Cloud audit scheme is a mechanism for verifying the integrity of user data stored on cloud servers. Existing audit schemes often require data owner (DO) to generate tags, which will be used in the later audit phase, on the data files to be stored itself. However, this mode still has the following issues: (1) The calculation and generation process of tags imposes a significant computational burden on DO; (2) Frequent use of private key for tag generation exposes it to increased security risks. To address these issues, this paper proposes an assistant-based tag collaborative generation process. Specifically, we introduce an assistant that holds a key derived from the DO’s private key and performs the bulk of the tag computation. In this way, the DO only needs to carry out a few lightweight operations to complete the final authentication tag. Moreover, the DO can revoke or update the assistant at any time without changing the original public/secret key pair. In addition, in order to achieve privacy protection against auditor during the audit process, this paper also proposes a transparent audit based on Blockchain. Finally, the security analysis indicates that our scheme achieves the required security in terms of cloud audit reliability, tag collaborative computing security, and privacy protection. The performance analysis also shows that it has certain advantages compared to similar schemes, especially in saving DO’s computation costs.

A cloud audit scheme is a security mechanism that helps cloud users detect whether their data stored on cloud servers is integral. The issue of key exposure is a serious security threat to cloud audit scheme. The reason lies in that once the user’s authentication key is exposed, most existing audit schemes will become insecure. Meanwhile, existing implementation schemes often introduce third-party auditor (TPA) to assist users in performing audit tasks, and even to update user’s key against key-exposure attacks. However, it is well-known that TPA’s core function is to perform audit tasks and it is not entirely trustworthy. The key update operation based on TPA is not realistic in practical applications. In this article, we propose an identity-based cloud auditing scheme, which resists key-exposure attack by regularly issuing new secret keys to users by the key generation center. The identity-based property guarantees that user’s public identity is unchanged. Moreover, in order to prevent TPA from obtaining users’ stored data content through the audit process, an audit mechanism based on the smart contracts of Blockchain will also be given. In addition, introducing a “two-dimensional” partitioning mechanism on data file can greatly reduce the burden of tag generation. Finally, security and performance analyses will be conducted on the proposed scheme. The results show that our scheme has good properties in terms of key-exposure resilience and privacy-protection on stored data, and also has good performance advantages in the implementation process.

In recent years, the medical industry is generating a large amount of data. How to securely store and reliably share these medical data has been a hot research topic. Cloud storage technology can be applied to the medical industry to adapt to the rapid growth of medical data. However, cloud-based data storage and sharing systems face a series of security issues: whether the integrity of outsourced medical data can be guaranteed, and malicious access between different medical institutions may leak user's privacy. This article proposes a system that simultaneously solves the integrity auditing of medical data and securely data sharing between different medical institutions under the terminal-edge-cloud framework. Specifically, patients/doctors are treated as terminal users, medical institutions are viewed as edge nodes, and medical clouds form the central storage layer. In the process of data auditing, third-party auditor can achieve integrity auditing of medical cloud storage data. Moreover, different medical institutions use private-set-intersection technology to share the common user's electronic medical data, while for other users not in intersection set, their data does not need to be shared. Finally, security and performance analyses show that our proposed system is provable secure and has high computational and communication efficiency.