Yackolley Amoussou-Guenou, Bruno Biais, Maria Potop-Butucaru, Sara Tucci-Piergiovanni
In this paper we analyze from the game theory point of view Byzantine Fault Tolerant blockchains when processes exhibit rational or Byzantine behavior. Our work is the first to model the Byzantine-consensus based blockchains as a committee coordination game. Our first contribution is to offer a game-theoretical methodology to analyse equilibrium interactions between Byzantine and rational committee members in Byzantine Fault Tolerant blockchains. Byzantine processes seek to inflict maximum damage to the system, while rational processes best-respond to maximise their expected net gains. Our second contribution is to derive conditions under which consensus properties are satisfied or not in equilibrium. When the majority threshold is lower than the proportion of Byzantine processes, invalid blocks are accepted in equilibrium. When the majority threshold is large, equilibrium can involve coordination failures , in which no block is ever accepted. However, when the cost of accepting invalid blocks is large, there exists an equilibrium in which blocks are accepted iff they are valid.
Smart contracts, which are widely recognized as key components of blockchain technology, enable automatic execution of agreements. Since each smart contract is a computer program that autonomously runs on a blockchain platform, their development requires much effort and care compared with the development of more common programs. In this paper, we propose a technique to automatically generate a smart contract from a human-understandable contract document that is created using a document template and a controlled natural language (CNL). The automation is based on a mapping from the document template and the CNL to a formal model that can define the terms and conditions in a contract including temporal constraints and procedures. The formal model is then translated into an executable smart contract. We implemented a toolchain that generates smart contracts of Hyperledger Fabric from template-based contract documents via a formal model. We then evaluated the feasibility of our approach through case studies of two types of real-world contracts in different domains.
With the advent of blockchain technology and the increasing penetration of rooftop photovoltaic (PV) systems, a new opportunity for energy trading through smart contracts has emerged. Challenges arise in such transactive markets to ensure individual rationality, incentive compatibility, budget balance, and economic efficiency during the auction process. This paper presents a comparative analysis of different smart contracts for solar electricity exchange in terms of market demand and supply metrics. Auction mechanisms considered in this paper are discriminatory and uniform k-Double Auction (k-DA). A simulation case study of 100 participants in a microgrid is presented using typical residential load and solar PV generation profiles. Results indicate that the discriminatory k-DA mechanism has the highest average percentage of contracts cleared and quantity traded during the period of excess solar energy generation, regardless of the level of PV penetration.
In Ethereum, many accounts and funds have been managed by smart contracts, thereby making them easy to be targeted. Due to the persistence characteristic of blockchain, revising a deployed smart contract is almost impossible. Both realities heighten the risks of managing funds and thus increase the demand for conducting sufficient testing to Ethereum Smart Contracts (ESC). Different from the conventional software, ESC is a gas-driven program, where developers must charge gases for deploying and testing it. Therefore, it is important to provide a cost-effective yet representative test suite, where its representativeness can be typically measured by its branch coverage. In this paper, we deem the problem of ESC test generation as a Pareto minimization problem, and three objectives, minimizing (1) uncovered branch coverage, (2) time cost, and (3) gas cost are considered. Then, we propose a random based and an NSGA-II based multi-objective approach to seek cost-effective test-suites. Our empirical study on a set of smart contracts in eight of the most widely used Ethereum Decentralized Applications (DApps) verified that the proposed approaches could significantly reduce the gas cost as well as the time cost while retaining the ability to cover branches.
We model the competition over several blockchains characterizing multiple cryptocurrencies as a non-cooperative game. Then, we specialize our results to two instances of the general game, showing properties of the Nash equilibrium. In particular, leveraging results about congestion games, we establish the existence of pure Nash equilibria and provide efficient algorithms for finding such equilibria.
We showcase our approach to verify off-chained information using Linked Data, Smart Contracts, and RDF graph hashes stored on a Distributed Ledger. In this demo, we present our implementation and a use case from the supply chain domain.
Nylig lansert åpen kildekode blokkjede mellomvareteknologi kalt Chainlink har gjort det mulig å enkelt kombinere og koble smarte kontrakter sammen med eksterne systemer med varierende grad av sikkerhet og pålitelighet. Måten dette oppnås på er ved å koble de smarte kontraktene sammen med flere tredjeparter eller ”orakler” som tilbyr tjenesten å knytte smart kontrakten til det eksterne\nsystemet.\n\nDenne oppgaven tar for seg om det er etterspørsel for og hvordan kunstig intelligens kan bli solgt til og kombinert i smarte konrakter på en måte som minimerer behovet for tillit. For å gjøre dette blir markedet og økosystemet rundt Chainlink nettverket beskrevet. Ulike orakeltyper i Chainlink nettverket blir identifisert og det blir identifisert at det ikke er et umiddelbar mulighet å selge til kunstig intelligens til smarte kontrakter i dag på grunn av at teknologien fortsatt er umoden og nødvendig infrastruktur fortsatt mangler.\n\nVidere så blir det identifisert flere måter å kombinere smarte kontrakter med kunstig intelligens ved hjelp av orakler og at det finnes måter hvor kravet til tillit er minimalt. For å motivere leseren blir det gitt eksempler på bruksområder for kunstig intelligens og smarte kontrakter i introduksjonskapittelet og disse blir gjenbesøkt senere i oppgaven hvor de relateres opp mot kombinasjonene av kunstig intelligens og smarte kontrakter som er funnet.
Amjad Saeed Khan, Yogachandran Rahulamathavan, Bokamoso Basutli, Gan Zheng · 6 authors
Physical layer security (PLS) is considered as a promising technique to prevent information eavesdropping in wireless systems. In this context, cooperative relaying has emerged as a robust solution for achieving PLS due to multipath diversity and relatively lower transmission power. However, relays or the relay operators in the practical environment are unwilling for service provisioning unless they are incentivized for their cost of services. Thus, it is required to jointly consider network economics and relay cooperation to improve system efficiency. In this paper, we consider the problem of joint network economics and PLS using cooperative relaying and jamming. Based on the double auction theory, we model the interaction between transmitters seeking for a particular level of secure transmission of information and relay operators for suitable relay and jammer assignment, in a multiple source-destination networks. In addition, theoretical analyses are presented to justify that the proposed auction mechanism satisfies the desirable economic properties of individual rationality, budget balance, and truthfulness. As the participants in the traditional centralized auction framework may take selfish actions or collude with each other, we propose a decentralized and trustless auction framework based on blockchain technology. In particular, we exploit the smart contract feature of blockchain to construct a completely autonomous framework, where all the participants are financially enforced by smart contract terms. The security properties of the proposed framework are also discussed.
Smart contracts on a blockchain network can be implemented to control digital value. A key question that arises is the extent to which smart contracts can, or should, operate as "smart legal contracts". Simply put, can smart contracts meet requirements of validity at law and practical efficacy. In order to achieve the goal of value maximization, the efforts of policy-makers, standards organisations and regulators should be informed by first principles. Standards, and other regulatory activities, must be driven by consideration of the technolegal functions of contracting. Blockchain-based smart contracts offer the potential to reduce transaction costs through new methods of stateful computation. When applied to commercial transactions, smart contracts can represent enforcement of an executed state. This paper argues that distributed ledger and smart contracts standards should seek to provide sufficient flexibility to facilitate contracting parties to coordinate in an optimal manner.
Dominik Harz, Lewis Gudgeon, Arthur Gervais, William J. Knottenbelt
Financial deposits are fundamental to the security of cryptoeconomic protocols as they serve as insurance against potential misbehaviour of agents. However, protocol designers and their agents face a trade-off when choosing the deposit size. While substantial deposits might increase the protocol security, for example by minimising the impact of adversarial behaviour or risks of currency fluctuations, locked-up capital incurs opportunity costs. Moreover, some protocols require over-collateralization in anticipation of future events and malicious intentions of agents. We present Balance, an application-agnostic system that reduces over-collateralization without compromising protocol security. In Balance, malicious agents receive no additional utility for cheating once their deposits are reduced. At the same time, honest and rational agents increase their utilities for behaving honestly as their opportunity costs for the locked-up deposits are reduced. Balance is a round-based mechanism in which agents need to continuously perform desired actions. Rather than treating agents' incentives and behaviour as ancillary, we explicitly model agents' utility, proving the conditions for incentive compatibility. Balance improves social welfare given a distribution of honest, rational, and malicious agents. Further, we integrate Balance with a cross-chain interoperability protocol, XCLAIM, reducing deposits by 10% while maintaining the same utility for behaving honestly. Our implementation allows any number of agents to be maintained for at most 55,287 gas (ca. USD 0.07) to update all agents' scores, and at a cost of 54,948 gas (ca. USD 0.07) to update the assignment of all agents to layers.
We study optimal smart contract design for monitoring an exchange of an item performed offline. There are two parties, a seller and a buyer. Exchange happens off-chain, but the status update takes place on-chain. The exchange can be verified but with a cost. To guarantee self-enforcement of the smart contract, both parties make a deposit, and the deposits must cover payments made in all possible final states. Both parties have an (opportunity) cost of making deposits. We discuss two classes of contract: In the first, the mechanism only interacts with the seller, while in the second, the mechanism can also interact with the buyer. In both cases, we derive optimal contracts specifying optimal deposits and verification policies. The gains from trade of the first contract are dominated by the second contract, on the whole domain of parameters. However, the first type of contract has the advantage of less communication and, therefore, more flexibility.