Blockchain Papers

Pietro De Giovanni

No abstract is available for this record.

Ignacio Huitzil, Alvaro Fuentemilla, Fernando Bobillo

This paper proposes a novel extension of blockchain systems with fuzzy ontologies. The main advantage is to let the users have flexible restrictions, represented using fuzzy sets, and to develop smart contracts where there is a partial agreement among the involved parts. We propose a general architecture based on four fuzzy ontologies and a process to develop and run the smart contracts, based on a reduction to a well-known fuzzy ontology reasoning task (Best Satisfiability Degree). We also investigate different operators to compute Pareto-optimal solutions and implement our approach in the Ethereum blockchain.

Siyuan Wang, Xuehan Zhang, Wei Yu, Kai Hu · 5 authors

A smart contract is a computable protocol that automatically enforces contract terms in a computer, transforming real-world contract terms into digital promises of the virtual world. Early smart contracts have been stuck in the theoretical phase due to the lack of a credible execution environment and the means to control digital assets. With the emergence of blockchain technology, it has solved the problems mentioned above. Smart contracts are stored on blockchain, ensuring the credibility of contract execution through the joint execution of contracts by the various nodes in the blockchain network. However, the current technology of blockchain-based smart contracts is still not mature enough and faces many major challenges. Among them, the extensibility and performance of smart contracts are the most important and most concerned ones. This paper studies the extensibility and performance of smart contracts by combining blockchain-based smart contracts with cloud technologies to address the extensibility and performance issues of smart contracts. Combined with micro-service technology, a new type of smart contract architecture is proposed, and then the key technologies in each layer of the architecture are further studied.

Tam Bang, Hoang H. Nguyen, Dung Nguyen, Toan Trieu · 5 authors

Ethereum smart contracts based on blockchain technology are powerful and promising applications that provide a global platform for exchanging cryptocurrencies and public services. This technology are garnering a huge impact and is widely adopted in the current times as it can transform the way we transfer and exchange value by passing the need for a middleman and reducing cost. These smart contracts also represent a basis for true ownership of digital assets and a wide range of decentralized applications. Besides this, since Ethereum and its smart contracts are a publicly accessible, unchangeable and distributed platform, they are extremely vulnerable to various forms of attack, with their security becoming a top priority. However, current security-verifying programs tend to provide many technical details which are pretty hard for normal people to understand briefly. To tackle this problem, we designed a process aiming to mitigate these limitations, with our key insight being a combination of semantic structure analysis and symbolic execution on control-flow graphs (CFG for short). This article proposes a new approach for auditing Ethereum smart contracts, applying this technique would benefit both average users without any technical knowledge and security experts as well.

Refito Ilham

Voting has become one of the methods used by humans to determine decisions. Voting is also often used in determining something that are very important, such as determining people's representative council. In addition, the current voting is still using the Conventional system that uses paper in balloting, and vote counting. This can cause human error. The technology that is increasingly developing in the current era of globalization is e-voting. From this research, an e-vote system will be developed that applies the concept of the block chain node with smart contract. Smart contracts generate unique code for each new election. So that manipulation of election results will not be possible because each voter has only one account and one address block chain. From the results of the test the author can conclude that the smart contract block chain can be used to prove the results of a safe choice and create e-voting that is honest.

Itay Tsabary, Matan Yechieli, Alex Manuskin, Ittay Eyal

Smart Contracts and transactions allow users to implement elaborate constructions on cryptocurrency blockchains like Bitcoin and Ethereum. Many of these constructions, including operational payment channels and atomic swaps, use a building block called Hashed Time-Locked Contract (HTLC). In this work, we distill from HTLC a specification (HTLC-Spec), and present an implementation called Mutual-Assured-Destruction Hashed Time-Locked Contract (MAD-HTLC). MAD-HTLC employs a novel approach of utilizing the existing blockchain operators, called miners, as part of the design. If a user misbehaves, MAD-HTLC incentivizes the miners to confiscate all her funds. We prove MAD-HTLC's security using the UC framework and game-theoretic analysis. We demonstrate MAD-HTLC's efficacy and analyze its overhead by instantiating it on Bitcoin's and Ethereum's operational blockchains. Notably, current miner software makes only little effort to optimize revenue, since the advantage is relatively small. However, as the demand grows and other revenue components shrink, miners are more motivated to fully optimize their fund intake. By patching the standard Bitcoin client, we demonstrate such optimization is easy to implement, making the miners natural enforcers of MAD-HTLC. Finally, we extend previous results regarding HTLC vulnerability to bribery attacks. An attacker can incentivize miners to prefer her transactions by offering high transaction fees. We demonstrate this attack can be easily implemented by patching the Bitcoin client, and use game-theoretic tools to qualitatively tighten the known cost bound of such bribery attacks in presence of rational miners. We identify bribe opportunities occurring on the Bitcoin and Ethereum main networks where a few dollars bribe could yield tens of thousands of dollars in reward (e.g., \$2 for over \$25K).

Dabao Wang, Kui Liu, Li Li

When the execution of smart contracts fails, the transaction will not be recorded to provide hints for analysts to improve their automated analyzers. To mitigate this, we present ExecuWatch to watch the execution of smart contracts and report the execution details.

Fabian Schär

Blockchain forks can have severe economic implications, sow uncertainty and undermine trust. In this paper, we introduce a formal framework to study the emergence, persistency and economic consequences of blockchain forks. We argue that blockchain forks can be process- or protocol-based and emerge unintentionally or deliberately. We then proceed with a sub-classification of protocol-based forks and study the circumstances under which a chain split may become permanent. It can be shown that the persistency of a fork depends on the nature of the change to the consensus rules and on the relative allocation of the consensus-relevant resources. Lastly, we discuss business implications as well as potential consequences for policy makers and practitioners.

Keerthi Nelaturu, John R. Adler, Marco Merlini, Ryan Berryhill · 7 authors

Blockchain technology has created an excitement that was last seen two decades ago when the Internet was entering the mainstream. An appealing feature of blockchain technology is smart contracts. A smart contract is an executable code. It runs on top of the blockchain facilitating an agreement between untrusted parties. These smart contracts have a major limitation, namely they cannot operate on information external to the blockchain. The inability to query such information has paved the need for trusted entities called “oracles.” These oracles attest to facts without the robust security guarantees that blockchains generally provide. This can potentially harm the integrity of the network and lead to centralized points-of-failure. To address this concern, this article proposes a decentralized oracle which is based on a voting-based game that decides the truth or falsity of queries. In the context of this article, we are only interested in binary markets, i.e., queries which can be True, False, or Unknown. When requesting facts from an oracle, a user submits binary queries. Reporters (or certifiers) respond to the queries by placing monetary stake. A formal analysis of the system parameters is presented, which shows that the proposed platform incentivizes a Nash equilibrium for truthful reporting. An extension to the base protocol is also described and profiled against the original framework. Finally, we discuss a prototype architecture, along with additional features to be considered during implementation.

Gang Xue, Jia Xu, Hanwen Wu, Weifeng Lu · 5 authors

No abstract is available for this record.

Massimo Bartoletti

This paper explores the connection between software contracts and smart contracts. Despite the assonance, these two terms denote quite different concepts: software contracts are logical properties of software components, while smart contracts are programs executed on blockchains. What is the relation between them? We answer this question by discussing how to integrate software contracts in the design of programming languages for smart contracts.

Cobo Arróniz, Guillermo

With the evolving complexity of software systems, interest in software performance analysis has increasingly grown in recent years. Its main objective is to optimize software applications by analyzing its structure, behavior and dependencies, from design to code. Blockchain technologies, also known as distributed ledger technologies, have gained a lot of popularity in the recent years. Particularly the Ethereum blockchain, which apart from having its own cryptocurrency, is programmable. Meaning that developers can use it to create new decentralized applications which rely on smart contracts. Smart contracts are immutable computer programs that run deterministically in the context of the Ethereum Virtual Machine. The main purpose of this report is to explain the process of development of a tool to assist Ethereum developers to visually analyze static and dynamic behaviour of their smart contracts to improve their performance through optimizing gas usage.

David Minarsch, Seyed Ali Hosseini, Marco Favorito, Jonathan S. Ward

The user experience of interacting with distributed ledger technologies (DLT) is fraught with excessive complexity, high risk and unintuitive processes. Moreover, smart contracts deployed in these systems are restricted to being reactive. These limitations have negative implications on user adoption and prevent DLTs from being general purpose. We introduce a framework for the development of Autonomous Economic Agents (AEAs), software agents that act autonomously and pursue an economic goal, and demonstrate how AEAs complement existing decentralised ledgers as a second layer technology. In particular, the framework enables a simplified user experience through automation, supports modularisation and reuse of complex decision making and machine learning capabilities, and allows for proactive behaviour facilitating autonomy. We demonstrate these gains in the context of a specific use-case, a multi-agent trading system modelling a Walrasian Exchange Economy populated by a number of agents trading a basket of tokens.

Pinglan Liu, Wensheng Zhang

Smart contracts in the blockchain systems such as Ethereum are usually executed or verified by all nodes, and thus inefficient for heavy-duty computation. This paper addresses the limitation by proposing, implementing, and evaluating a practical and efficient solution based on a game theoretic approach. The solution defines a template of heavy-duty smart contract (HDSC); recruits only a small number of executors to execute heavy-duty tasks; employs a game theoretic scheme to enforce economically-rational executors to individually or collectively perform the execution correctly. Extensive game theoretic analysis has been conducted to show the security and computational efficiency of the solution even in face of collusion among the executors. As a proof of concept, the proposed solution has been implemented and experimented to demonstrate its practicality and compatibility with Ethereum.

James R. Riehl, Jonathan S. Ward

In this paper, we present a pricing mechanism that aligns incentives of agents who exchange resources on a decentralized ledger with the goal of maximizing transaction throughput. Subdividing a blockchain ledger into shards promises to greatly increase transaction throughput with minimal loss of security. However, the organization and type of the transactions also affects the ledger's efficiency, which is increased by wallet agents transacting in a single shard whenever possible while collectively distributing their transactions uniformly across the available shards. Since there is no central authority to enforce these properties, the only means of achieving them is to design the system such that it is in agents' interest to act in a way that benefits overall throughput. We show that our proposed pricing policy does exactly this by inducing a potential game for the agents, where the potential function relates directly to ledger throughput. Simulations demonstrate that this policy leads to near-optimal throughput under a variety of conditions.

Luís Pedro Arrojado da Horta, João Santos Reis, Mário Pereira, Simão Melo de Sousa

This paper introduces WhylSon, a deductive verification tool for smart contracts written in Michelson, which is the low-level language of the Tezos blockchain. WhylSon accepts a formally specified Michelson contract and automatically translates it to an equivalent program written in WhyML, the programming and specification language of the Why3 framework. Smart contract instructions are mapped into a corresponding WhyML shallow-embedding of the their axiomatic semantics, which we also developed in the context of this work. One major advantage of this approach is that it allows an out-of-the-box integration with the Why3 framework, namely its VCGen and the backend support for several automated theorem provers. We also discuss the use of WhylSon to automatically prove the correctness of diverse annotated smart contracts.

Juanjuan Li, Xiaochun Ni, Yong Yuan, Fei–Yue Wang

Bitcoin is gaining ground in recent years. In the Bitcoin system, miners provide computing power to confirm transactions in pursuit of transaction fees, while users compete by bidding transaction fees for faster confirmation. This process is in essence analogous to online ad auctions, where advertisers bid for more prominent ad slots. Therefore, inspired by ad auction research, we propose to apply the Generalized Second Price (GSP) auction mechanism in the dynamic confirmation game on Bitcoin transactions. Our model is targeted to deal with the problems caused by instability and low efficiency in the currently-adopted Generalized First Price (GFP) auction model in Bitcoin confirmation games. Besides, we use the “rank-by-cost” rule to replace the “rank-by-fee” rule, where each transaction’s cost is calculated by the user-submitted fee and the waiting time. Aiming to probe users’ equilibrium strategy, we first discuss the GSP game with complete information under synchronous submissions, and show that it has the Locally Envy-Free equilibrium. Then, we study the GSP game with incomplete information under asynchronous submissions, and define two types of strategies, i.e., the Farsighted Balanced (FB) strategy and the Instant Balanced (IB) strategy. The FB strategy is in line with users’ practical needs of determining fees so as to maximize the long-term payoffs; however it cannot generate a stable equilibrium. Alternatively, the IB strategy focuses on the instant payoff maximization, and if all users follow the IB strategy, their equilibrium fees can finally converge to a stable profile. Finally, we design computational experiments to validate our theoretical models and analysis. Our research findings indicate that this novel GSP mechanism is superior to the currently adopted GFP mechanism. Besides, the convergence of the GSP game under the IB strategy has also been illustrated by the computational experiments.

Richard Barnes

The tokenization of assets deployed to distributed ledger technology is increasingly cited to revolutionize financial services by allowing traditionally illiquid assets to be bought and sold on primary and secondary markets increasing asset liquidity, transparency and reducing transaction completion time. To realize these benefits it is important the token is transferrable, that is, portable from one distributed ledger to another. In this paper we survey current interoperability architectures and smart contract languages, identifying factors affecting the portability of tokenized assets. We propose a portability maturity model that can be used to help assess the current state of technology and supporting market infrastructure.

Nemitari Ajienka, Peter Vangorp, Andrea Capiluppi

Abstract A smart contract (SC) is a programme stored in the Ethereum blockchain by a contract‐creation transaction. SC developers deploy an instance of the SC and attempt to execute it in exchange for a fee, paid in Ethereum coins (Ether). If the computation needed for their execution turns out to be larger than the effort proposed by the developer (i.e., the gasLimit ), their client instantiation will not be completed successfully. In this paper, we examine SCs from 11 Ethereum blockchain‐oriented software projects hosted on GitHub.com , and we evaluate the resources needed for their deployment (i.e., the gasUsed ). For each of these contracts, we also extract a suite of object‐oriented metrics, to evaluate their structural characteristics. Our results show a statistically significant correlation between some of the object‐oriented (OO) metrics and the resources consumed on the Ethereum blockchain network when deploying SCs. This result has a direct impact on how Ethereum developers engage with a SC: evaluating its structural characteristics, they will be able to produce a better estimate of the resources needed to deploy it. Other results show specific source code metrics to be prioritised based on application domains when the projects are clustered based on common themes.

Clara Schneidewind, Ilya Grishchenko, Markus Scherer, Matteo Maffei

Ethereum has emerged as the most popular smart contract development platform, with hundreds of thousands of contracts stored on the blockchain and covering a variety of application scenarios, such as auctions, trading platforms, and so on. Given their financial nature, security vulnerabilities may lead to catastrophic consequences and, even worse, they can be hardly fixed as data stored on the blockchain, including the smart contract code itself, are immutable. An automated security analysis of these contracts is thus of utmost interest, but at the same time technically challenging for a variety of reasons, such as the specific transaction-oriented programming mechanisms, which feature a subtle semantics, and the fact that the blockchain data which the contract under analysis interacts with, including the code of callers and callees, are not statically known. In this work, we present eThor, the first sound and automated static analyzer for EVM bytecode, which is based on an abstraction of the EVM bytecode semantics based on Horn clauses. In particular, our static analysis supports reachability properties, which we show to be sufficient for capturing interesting security properties for smart contracts (e.g., single-entrancy) as well as contract-specific functional properties. Our analysis is proven sound against a complete semantics of EVM bytecode and an experimental large-scale evaluation on real-world contracts demonstrates that eThor is practical and outperforms the state-of-the-art static analyzers: specifically, eThor is the only one to provide soundness guarantees, terminates on 95% of a representative set of real-world contracts, and achieves an F-measure (which combines sensitivity and specificity) of 89%.

Clara Schneidewind, Ilya Grishchenko, M. Schérer, Matteo Maffei

Ethereum has emerged as the most popular smart contract development platform,\nwith hundreds of thousands of contracts stored on the blockchain and covering a\nvariety of application scenarios, such as auctions, trading platforms, and so\non. Given their financial nature, security vulnerabilities may lead to\ncatastrophic consequences and, even worse, they can be hardly fixed as data\nstored on the blockchain, including the smart contract code itself, are\nimmutable. An automated security analysis of these contracts is thus of utmost\ninterest, but at the same time technically challenging for a variety of\nreasons, such as the specific transaction-oriented programming mechanisms,\nwhich feature a subtle semantics, and the fact that the blockchain data which\nthe contract under analysis interacts with, including the code of callers and\ncallees, are not statically known.\n In this work, we present eThor, the first sound and automated static analyzer\nfor EVM bytecode, which is based on an abstraction of the EVM bytecode\nsemantics based on Horn clauses. In particular, our static analysis supports\nreachability properties, which we show to be sufficient for capturing\ninteresting security properties for smart contracts (e.g., single-entrancy) as\nwell as contract-specific functional properties. Our analysis is proven sound\nagainst a complete semantics of EVM bytecode and an experimental large-scale\nevaluation on real-world contracts demonstrates that eThor is practical and\noutperforms the state-of-the-art static analyzers: specifically, eThor is the\nonly one to provide soundness guarantees, terminates on 95% of a representative\nset of real-world contracts, and achieves an F-measure (which combines\nsensitivity and specificity) of 89%.\n

Xiaochi Zhou, Mei Qi Lim, Markus Kraft

No abstract is available for this record.

Cong T. Nguyen, Diep N. Nguyen, Hoang Thai Dinh, Hoang-Anh Pham · 7 authors

Mobile service providers (MSPs) are particularly vulnerable to roaming frauds, especially ones that exploit the long delay in the data exchange process of the contemporary roaming management systems, causing multi-billion dollars loss each year. In this paper, we introduce BlockRoam, a novel blockchain-based roaming management system that provides an efficient data exchange platform among MSPs and mobile subscribers. Utilizing the Proof-of-Stake (PoS) consensus mechanism and smart contracts, BlockRoam can significantly shorten the information exchanging delay, thereby addressing the roaming fraud problems. Through intensive analysis, we show that the security and performance of such PoS-based blockchain network can be further enhanced by incentivizing more users (e.g., subscribers) to participate in the network. Moreover, users in such networks often join stake pools (e.g., formed by MSPs) to increase their profits. Therefore, we develop an economic model based on Stackelberg game to jointly maximize the profits of the network users and the stake pool, thereby encouraging user participation. We also propose an effective method to guarantee the uniqueness of this game's equilibrium. The performance evaluations show that the proposed economic model helps the MSPs to earn additional profits, attracts more investment to the blockchain network, and enhances the network's security and performance.

Maximilian Wöhrer, Uwe Zdun

Due to the conceptual discrepancy between legal contract terms and code, understanding and creating smart contracts without errors can be difficult. This article proposes smart contract design patterns and their automated application through (the use of) a domain-specific language and code generation.