Concerning the data's confidentiality when stored in public cloud storage system and the system's performance, a secure and efficient scheme was proposed and applied in the cloud storage system of cryptography with cryptographic fine-grained access control, which was based on Ciphertext-Policy Attribute-Based Encryption (CP-ABE). In the proposed scheme, the original data were firstly divided into a number of slices by the ( k,n)algorithm. Then some of slices were randomly chosen to encrypt. At last, the encrypted slices were published to the cloud storage, and only one copy of these slices was stored. The proposed scheme was proved that it could improve the performance of the user's cancel operation and reduce the cost of the storage space. At the same time, the system was also proved to be safe on calculation by the analysis of the security. By contrast, the experimental results show that, the data management time for the data owner is decreased obviously through optimizing the user revocation phase. The data storage cost is also decreased because of only storing one copy of data. The proposed scheme achieves secure sharing and efficient storage of the sensitive data in the public cloud storage.

The existing Provable Data Possession (PDP) schemes cannot be directly applied in mobile cloud computing because the terminal' storage space and computing power are limited for the computationally intensive operations in those schemes. Addressing this issue, an Agent-based PDP scheme was proposed for mobile cloud computing. A semi-trusted security computation Agent was introduced between the terminal and the cloud server in order to help end-users complete the computationally intensive operations, so that the PDP scheme can be applied in mobile computing. A concrete PDP scheme was presented and a formal proof shows it satisfies the Chosen Plaintext Attack (CPA) security under random oracle model. The quantitative analysis results show that the scheme is fit for mobile cloud computing.