Enabling Secure Auditing and Deduplication in Multi-replica Cloud Storage

Multi-replica storage is an advanced extension of traditional cloud storage that allows data owners to customize the number of backups for file blocks based on their relative importance. In such settings, remote auditing mechanisms are essential for verifying data integrity and ensuring that the cloud service provider (CSP) maintains the pre-negotiated number of replicas. However, existing schemes often expose block positions and backup quantities to the CSP, making users' data vulnerable to template attacks. Meanwhile, secure deduplication significantly reduces storage overhead and user costs while preserving data confidentiality. In this paper, we propose a novel multi-replica cloud storage scheme that, for the first time, simultaneously supports cross-user deduplication and integrity auditing in the ciphertext domain. The proposed scheme can not only protect data privacy from template attacks but also enable the elimination of redundant ciphertext replicas and audit authentication tags across users at the block level. Formal analysis validates the correctness and security guarantees of our scheme. Experimental results demonstrate its effectiveness with modest overhead.