Fine-Grained Remote Signcryption approach to cloud storage systems

Secure cloud storage requires confidentiality to prevent data leakage, access control to manage user permissions, and integrity verification to detect tampering. Attribute-Based Signcryption (ABSC) provides confidentiality and access control; however, integrity verification requires downloading the entire signcrypted dataset. This incurs excessive communication overhead, especially when data is corrupted, as users retrieve malicious and unusable content. Conversely, remote data integrity checking schemes support remote inspection but lack confidentiality and access control. This paper proposes Fine-Grained Remote Signcryption (FGRS), a novel and unified framework that integrates confidentiality, access control, and remote integrity verification into a single primitive. Unlike hybrid approaches, FGRS eliminates redundant operations and enables lightweight integrity verification through a challenge-response protocol that exchanges only a few kilobytes of data without accessing the data. Under attribute-intensive access policies, FGRS provides a trade-off between computation, communication, and input/output overheads by allowing authorized users to remotely verify data integrity and download the verified data for decryption. FGRS achieves IND-CCA security and unforgeability under the bilinear Diffie–Hellman assumption. Experimental results show that for 4MB data with 200 attributes, FGRS signcrypts faster and reduces verification overhead by 1 0 4 × compared to the ABSC schemes. It also decreases designcryption cost by 10 × over some ABSC approaches.