SecArchive: Provable Data Possession for Archival Storage Deterring Subcontracting Attacks in Multi-Cloud Multi-Copy

Multi-cloud, multi-copy architectures enhance disaster recovery capability of cloud storage. Provable Data Possession (PDP) provides integrity verification for cloud data. Archival storage—characterized by large data volumes and redundant backups—demands efficient and secure solutions. However, most existing solutions for archival storage overlook critical threats, particularly subcontracting attacks, wherein cloud storage servers (CSs) unlawfully delegate storage responsibilities to a third party. To this end, we make the following efforts: 1) Deterrence against Subcontracting Attacks. The CS is deterred from subcontracting storage tasks, as doing so would expose its private key to the third party; 2) Low Tag Complexity. The Data Owner (DO) generates only one set of tags for the source file ($n$blocks). Adding each copy requires merely one additional elliptic curve point multiplication during the tag generation. Consequently, the computational complexity of tag generation for$d$copies is$O(n+d)$, which drastically outperforms the$O(nd)$of prior schemes; 3) Optimized Auditing. Auditors can efficiently challenge distinct blocks across different copies within a single query, eliminating redundant checks; and 4) Secure and Efficient. Rigorous security proofs and efficiency analyses confirm the protocol’s suitability for secure, practical multi-cloud archival storage.