Efficient dynamic multi-replica auditing for the cloud with geographic location

Abstract Data backup is a pervasive strategy adopted by cloud service providers (CSPs) to avoid potential risks of data loss. As a result, a CSP normally maintains multiple replicas for each piece of data on geographically distributed servers to improve reliability. A key problem of this replication technique is that users will be charged more when more replicas are stored. Therefore, an auditing service is desired to help users verify whether an untrusted CSP stores all their replicas in different geographic locations or not. In this paper, we propose a dynamic multi-replica auditing scheme that has the following features: (1) it can verify both the integrity and geographic locations of a cloud user’s data replicas; (2) the proposed scheme can identify different copies with geographic locations, which reduces the complexity in data preprocessing, dynamic operations and backup recovery; (3) by introducing an Indexed Merkle Hash Tree (IMHT), we can reduce overall costs of existing Merkle Hash Trees. We prove the security of the proposed scheme under the random oracle model, and further provide a comprehensive comparison between the proposed scheme and existing schemes. The theoretical analysis and experiment evaluation show that our scheme reduces both the communication and computation costs compared with existing schemes. The analysis also shows that the proposed scheme can achieve 99% verification probability by challenging only 90 data blocks.