Identity-preserving public auditing for shared cloud data

Cloud storage enables users to remotely store their data and share the data through the cloud. Existing integrity auditing schemes for shared data are often not identity-preserving and have high auditing cost, and hence are still far from practical application. In this work, we propose a public auditing scheme for shared data in cloud storage with identity privacy preservation. To preserve identity privacy against the auditor, we convert signatures computed by different users into signatures computed by the challenge user with proxy re-signature. Our scheme supports user revocation without re-signing signatures computed by revoked users, while the integrity of shared data can still be correctly checked. Furthermore, the auditing is efficient in the sense that the number of pairing operations during auditing is independent of the number of challenged blocks and users. We further present a batch auditing supporting multiple auditing delegations from different groups instead of only the same group. Security analysis demonstrates that our scheme is provably secure. Numeric analysis and simulation results show that both computation and communication costs of our scheme are lower than in existing schemes.