Genuine On-Chain and Off-Chain Collaboration: Achieving Secure and Non-Repudiable File Sharing in Blockchain Applications

Blockchain’s immutable and traceable records and independence from third-party involvement make it an irreplaceable tool in applications involving multiple stakeholders. However, securely sharing off-chain files among stakeholders while ensuring non-repudiation is a significant challenge. This is because blockchain cannot monitor off-chain behavior, and stakeholders may refuse to acknowledge records on the chain. In this study, we propose an efficient solution for secure file sharing among stakeholders through on-chain and off-chain collaboration for blockchain applications with additional off-chain storage modules. Specifically, we design an adapted blockchain structure and propose a consensus process integrated with the sharing process to manage off-chain behavior and prevent delivery repudiation. We also incorporate a ciphertext policy into the sharing process to ensure the integrity and confidentiality of the shared file. Additionally, we propose a watermarking protocol in conjunction with blockchain records to hold unauthorized disclosure behavior accountable. Our scheme extends the management scope of blockchain to off-chain and achieves 32x, 19x, and 1.48x higher throughput than Bitcoin, Ethereum, and Fabric, respectively.