Dipartimento di Ingegneria informatica, automatica e gestionale

The concept of Non-Fungible Token (NFT) has found many applications with great impact. One of the most appealing uses of NFTs is the possibility of creating and managing an NFT collection where each token regulates the ownership of a digital asset and new tokens can be minted according to some rules. In this work, we investigate the natural question of whether a digital asset could be duplicated inside a collection of NFTs. Interestingly, while intuitively uniqueness should be enforced by the use of NFTs, we observe that the existence of clones is possible according to the mainstream approaches of Ethereum (i.e., ERC-721 contracts) and Algorand (i.e., ASAs). Moreover, we have scrutinized famous NFT collections that have been built on such decentralized platforms and our findings show that, unfortunately, the uniqueness of a digital asset in a collection (e.g., the guarantee that at most one NFT is generated for the ownership of a specific digital painting) is at risk if the minter (i.e., a single point of failure) is at some point corrupted. Next, we propose a natural and simple functionality FCollNFT abstracting the management of NFT collections that, by design, does not allow clones in a collection. While in general, ERC-721 and ASAs do not securely realize FCollNFT, we discuss the design of an NFT collection that is compliant with the ERC-721 standard and at the same time realizes FCollNFT, therefore, guaranteeing by design that even a malicious minter can not introduce clones in the collection.