Lin Chen, Lei Xu, Zhimin Gao, Nolan Shah · 6 authors
Transaction system build on top of blockchain, especially smart contract, is becoming an important part of world economy. However, there is a lack of formal study on the behavior of users in these systems, which leaves the correctness and security of such system without a solid foundation. Unlike mining, in which the reward for mining a block is fixed, different execution results of a smart contract may lead to significantly different payoffs of users, which gives more incentives for some user to follow a branch that contains a wrong result, even if the branch is shorter. It is thus important to understand the exact probability that a branch is being selected by the system. We formulate this problem as the (+-)-Biased Ballot Problem as follows: there are n voters one by one voting for either of the two candidates A and B. The probability of a user voting for A or B depends on whether the difference between the current votes of A and B is positive or negative. Our model takes into account the behavior of three different kinds of users when a branch occurs in the system -- users having preference over a certain branch based on the history of their transactions, and users being indifferent and simply follow the longest chain. We study two important probabilities that are closely related with a blockchain based system - the probability that A wins at last, and the probability that A receives d votes first. We show how to recursively calculate the two probabilities for any fixed n and d, and also discuss their asymptotic values when n and d are sufficiently large.
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>
Mining for Bitcoins is a high-risk high-reward activity. Miners, seeking to reduce their variance and earn steadier rewards, collaborate in pooling strategies where they jointly mine for Bitcoins. Whenever some pool participant is successful, the earned rewards are appropriately split among all pool participants. Currently a dozen of different pooling strategies (i.e., methods for distributing the rewards) are in use for Bitcoin mining. We here propose a formal model of utility and social welfare for Bitcoin mining (and analogous mining systems) based on the theory of discounted expected utility, and next study pooling strategies that maximize the social welfare of miners. Our main result shows that one of the pooling strategies actually employed in practice--the so-called geometric pay pool--achieves the optimal steady-state utility for miners when its parameters are set appropriately. Our results apply not only to Bitcoin mining pools, but any other form of pooled mining or crowdsourcing computations where the participants engage in repeated random trials towards a common goal, and where "partial" solutions can be efficiently verified.
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.
Modern economies are held together by innumerable contracts. However, current contracts are neither machine-readable nor easily human-readable. The Ricardian Contract paradigm of parameters, prose and code posits a hybrid model of automation and conventional legal text. This paper connects recent work on design criteria for 'Smart Contract Templates' with prose objects and prototype inheritance demonstrated at CommonAccord. Templates authored and shared as prose objects can become the basis for automation, codification, commentary, big data analysis and graphic presentations.
The blockchain constitutes a technology-based, rather than social or regulation based, means to lower uncertainty about one another in order to exchange value. However, its use may very well also lead to increased complexity resulting from having to subsume work that displaced intermediary institutions had performed. We present our perspective that smart contracts may be used to mitigate this increased complexity. We further posit that smart contracts can be delineated according to complexity: Smart contracts that can be verified objectively without much uncertainty belong in an inter- organizational context; those that cannot be objectively verified belong in an intra- organizational context. We state that smart contracts that implement a formal (e.g. mathematical or simulation) model are especially beneficial for both contexts: They can be used to express and enforce inter-organizational agreements, and their basis in a common formalism may ensure effective evaluation and comparison between different intra-organizational contracts. Finally, we present a case study of our perspective by describing Intellichain, which implements formal, agent-based simulation model as a smart contract to provide epidemiological decision support.
Daniele Magazzeni, Peter McBurney, William L. Nash
Smart contracts might encode legal contracts written in natural language to represent the contracting parties' shared understandings and intentions. The issues and research challenges involved in the validation and verification of smart contracts, particularly those running over blockchains and distributed ledgers, are explored.
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.
The aim of this chapter is to situate blockchain-based governance tools within a public value (PV) context, arguing that public governance on the blockchain requires elements of a “public value mindset,” which is comprised of transparency, efficiency, stakeholder salience and participation, innovative thinking, decentralization, and trust. To illustrate this PV mindset, the chapter analogizes the powerful solution put forth by cryptocurrencies towards the “double spending problem,” an issue that had once plagued electronic money, by arguing that the manner in which the double-spending problem was solved by blockchain technology (as best embodied by cryptocurrencies) also offers lessons for public governance on the blockchain, specifically in terms of the PV elements enumerated above. By elucidating the nature of the double-spending problem and the revolutionary solution offered by cryptocurrencies, the chapter advocates for a similar approach in the application of blockchain technologies to public management and governance.
On-line commercial transactions involve an inherent mistrust between participant parties since, sometimes, no previous relation exists between them. Such mistrust may be a deadlock point in a trade transaction where the buyer does not want to perform the payment until the seller sends the goods and the seller does not want to do so until the buyer pays for the purchase. In this paper we present a fair protocol for data trading where the commercial deal, in terms of delivering the data and performing the payment, is atomic, since the seller cannot redeem the payment unless the buyer obtains the data and the buyer cannot obtain the data without performing the payment. The protocol is based on Bitcoin scripting language and the fairness of the protocol can be probabilistically enforced.
Investor and media attention in Bitcoin has increased substantially in recently years, reflected by the incredible surge in news articles and considerable rise in the price of Bitcoin. Given the increased attention, there little is known about the behaviour of Bitcoin prices and therefore we add to the literature by studying price clustering. We find significant evidence of clustering at round numbers, with over 10% of prices ending with 00 decimals compared to other variations but there is no significant pattern of returns after the round number. We also support the negotiation hypothesis of Harris (1991) by showing that price and volume have a significant positive relationship with price clustering at whole numbers.
Distributed ledger technology (DLT) is a database architecture which enables the keeping and sharing of records in a distributed and decentralized way, while ensuring its integrity through the use of consensus-based validation protocols and cryptographic signatures. In principle, DLT has the potential to reduce costs and increase the efficiency of securities settlement, the ultimate step of every security transaction. In this paper, we first examine to what extent DLT could add value and change securities settlement. We then characterize the innovation process in the post-trade industry and finally, we describe the economics of a hypothetical DLT-based security settlement industry. Our main conclusions are that: i) DLT has the potential to improve efficiency and reduce costs in securities settlement, but the technology is still evolving and it is uncertain at this point what form, if any, a DLT-based solution for securities settlement will ultimately take, ii) technological innovation in the post-trade industry is more likely to achieve its potential with some degree of co-ordination which could be facilitated by the relevant authorities, and iii) if DLT-based securities settlement becomes a reality, then it is likely to be concentrated among few providers which, in the absence of regulation, could result in inefficient monopoly pricing or efficient price discrimination with service providers capturing much of the market surplus.
Sinclair Davidson, Primavera De Filippi, Jason Potts
Abstract Blockchains are a new digital technology that combines peer-to-peer network computing and cryptography to create an immutable decentralised public ledger. Where the ledger records money, a blockchain is a cryptocurrency, such as Bitcoin; but ledger entries can record any data structure, including property titles, identity and certification, contracts, and so on. We argue that the economics of blockchains extend beyond analysis of a new general purpose technology and its disruptive Schumpeterian consequences to the broader idea that blockchains are an institutional technology. We consider several examples of blockchain-based economic coordination and governance. We claim that blockchains are an instance of institutional evolution.
Blockchain technology provides decentralized consensus and potentially enlarges the contracting space through smart contracts. Meanwhile, generating decentralized consensus entails distributing information that necessarily alters the informational environment. We analyze how decentralization relates to consensus quality and how the quintessential features of blockchain remold the landscape of competition. Smart contracts can mitigate informational asymmetry and improve welfare and consumer surplus through enhanced entry and competition, yet distributing information during consensus generation may encourage greater collusion. In general, blockchains sustain market equilibria with a wider range of economic outcomes. We further discuss the implications for antitrust policies targeted at blockchain applications. Received May 31, 2017; editorial decision May 29, 2018 by Editor Itay Goldstein.
Orphan risk for large blocks limits Bitcoin’s transactional capacity while the lack of secure instant transactions restricts its usability. Progress on either front would help spur adoption. This paper considers a technique for using fractional-difficulty blocks (weak blocks) to build subchains bridging adjacent pairs of real blocks. Subchains reduce orphan risk by propagating blocks layer-by-layer over the entire block interval, rather than all at once when the proof-of-work is solved. Each new layer of transactions helps to secure the transactions included in lower layers, even though none of the transactions have been con-firmed in a real block. Miners are incentivized to cooperate building subchains in order to process more transactions per second (thereby claiming more fee revenue) without incur-ring additional orphan risk. The use of subchains also diverts fee revenue towards network hash power rather than dripping it out of the system to pay for orphaned blocks. By nesting subchains, weak block verification times approaching the theoretical limits imposed by speed-of-light constraints would become possible with future technology improvements. As subchains are built on top of the existing Bitcoin protocol, their implementation does not require any changes to Bitcoin’s consensus rules.
Aggelos Kiayias, Ηλίας Κουτσουπιάς, Maria Kyropoulou, Yiannis Tselekounis
We study the strategic considerations of miners participating in the bitcoin's protocol. We formulate and study the stochastic game that underlies these strategic considerations. The miners collectively build a tree of blocks, and they are paid when they create a node (mine a block) which will end up in the path of the tree that is adopted by all. Since the miners can hide newly mined nodes, they play a game with incomplete information. Here we consider two simplified forms of this game in which the miners have complete information. In the simplest game the miners release every mined block immediately, but are strategic on which blocks to mine. In the second more complicated game, when a block is mined it is announced immediately, but it may not be released so that other miners cannot continue mining from it. A miner not only decides which blocks to mine, but also when to release blocks to other miners. In both games, we show that when the computational power of each miner is relatively small, their best response matches the expected behavior of the bitcoin designer. However, when the computational power of a miner is large, he deviates from the expected behavior, and other Nash equilibria arise.
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.
We analyze how network effects affect competition in the nascent cryptocurrency market. We do so by examining early dynamics of exchange rates among different cryptocurrencies. While Bitcoin eventually dominates this market, our data suggest no evidence of a winner-take-all effect early in the market. Indeed, for a relatively long period, a few other cryptocurrencies competing with Bitcoin (the early industry leader) appreciated much more quickly than Bitcoin. The data in this period are consistent with the use of cryptocurrencies as financial assets (popularized by Bitcoin), and not consistent with winner-take-all dynamics. Toward the end of our sample, however, things change dramatically. Bitcoin appreciates against the USD, while other currencies depreciate against the USD. The data in this period are consistent with strong network effects and winner-take-all dynamics. This trend continues as at the time of writing.
We document systematic differences in bitcoin prices across 11 different markets representing 26% of global bitcoin trade volume. These differences must -due to the identical nature of all bitcoin -result from characteristics of markets themselves. We examine differences across the markets and find that those which do not require customer identification for establishing an account are more likely to deviate from representative market prices than those which do. This implies that standard financial regulations, specifically know-your-customer regulations, can have a non-negligible impact on the bitcoin market.