A Blockchain-Based Revocable and Fine-Grained Access Control Scheme Against EDoS Attacks

Today, the completion of a project often necessitates close collaboration among multiple organizations. How to securely and reliably achieve file sharing for users across different organizations has become a prominent research focus. Fine-grained access control over cloud-stored data is enabled for file owners through the use of ciphertext-policy attribute-based encryption (CP-ABE). However, insufficient trust between organizations, complex ciphertext updates, and the lack of auditable access history present significant challenges to data sharing. Moreover, cloud servers are vulnerable to economic denial of sustainability (EDoS) attacks, which are executed by malicious users generating a flood of download requests. Against this backdrop, we devise an enhanced ciphertext-policy attribute-based encryption scheme leveraging blockchain to tackle the aforementioned vulnerabilities. Specifically, the scheme introduces chameleon hashes and blockchain to ensure unique and traceable user identities. In addition, to resist EDoS attacks, challenge ciphertext is generated and stored on the blockchain to verify user download permissions. Only verified users can download ciphertext from the cloud sever. In addition, our scheme supports ciphertext updates without modifying the original project files. Performance analysis shows that our proposal can track access activity and resist EDoS attacks while protecting file confidentiality. Experimental results indicate that the encryption time and attribute revocation time are reduced by at least 66.7% and 59.8% respectively, and the total time cost is reduced by at least 39.03% compared to related schemes. The lower time and storage costs make our solution more practical for cross-organizational file sharing.