BDACD: Blockchain-based decentralized auditing supporting ciphertext deduplication

Public auditing enables data owners to entrust a third-party auditor (TPA) to perform auditing tasks periodically. To resist malicious TPAs, a plethora of blockchain-based public auditing mechanisms have been proposed. However, existing schemes cannot effectively mitigate single point of failure and collusion between TPAs and miners. These schemes are burdened by significant wastage of storage resources due to the presence of redundant data. In this paper, we propose a blockchain-based decentralized auditing scheme supporting ciphertext deduplication (BDACD). BDACD leverages a decentralized blockchain, which takes over the role traditionally played by a centralized TPA. A decentralized autonomous organization is incorporated to enhance resistance against collusion attacks. By integrating advanced ciphertext deduplication techniques, BDACD effectively mitigates storage overhead. Furthermore, we introduce a novel concept, T-Merkle hash tree, along with a corresponding search algorithm. This innovation significantly enhances blockchain storage utilization and enables efficient half-interval searches within a block. To ensure accountability and fairness, a smart contract is employed to establish an arbitration mechanism. This mechanism serves a dual purpose: penalizing any malevolent actions by cloud servers and providing adequate compensation to data owners whose data integrity has been compromised. Detailed security analysis and performance evaluation demonstrate BDACD has desirable security and efficiency.