Public integrity auditing for dynamic group cooperation files with efficient user revocation

• Our PAGCF provides the public integrity auditing service of group cooperation files with dynamics. That is, any group user can upload the group cooperation file to the cloud server, where the file can be modified, inserted and deleted by any cooperative group user. • To detect malicious operations or obtain the workload of group users, any group user in PAGCF can keep track of the identity of signer and the time of all operations according to the state information of the file and certificate database. However, out-of-group users cannot trace the identity of signer due to anonymity, which realizes the identity privacy for group users. • PAGCF not only can realize effective revocation so that revoked users lose privileges of updating the group cooperation file and tracing the identity of the signers, but also prevents the collusion attack of revoked users and other adversaries. Besides, group users are stateless because they do not need to maintain a list locally, which significantly reduce the storage cost for group users. • The security analyses show that PAGCF can verify the integrity of group cooperation files and ensure their content privacy during the public audit process. The performance analyses demonstrate that PAGCF is efficient. With the rise of online cloud files, more and more online files are generated by group cooperation in recent years. However, there exist many security problems to be solved urgently for online cooperation files, such as how to verify the integrity of group cooperation files and realize its dynamic update and how to further trace the identity of signer (i.e., operator) who upload or update the group cooperation files. To address the above problems, we propose a secure public integrity auditing scheme for group cooperation files in this paper, named PAGCF. First, PAGCF not only can verify the integrity of group cooperation files, but also supports the dynamic update of group cooperation files via the skip list. Second, any legitimate user can trace the identity of signer to resist malicious tampering and workload disputes of group users. Additionally, PAGCF also achieves user stateless without requiring users to maintain a list locally. Third, PAGCF not only can realize effective group user revocation so that revoked users lose privileges to update the group cooperation file and trace the identity of signer, but also can resist the collusion attack of malicious adversaries and revoked users. Finally, numeric analyses and experiment results demonstrate the efficiency of our proposed scheme.