Protecting Non Fungible Mutable Tokens: an Application in the Metaverse

Non-Fungible Tokens (NFTs) are currently used in a large number of scenarios, from digital art to the metaverse, to trace the ownership of assets exchanged between users. However, most NFT defining standards, such as the widely adopted ERC 721 for the Ethereum protocol, have been designed with immutable assets only in mind. As such, they are not suitable for representing assets with features that may need to be updated during their lifetime. To overcome this issue, in the literature have been proposed new models that properly represent and protect mutable assets through NFTs, such as Non Fungible Mutable Tokens, NMTs. In this paper, we expanded the NMT model with a security support meant to protect assets’ features updates through access control policies that are defined by the asset creator and the current asset owner and enforced during the assets’ lifetime. Policing updates is of paramount importance, because it protects the asset from unintended updates that could greatly alter the asset itself and its value. The main contributions of this paper are a detailed description of the NMT smart contracts architecture and internal dependencies, as well as an experimental validation of NMTs by providing the implementation of a NMT representing a wearable (a jacket) in Decentraland, a popular metaverse environment.