A data destruction model based on lifecycle control under cloud storage environment was proposed to solve the lack of effective data destruction mechanism for user data, and that data security was threatened and destruction time was controlled in the life cycle, which greatly limited the development of cloud services. The plain text was processed by functional transformation to generate the cipher text and metadata and avoid the complex key management. Secondly, in order to improve the controllability of data destruction, a self-destruction data objects based on controllable time was designed, which made any illegal access of expired objects to trigger the assured deletion by rewriting program, and realized the data destruction based on lifecycle control. The analysis and experimental results show that the scheme can enhance the flexibility and controllability of data destruction and reduce the performance cost, while protecting the data safely and effectively.

Focusing on the issue that current fully homomorphic encryption schemes are not practical, Gentry-Sahai-Waters (GSW) homomorphic encryption scheme was improved and a leveled fully homomorphic encryption scheme based on Ring Learning with Error (Ring-LWE) and GSW was proposed. Firstly, a basic public key encryption scheme was constructed on Ring-LWE problem, the approximate eigenvector method was used to make it have homomorphic addition and multiplication properties, and the randomized function technique was introduced to simplify the analysis of noise blow-up. Secondly, the correctness and security of the proposed scheme was proved, the correctness of homomorphic addition, multiplication and NAND operation was analyzed in detail. Finally, security parameter was set in accordance with the noise blow-up with homomorphic evaluation and the security of Ring-LWE problem, fast Fourier transformation was adopted to reduce the computational complexity of polynomial multiplication, then a leveled fully homomorphic encryption scheme was given. The size of the pubic key in new scheme is shorter than that in GSW and the computational complexity of NAND gate is reduced from Õ(( nL) ^2.37) to Õ( nL ²).