Cloud storage is popular to users for its high scalability, high reliability, and low-cost data management. However, it is an important security problem to safeguard the cloud data integrity. Currently, providing public auditing services based on semi-trusted third party is the most popular and effective cloud data integrity audit scheme, but there are still some shortcomings such as single point of failure, computing power bottlenecks, and low efficient positioning of erroneous data. Aiming at these defects, a dynamic cloud data audit model based on block chain was proposed. Firstly, distributed network and consensus algorithm were used to establish a block chain audit network with multiple audit entities to solve the problems of single point of failure and computing power bottlenecks. Then, on the guarantee of the reliability of block chain, chameleon Hash algorithm and nest Merkle Hash Tree (MHT) structure were introduced to realize the dynamic operation of cloud data tags in block chain. Finally, by using nest MHT structure and auxiliary path information, the efficiency of erroneous data positioning was increased when error occurring in audit procedure. The experimental results show that compared with the semi-trusted third-party cloud data dynamic audit scheme, the proposed model significantly improves the audit efficiency, reduces the data dynamic operation time cost and increases the erroneous data positioning efficiency.

The data is usually shared by a group of users in cloud computing. The third party auditor can obtain the the identities of group members through their signatures of data blocks. In order to protect the identities of group members, the existing public audit schemes for shared data all hide the identities of group members. However, the anonymity of identity leads to the problem that a member of the group can change the shared data maliciously without being found, and the amount of computation is large for resource constrained devices in the process of generating signature for users. The existing public audit schemes have the problems that the identity of data block can not be traced and the amount of calculation of generating shared data block signature is large. In order to solve the above problems, A Scheme of sharing cloud Data Audit supporting user traceability and lightweight (ASDA) was proposed. Firstly, the security mediator was used to replace the user signature to protect the identities of group members. The information of user was saved while signing and it could be traced back that the data block was modified by which member through the above information, which could ensure the traceability of the identity of data block. Then, a new data block blinding technology was used to reduce the amount of client computing. The experimental results show that, compared with Storing shared Data on the cloud Via Security-mediator (SDVS) scheme, the proposed scheme reduces the computing time of users and realizes the traceability of shared data blocks.