Secure long-term off-chain storage in the NFTs era

“What is the meaning of creating an unforgeable token on a highly secured network if somebody can alter, relink or destroy your possession? As long as the value of your artwork is reliable on a central service you do not own anything.”

There has been an increasing interest in Blockchain systems since Bitcoin was launched in 2009. Many different platforms have been proposed, such as Ethereum and Hyperledger. Cryptocurrencies are the most common use of blockchain systems today. However, a large number of other applications have emerged. A group of applications that have become extremely popular since 2020 involve the use of non-fungible tokens (NFTs) [1].

In general, NFTs represent digital assets [2]. Each NFT is unique and thus not mutually interchangeable with another NFT in terms of value, in contrast with fungible tokens (e.g. all €1 coins have the exact same value, all bitcoins are equal, etc). Recent applications use NFTs as proof of ownership for digital art, photos, collectible items, audio [3] and video files, game assets, among others. 

NFTs are commonly implemented using smart contracts, which makes Ethereum the most common platform for NFT-based applications. Depending on the application, storing data associated with a NFT in the blockchain may be too expensive. For instance, a picture may be too big to be stored on-chain. In order to circumvent this limitation, it is common to employ off-chain storage solutions for the NFT data, and store on-chain only some kind of reference to the data (e.g. an URL) [4].

Many decentralized solutions for off-chain storage have been proposed [5]. One of the most common is IPFS [6]. However, the emergence of the NFT economy is revealing many open issues regarding off-chain storage. Some NFT marketplaces, for example, employ centralized solutions for storing NFT off-chain data. In a recent case [7], an artist was able to modify the NFT images of an already sold collection, without any permission from the actual owner, in the largest NFT marketplace today [8]. Even when decentralized off-chain storage solutions are employed, there is no guarantee about the availability of data after a long period of time, this market is still very young thus there are no studies regarding long-term storage. Other open issues include access control, confidentiality, traceability [9], and GDPR compliance [10].


This topic is wide in scope and may result in multiple master theses. As a first step the student will have to narrow down the scope of the thesis to focus on just one or two of the following research questions:

  • How current off-chain solutions fare regarding long-term storage?
  • How immutable is the data in current marketplaces and/or storage solutions?
  • Do nodes keep storing data that is not popular?
  • What are the requirements for a NFT ecosystem? 
  • Do requirements change depending on specific use cases (digital art, games, music, etc)?
  • How to incentivize long-term storage of off-chain data?
  • How to evaluate long-term availability?
  • How to ensure off-chain data is not improperly modified or deleted?
  • Is it possible to update off-chain data?
  • Is it possible to delete off-chain data (right to be forgotten)?
  • Is it possible to enforce some kind of decentralized access control for reading/writing the NFT off-chain data?
  • How to remove the trust requirements between creator, buyer, seller and the centralized NFT marketplaces?
  • Is it possible to keep track of modifications made to off-chain data?

Expected tasks

  • Understand what an NFT is, and the many aspects related to its implementation (standards, smart contracts, dApps, external database, etc)
  • Understand the trade-offs between on-chain and off-chain storage
  • Understand current off-chain storage solutions for NFTs and identity their shortcomings
  • Understand how current marketplaces work from the point of view of storage
  • Define metrics for evaluating solutions
  • Design new architectures, mechanisms, and/or protocols for securing NFTs off-chain storage and/or the trading process
  • Read, understand, and modify existing code from open source projects
  • Comparative evaluation: program, simulate and demonstrate the improvements of the proposed mechanisms according to the defined metrics


  • Basic understanding of distributed systems principles
  • Programming skills
  • Capability of understanding and modifying existing code (open source projects)
  • Experience with deploying software on multiple nodes
  • Experience with network and/or event-based simulators is a plus


If you are interested, please send an e-mail to and in order to schedule a meeting.


[1] NFT sales top $2 billion in first quarter, with twice as many buyers as sellers,

[2] Q. Wang et al., “Non-Fungible Token (NFT): Overview, Evaluation, Opportunities and Challenges,” 2021,

[3] Kings of Leon Will Be the First Band to Release an Album as an NFT,

[4] NFT School,

[5] Daniel et al., “IPFS and Friends: A Qualitative Comparison of Next Generation Peer-to-Peer Data Networks,” 2021,

[6] IPFS,

[7] OpenSea collector 'pulls the rug' on NFTs to highlight arbitrary value,

[8] OpenSea,

[9] Bal et al., “NFTracer: A Non-Fungible Token Tracking Proof-of-Concept Using Hyperledger Fabric,” 2019,

[10] Casino et al., “Immutability and Decentralized Storage: An Analysis of Emerging Threats,” IEEE Access, 2019,


Emneord: blockchain, distributed ledger, distributed systems, storage
Publisert 8. sep. 2021 14:16 - Sist endret 8. sep. 2021 15:27

Omfang (studiepoeng)