：云服务中现有访问控制方案对可信第三方具有强烈依赖性。针对该问题，提出一个基于属性的分布式云访问控制方案。建立云访

问控制模型，采用ABE的加密树方式构造访问控制策略，并给出用户撤销及策略更新方法。安全性分析表明，该方案能够抵抗共谋攻击，

具有数据保密性以及后向前向保密性。-Now existing access control scheme has the strong dependence to trusty third party in cloud．With regard to this problem，this paper

proposes all access control scheme based on attribute．It designs an access control model in cloud，constructs all access control policy which adopts

the way of Attribute—based Encryption(ABE)tree，and presents a method of user revocation and policy updates．Security analysis indicates that the

scheme has the features ofcollusion—resistance，data confidentiality and backward and forward secrecy．