Blockchains address trust through cryptography and consensus. Bitcoin is the first digital currency without trusted agents. Ethereum extends this technology by enabling agents on a blockchain, via smart contracts. However, a systemic trust model for smart contracts in blockchains is missing. This thesis describes the ecosystem of smart contracts as an open multi-agent system. A trust model introduces social control through deposits and review agents. Trust-related attributes are quantified in 2,561 smart contracts from GitHub. Smart contracts employ a mean of three variables and functions and one in ten has a security-related issue. Moreover, blockchains restrict computation tasks. Resolving these restrictions while maintaining trust requires verifiable computation. An algorithm for verifiable computation is developed and implemented in Solidity. It uses an arbiter enforcing the algorithm, computation services providing and verifying solutions, and a judge assessing solutions. Experiments are performed with 1000 iterations for one to six verifiers with a cheater prior probability of 30%, 50%, and 70%. The algorithm shows linear complexity for integer multiplication. The verification depends on cheater prior probability and amount of verifiers. In the experiments, six verifiers are sufficient to detect all cheaters for the three prior probabilities.
Marc Sel, Henning Diedrich, Sander Demeester, Harald Stieber
This paper explains the main features of and motivation for the “report once” demonstrator1 shown at the 2017 Data For Policy conference. It shows how Ethereum2 smart contracts, based on the semantics and algorithmic representations defined in ACTUS3 can implement “digital doppelgängers” of financial contracts. <br> <br> The implementation makes use of a private4 Ethereum blockchain, with smart contracts written in Solidity.5 The limitations of using ACTUS in a semi real-time scenario are explored, as well as how to overcome these limitations. <br> <br> The major innovation, visualized by the demonstrator, is that compliance reports can be generated in semi realtime, using the information present in the “digital doppelgängers”, residing in the blockchain. <br> <br> The demonstrator supports various use cases, illustrated through the narration of stories. In these stories, Alice, Bob and Eve are contracting parties, Romeo acts as regulator, and the narrator tells the stories. The stories cover trading a Bond, trading an Interest Rate Swap (IRS), the defaulting of a party (i.e. a payment stop), and various types of regulatory reports. <br>
Financial technology (FinTech) is the new business model and technology which aims to compete with traditional financial services and blockchain is one of most famous technology use of FinTech. Blockchain is a type of distributed, electronic database (ledger) which can hold any information (e.g. records, events, transactions) and can set rules on how this information is updated. The most well-known application of blockchain is bitcoin, which is a kind of cryptocurrencies. But it can also be used in many other financial and commercial applications. A prominent example is smart contracts, for instance as offered in Ethereum. A contract can execute a transfer when certain events happen, such as payment of a security deposit, while the correct execution is enforced by the consensus protocol. The purpose of this paper is to explore the research and application landscape of blockchain technology acceptance by following a more comprehensive approach to address blockchain technology adoption. This research is to propose a unified model integrating Innovation Diffusion Theory (IDT) model and Technology Acceptance Model (TAM) to investigate continuance intention to adopt blockchain technology.
Cryptocurrencies allow users to securely transfer money without relying on a trusted intermediary, \nand the transparency of their underlying ledgers also enables public verifiability. This openness, \nhowever, comes at a cost to privacy, as even though the pseudonyms users go by are not linked to their \nreal-world identities, all movement of money among these pseudonyms is traceable. In this paper, \nwe present M¨obius, an Ethereum-based tumbler or mixing service. M¨obius achieves strong notions of \nanonymity, as even malicious senders cannot identify which pseudonyms belong to the recipients to \nwhom they sent money, and is able to resist denial-of-service attacks. It also achieves a much lower \noff-chain communication complexity than all existing tumblers, with senders and recipients needing \nto send only two initial messages in order to engage in an arbitrary number of transactions.
Cryptocurrencies and blockchains are increasingly used, implemented and adapted for numerous purposes; people and businesses are integrating these technologies into their practices and strategies, creating new political economies and spaces in and of everyday life. This thesis seeks to develop a foundation of geographic theory for the study of spatial production within and surrounding blockchain technologies focusing on acute studies of Bitcoin as cryptocurrency, Ethereum as digital marketplace, and their conditions of possibility as decentralized autonomous organizations. Utilizing concepts from Henri Lefebvre's Production of Space, this thesis situates blockchain technologies within the wider discussion about the political economy of modes of spatial production, dialectical material methods, code/space, and network society through an examination of human and machine relations within their unique and emergent spaces. Combining phenomenological and dialectical material methods with the methodological practice of discourse analysis and systems theory, this thesis explores an understanding of how systemic mechanisms and actant actions driving blockchain technologies are indications of new evolutions in our conceptions of space and place in everyday life of later informational capitalism.
D. O. Kondyrev, V. S. Bobrov, I. E. Efremov, V. N Vlasov
1. Свон М. Блокчейн: Схема новой экономики. М.: Олимп-Бизнес, 2017. 240 с.: ил.
2. Wattenhofer R. The Science of the Blockchain. 1st ed. Inverted Forest Publishing, 2016. 115 p.
3. Равал С. Децентрализованные приложения. Технология Blockchain в действии. СПб.: Питер, 2017. 240 с. : ил.
4. Antonopoulos A. M. Mastering Bitcoin. 1st ed. O’Reilly Media, 2014. 296 p.
5. Дейт К. Дж. Введение в системы баз данных. 8-е изд. М.: ИД «Вильямс», 2005. 1328 с.: ил.
6. Гарсия-Молина Г., Ульман Д., Уидом Д. Системы баз данных. Полный курс. М.: ИД «Вильямс», 2003. 1089 с.: ил.
7. Таненбаум Э., Стеен М. ван. Распределенные системы. Принципы и парадигмы. СПб.: Питер, 2003. 877 с.: ил.
Shayan Eskandari, Jeremy Clark, Vignesh Sundaresan, Moe Adham
In this paper, we present Velocity, a decentralized market deployed on Ethereum for trading a custom type of derivative option. To enable the smart contract to work, we also implement a price fetching tool called PriceGeth. We present this as a case study, noting challenges in development of the system that might be of independent interest to whose working on smart contract implementations. We also apply recent academic results on the security of the Solidity smart contract language in validating our codes security. Finally, we discuss more generally the use of smart contracts in modelling financial derivatives.
We discuss Russia's underlying motives for issuing its government-backed cryptocurrency, CryptoRuble, and the implications thereof and of other likely-soon-forthcoming government-issued cryptocurrencies to some stakeholders (populace, governments, economy, finance, etc.), existing decentralized cryptocurrencies (such as Bitcoin and Ethereum), as well as the future of the world monetary system (the role of the U.S. therein and a necessity for the U.S. to issue CryptoDollar), including a future algorithmic universal world currency that may also emerge. We further provide a comprehensive list of references on cryptocurrencies.
Digital currencies and cryptocurrencies have hesitantly started to penetrate the investors, and the next step will be the regulatory risk management framework. We examine the Value-at-Risk and Expected Shortfall properties for the major digital currencies, Bitcoin, Ethereum, Litecoin, and Ripple. The methodology used is GARCH modelling followed by Filtered Historical Simulation. We find that digital currencies are subject to a higher risk, therefore, to higher sufficient buffer and risk capital to cover potential losses.
We present efficient protocols for amortized secure multiparty computation with penalties and secure cash distribution, of which poker is a prime example. Our protocols have an initial phase where the parties interact with a cryptocurrency network, that then enables them to interact only among themselves over the course of playing many poker games in which money changes hands. The high efficiency of our protocols is achieved by harnessing the power of stateful contracts. Compared to the limited expressive power of Bitcoin scripts, stateful contracts enable richer forms of interaction between standard secure computation and a cryptocurrency. We formalize the stateful contract model and the security notions that our protocols accomplish, and provide proofs using the simulation paradigm. Moreover, we provide a reference implementation in Ethereum/Solidity for the stateful contracts that our protocols are based on. We also adopt our off-chain cash distribution protocols to the special case of stateful duplex micropayment channels, which are of independent interest. In comparison to Bitcoin based payment channels, our duplex channel implementation is more efficient and has additional features.
Since Bitcoin was launched in 2009, several new cryptocurrencies have been initiated with variations to Bitcoin's original design. Although Bitcoin still remains the most prominent actor in the market, some technical problems have been raised to the design of the protocol. The objective of this thesis is to determine whether the newer cryptocurrencies handle the technical problems of Bitcoin, or if they also suffer from the same issues. Instead of evaluating several cryptocurrencies for this comparison, the cryptocurrency Ethereum has been chosen as a proxy for the others. Ethereum was started in 2014, is widely backed in the community and is second in line to Bitcoin when it comes to market capitalization. \n\nAs a basis for the comparative analysis a rigorous study of the Bitcoin and Ethereum protocols have been performed, and parallel descriptions of the systems have been devised. Three technical problem have shaped the focus of the analysis: computational waste, concentration of power and ambiguity of transactions. Real world statistical data has been gathered and synthesized to enlighten the findings in the comparison. The main result of the comparison is that both systems suffer from the same problems to a certain degree, due to the fact that they utilize the same consensus mechanism. However, Ethereum utilizes several newer techniques to try and reduce the severity of these problems compared to Bitcoin, with varying degrees of success.
Massimo Bartoletti, Stefano Lande, Livio Pompianu, Andrea Bracciali
Modern cryptocurrencies exploit decentralised blockchains to record a public and unalterable history of transactions. Besides transactions, further information is stored for different, and often undisclosed, purposes, making the blockchains a rich and increasingly growing source of valuable information, in part of difficult interpretation. Many data analytics have been developed, mostly based on specifically designed and ad-hoc engineered approaches. We propose a general-purpose framework, seamlessly supporting data analytics on both Bitcoin and Ethereum --- currently the two most prominent cryptocurrencies. Such a framework allows us to integrate relevant blockchain data with data from other sources, and to organise them in a database, either SQL or NoSQL. Our framework is released as an open-source Scala library. We illustrate the distinguishing features of our approach on a set of significant use cases, which allow us to empirically compare ours to other competing proposals, and evaluate the impact of the database choice on scalability.
Blockchain technology as a whole is experiencing a dramatic rise in adoption, in no small part due to the developer-friendly Ethereum network. While the number of smart-contract powered distributed applications (Dapps) continues to rise, they face many of the same challenges all new technologies face as they are introduced to a market. By modeling the consumer adoption of blockchain technology and analyzing scholarly literature on supply-side factors affecting the diffusion of technology, we seek to prove the growth of a Dapp can be accelerated using abstraction, whole product planning, and complementaries.
Over past decade cloud services have enabled individuals and organizations to perform different types of tasks such as online storage, email services, on-demand movies and TV shows. The cloud services has also enabled on-demand deployment of applications, at cheap cost with elastic and scalable, fault tolerant system. These cloud services are offered by cloud providers who use authentication, authorization and accounting framework based on client-server model. Though this model has been used over decades, study shows it is vulnerable to different hacks and it is also inconvenient to use for the end users. In addition, the cloud provider has total control over user data which they are able to monitor, trace, leak and even modify at their will. Thus, the user data ownership, digital identity and use of cloud services has raised privacy and security concern for the users. In this thesis, Blockchain and its applications are studied and alternative model for authentication, authorization and accounting is proposed based on Ethereum Blockchain. Furthermore, a prototype is developed which enables users to consume cloud services by authenticating, authorizing and accounting with a single identity without sharing any private user data. Experiments are run with the prototype to verify that it works as expected. Measurements are done to assess the feasibility and scalability of the solution. In the final part of the thesis, pros and cons of the proposed solution are discussed and perspectives for further research are sketched.
This study provides a comparative financial and statistical analysis between the largest and most trad- ed cryptocurrencies. In particular, the exchange rates of Bitcoin, Litecoin, Ripple and Ethereum were collected from August 2010 until May 2017. The raw annualized volatility of cryptocurrencies is compared as well as to fiat currencies and major exchange rates. The results show that Bitcoin is the least volatile cryptocurrency with low correlations with the altcoins, providing possible diversification benefits to cryptocurrency investing. In addition, our results indicate that Bitcoin is the only cryptocurrency that has causality effects on the other cryptocurrencies.
In this paper, we explore remarkable similarities between multi-transactional behaviors of smart contracts in cryptocurrencies such as Ethereum and classical problems of shared-memory concurrency. We examine two real-world examples from the Ethereum blockchain and analyzing how they are vulnerable to bugs that are closely reminiscent to those that often occur in traditional concurrent programs. We then elaborate on the relation between observable contract behaviors and well-studied concurrency topics, such as atomicity, interference, synchronization, and resource ownership. The described contracts-as-concurrent-objects analogy provides deeper understanding of potential threats for smart contracts, indicate better engineering practices, and enable applications of existing state-of-the-art formal verification techniques.
Smart contracts are computer programs that can be consistently executed by a network of mutually distrusting nodes, without the arbitration of a trusted authority. Because of their resilience to tampering, smart contracts are appealing in many scenarios, especially in those which require transfers of money to respect certain agreed rules (like in financial services and in games). Over the last few years many platforms for smart contracts have been proposed, and some of them have been actually implemented and used. We study how the notion of smart contract is interpreted in some of these platforms. Focussing on the two most widespread ones, Bitcoin and Ethereum, we quantify the usage of smart contracts in relation to their application domain. We also analyse the most common programming patterns in Ethereum, where the source code of smart contracts is available.