Implementing Smart Contracts: The case of NFT-rental with “pay-per-like”

Non-fungible tokens(NFTs) can represent artworks exhibited for marketing purposes on webpages of companies or online stores - analogously to physical artworks. Lending of NFTs is an attractive form of passive income for owners but comes with risks (e.g., items are not returned) and costs for escrow agents. Similarly, renters have difficulties in anticipating the impact of artworks, e.g., how spectators of NFTs perceive them. To address these challenges, we introduce an NFT rental solution based on a pay-per-like pricing model using blockchain technology, i.e., smart contracts based on the Ethereum chain. We find that blockchain solutions enjoy many advantages also reported for other applications, but interestingly, we also observe dark sides of (large) blockchain fees. Blockchain solutions appear unfair to niche artists and potentially hamper cultural diversity. A trust-cost tradeoff arises to handle fraud caused by parties outside the blockchain. Code for the solution is available on GitHub at BLINDEDforREVIE

Implementing Smart Contracts: The case of NFT-rental with pay-per-like

Non-fungible tokens(NFTs) are on the rise. They can represent artworks exhibited for marketing purposes on webpages of companies or online stores -- analogously to physical artworks. Lending of NFTs is an attractive form of passive income for owners but comes with risks (e.g., items are not returned) and costs for escrow agents. Similarly, renters have difficulties in anticipating the impact of artworks, e.g., how spectators of NFTs perceive them. To address these challenges, we introduce an NFT rental solution based on a pay-per-like pricing model using blockchain technology, i.e., smart contracts based on the Ethereum chain. We find that blockchain solutions enjoy many advantages also reported for other applications, but interestingly, we also observe dark sides of (large) blockchain fees. Blockchain solutions appear unfair to niche artists and potentially hamper cultural diversity. Furthermore, a trust-cost tradeoff arises to handle fraud caused by manipulation from parties outside the blockchain. All code for the solution is publicly available at: https://github.com/asopi/rental-projectComment: Preprint of accepted paper of the 18th International Conference on Wirtschaftsinformatik, 202

Trustless communication across distributed ledgers: impossibility and practical solutions

Since the advent of Bitcoin as the first decentralized digital currency in 2008, a plethora of distributed ledgers has been created, differing in design and purpose. Considering the heterogeneous nature of these systems, it is safe to say there shall not be ``one coin to rule them all". However, despite the growing and thriving ecosystem, blockchains continue to operate almost exclusively in complete isolation from one another: by design, blockchain protocols provide no means by which to communicate or exchange data with external systems. To this date, centralized providers hence remain the preferred route to exchange assets and information across blockchains~-- undermining the very nature of decentralized currencies. The contribution of this thesis is threefold. First, we critically evaluate the (im)possibilty, requirements, and challenges of cross-chain communication by contributing the first systematization of this field. We formalize the problem of Cross-Chain Communication (CCC) and show it is impossible without a trusted third party by relating CCC to the Fair Exchange problem. With this impossibility result in mind, we develop a framework to design new and evaluate existing CCC protocols, focusing on the inherent trust assumptions thereof, and derive a classification covering the field of cross-chain communication to date. We then present XCLAIM, the first generic framework for transferring assets and information across permissionless distributed ledgers without relying on a centralized third party. XCLAIM leverages so-called cryptocurrency-backed assets, blockchain-based assets one-to-one backed by other cryptocurrencies, such as Bitcoin-backed tokens on Ethereum. Through the secure issuance, transfer, and redemption of these assets, users can perform cross-chain exchanges in a financially trustless and non-interactive manner, overcoming the limitations of existing solutions. To ensure the security of user funds, XCLAIM relies on collateralization of intermediaries and a proof-or-punishment approach, enforced via smart contracts equipped with cross-chain light clients, so-called chain relays. XCLAIM has been adopted in practice, among others by the Polkadot blockchain, as a bridge to Bitcoin and other cryptocurrencies. Finally, we contribute to advancing the state of the art in cross-chain light clients. We develop TxChain, a novel mechanism to significantly reduce storage and bandwidth costs of modern blockchain light clients using contingent transaction aggregation, and apply our scheme to Bitcoin and Ethereum individually, as well as in the cross-chain setting.Open Acces

PDFS: Practical Data Feed Service for Smart Contracts

Smart contracts are a new paradigm that emerged with the rise of the blockchain technology. They allow untrusting parties to arrange agreements. These agreements are encoded as a programming language code and deployed on a blockchain platform, where all participants execute them and maintain their state. Smart contracts are promising since they are automated and decentralized, thus limiting the involvement of third trusted parties, and can contain monetary transfers. Due to these features, many people believe that smart contracts will revolutionize the way we think of distributed applications, information sharing, financial services, and infrastructures. To release the potential of smart contracts, it is necessary to connect the contracts with the outside world, such that they can understand and use information from other infrastructures. For instance, smart contracts would greatly benefit when they have access to web content. However, there are many challenges associated with realizing such a system, and despite the existence of many proposals, no solution is secure, provides easily-parsable data, introduces small overheads, and is easy to deploy. In this paper we propose PDFS, a practical system for data feeds that combines the advantages of the previous schemes and introduces new functionalities. PDFS extends content providers by including new features for data transparency and consistency validations. This combination provides multiple benefits like content which is easy to parse and efficient authenticity verification without breaking natural trust chains. PDFS keeps content providers auditable, mitigates their malicious activities (like data modification or censorship), and allows them to create a new business model. We show how PDFS is integrated with existing web services, report on a PDFS implementation and present results from conducted case studies and experiments.Comment: Blockchain; Smart Contracts; Data Authentication; Ethereu