeliness for a fair exchange protocol and propose two fair payment-for-receipt protocol instantiations that leverage functionality of the blockchain to achieve strong timeliness. We implement both and compare their security and efficiency.
Motivated by the great success and adoption of Bitcoin, a number of cryptocurrencies such as Litecoin, Dogecoin, and Ethereum are becoming increasingly popular. Although existing blockchain-based cryptocurrency schemes can ensure reasonable security for transactions, they do not consider any notion of fairness. Fair exchange allows two players to exchange digital "items", such as digital signatures, over insecure networks fairly, so that either each player gets the other's item, or neither player does. Given that blockchain participants typically do not trust each other, enabling fairness in existing cryptocurrencies is an essential but insufficiently explored problem. In this paper, we explore the solution space for enabling the fair exchange of a cryptocurrency payment for a receipt. We identify the timeliness of an exchange as an important property especially when one of the parties involved in the exchange is resource-constrained. We introduce the notion of strong timeliness for a fair exchange protocol and propose two fair payment-for-receipt protocol instantiations that leverage functionality of the blockchain to achieve strong timeliness. We implement both and compare their security and efficiency.
Benjamin Leiding, Parisa Memarmoshrefi, Dieter Hogrefe
Combining Vehicle Ad-hoc Networks (VANETs) and Ethereum's blockchain-based application concepts enables transparent, self-managed and decentralized system which are self-regulating and in no need of a central managing authority.
Die Möglichkeit der Programmierbarkeit des Bitcoins ist fast ein nachträglicher Einfall, auch wenn Sidechain‐Vorschläge diese Programmierbarkeit ein wenig leichter machen wollen und es bereits Altcoins mit verschiedenen spezifischen Anwendungen gibt. Im Gegensatz dazu wurde das Kryptowährungstechnologieprojekt Ethereum von Vitalik Buterin, seinem Erfinder, von Tag 1 als Software‐Entwicklungsplattform für dezentrale Applikationen konzipiert, und ihre Blockchain wurde speziell entwickelt, um die Ausführung dieser dezentralen Apps (auch Dapps genannt) zu unterstützen. Vitalik Buterin, 1994 in Russland geboren, war vor der Gründung von Ethereum auch involviert in die Entwicklungsprojekte Colored Coins und Mastercoins. Er gewann 2014 den "World Technology Award" und ein Stipendium des Risikokapitalgebers Peter Thiel. In dem Diskussionspapier zu Ethereum skizzierte Buterin vor allem die Grenzen einer Programmierbarkeit der Bitcoin‐Blockchain und schlug die Erstellung einer neuen komplett programmierbaren Blockchain mit einer turing‐vollständigen Programmiersprache vor. Anders als andere Blockchain‐Projekte soll die Ethereum Software nicht nur für einen Zweck nutzbar sein – sondern soll die Basis für die Erarbeitung aller möglichen Arten von Lösungen sein und dabei die Umsetzung intelligenter Verträge (Smart Contracts) ebenso erfassen als auch die Ethereum‐spezifische Idee von dezentralen autonomen Organisationen (DAOs).
Luke Anderson, Ralph Holz, Alexander Ponomarev, Paul Rimba · 5 authors
Half a decade after Bitcoin became the first widely used cryptocurrency, blockchains are receiving considerable interest from industry and the research community. Modern blockchains feature services such as name registration and smart contracts. Some employ new forms of consensus, such as proof-of-stake instead of proof-of-work. However, these blockchains are so far relatively poorly investigated, despite the fact that they move considerable assets. In this paper, we explore three representative, modern blockchains---Ethereum, Namecoin, and Peercoin. Our focus is on the features that set them apart from the pure currency use case of Bitcoin. We investigate the blockchains' activity in terms of transactions and usage patterns, identifying some curiosities in the process. For Ethereum, we are mostly interested in the smart contract functionality it offers. We also carry out a brief analysis of issues that are introduced by negligent design of smart contracts. In the case of Namecoin, our focus is how the name registration is used and has developed over time. For Peercoin, we are interested in the use of proof-of-stake, as this consensus algorithm is poorly understood yet used to move considerable value. Finally, we relate the above to the fundamental characteristics of the underlying peer-to-peer networks. We present a crawler for Ethereum and give statistics on the network size. For Peercoin and Namecoin, we identify the relatively small size of the networks and the weak bootstrapping process.
This paper examines three alternative architectures for financial ledgers: (1) centralised databases, (2) bitcoin-style blockchains and (3) Ethereum-style blockchains. It outlines the transaction model for these three types of ledger, covering both one-way payments and two-way atomic exchanges (delivery versus payment). Of particular note is how these architectures assign responsibility for maintaining the integrity of the ledger, to ensure that transactions do not create or delete funds and only move assets with the proper authorisation of their owners. Although Ethereum-style blockchains have many similarities to centralised databases with stored procedures, bitcoin-style blockchains are fundamentally different both at the ledger and transaction level.
Tendermint is a new protocol for ordering events in a distributed network under adversarial conditions. More commonly known as consensus or atomic broadcast, the problem has attracted significant attention recently due to the widespread success of digital currencies, such as Bitcoin and Ethereum, which successfully solve the problem in public settings without a central authority. Tendermint modernizes classic academic work on the subject to provide a secure consensus protocol with accountability guarantees, as well as an interface for building arbitrary applications above the consensus. Tendermint is high performance, achieving thousands of transactions per second on dozens of nodes distributed around the globe, with latencies of about one second, and performance degrading moderately in the face of adversarial attacks.
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.
The original purpose of this project was to research the capabilities of a relatively new cryptocurrency platform known as Ethereum. Extensive research brought to light Ethereum’s wide range of developmental capabilities and shifted our focus to the consideration of how the features that Ethereum offers can be used to improve some of the flaws within the world of cryptocurrency. Some cryptocurrency users find these systems useful, because it gives them a means of anonymity. This makes it pretty easy to launder money, make illegal purchases, and double spend. Our solution solves all of these issues, by tying a digital currency transaction to a specific purchase in a secure, untouchable, immutable means due to the blockchain’s proof of work. This solution was implemented through use of both blockchain technologies and a programmable “contract.” This contract adds additional data to cryptocurrency transactions. Our contract creates fields and storage that users can use to input dates, product numbers, product names, and notes that are directly associated with their transaction. Once these fields along with a transaction are deployed onto the blockchain, the information can be accessed using the definition or signature of the contract and the address on the block chain to which it is located. This adds the ability to claim warranty, check inventory, catch double spending instances, prevent black market spends, and help many other scenarios because there exists a publicly available proof of the purchase.
Bitcoin ilk merkezi olmayan, eşler arası ve en çok bilenen kripto paradır. Kripto paralar bir çeşit dijital paralar olup sanal para olarak da adlandırılır. Bitcoin 2009 da kullanılmaya başlandı ve bu tarihten itibaren büyük bir ilgi gördü. Geliştiriciler ve kullanıcılar tarafından büyük yatırımlar ve büyük katkılar sağlandı. Paranın yönetilmesi için bir merkeze bağlı olan günümüzde kullanılan paraya alternatif olarak kullanıma sunuldu. Fakat bu süre zarfında Bitcoin birçok problemle karşılaştı. Bunlara rağmen yaklaşık yedi senede çok büyük bir pazara sahip oldu. Bitcoin'in başarılı çıkışından sonra farklı amaçlara hizmet eden bir çok alternatif kripto para geliştirildi. Geliştiriciler Bitcoin'in bir çok farklı versiyonlarını geliştirdi. Bunlardan bazıları, Litecoin gibi Bitcoin'in kaynak kodunu kullanarak geliştirildi. Bazı kripto paralar Zcash, Ripple, Peercoin Bitcoin'in mahremiyet, ölçeklenebilirlik, enerji tüketimi gibi farklı eksikliklerinin üstesinden gelmek için geliştirildi. Bazıları ise, Ethereum, Namecoin, Colored Coin gibi, blockchain denen herkese açık kayıt sistemi fikrini kullanarak yenilikçi fikirler getirdi. Her geçen gün yeni kripto paralar kullanıma hazır hala getiriliyor ve bu teknoloji gelecekte şu anda kullanılan paranın yerini alacağı tahmin ediliyor. Bu tezde, Bitcoin ve alternatif kripto paralar tartışıldı ve mahremiyet, ölçeklenebilirlik, ticari işlem değiştirilebilirliği ve şu ana kadar maruz kaldıkları, savunmasız oldukları ataklar açısından karşılaştırıldılar. Gelecekteki durumları tartışılarak, gelecekte yapılacak işlerin planı yapılarak bu çalışma tamamlanmış oldu.
Blockchains and Byzantine Fault Tolerance form the basis of decentralized currencies and ledgers such as Bitcoin, Ripple, ZeroCash, and Ethereum. A large slate of literature has focused on the currency aspects (e.g. anonymity, independence from central banks, etc.). We argue that, as-far-as Distributed Payment Transactions Networks (PTNs) are concerned, there are other, possibly more interesting, properties. This paper provides a systematic review of both traditional PTNs and their analogues in decentralized ledgers and associates different technological features to the corresponding business and financial requirements. We provide a conceptual classification of the key properties (value creation, payment promise, transaction fulfillment, and value preservation). We map existing (distributed) PTNs into the classification showing different alternatives are possible. Furthermore, the ideas behind distributed ledgers can be extended beyond payments and contracts. We illustrate the idea of derivatives-contracts-as-programs that are marked to market (or an account that is margined) automatically by computations run on, and whose ownership transitions are recorded, in a distributed payment network.