中文摘要：

全同态加密技术是解决云环境隐私安全问题的有效方法。考虑云环境下用户多样性特征,提出基于策略的多用户全同态加密方案（PB-MUFHE）,该方案在全同态加密算法的基础上,通过在密文中设定适当的访问策略以及在密钥中设定属性,从而满足多用户密文的全同态运算以及多用户共享,并支持细粒度的访问控制。安全分析证明PB-MUFHE可以抵制共谋攻击,且在LWE困难度假设随机域模型下是IND-CPA安全的。性能评估表明：PB-MUFHE高效地实现密文数据的全同态运算,并能有效地支持访问控制和多用户共享。

英文摘要：

The full homomorphic encryption technology is an effectively way to solve the problem of cloud computing privacy and security. Considering user diversity in cloud environment, a policy based multi-user full homomorphic encryption scheme （PB-MUFHE） is proposed. On the basis of full homomorphic encryption algorithm, the scheme sets appropriate access policy in the encrypted data and sets the attribute in the key, which is not only to meet full homomorphic operation of the multi-user ciphertext and the multi-user share, but also to support for fine-grained access control Se- curity analysis shows that PB-MUFHE can resist collusion attacks, and is proved IND-CPA security in the random fields model under the LWE harder assumption. Performance assessment demonstrates that PB-MUFHE ciphertext can efficiently implement data fully homomorphy operation and effectively support access control and multi-user shared.