Cloud storage has been widely used since its birth because of its convenience and low price.But compared with the traditional system,the users in the cloud storage system lost the direct control of the data,so users are most concerned about whether the data stored in the cloud are security,where integrity is one of the security needs.Public au-dit is an effective way to verify the integrity of cloud data.Existing research work can not only achieve cloud data integ-rity verification,but also support dynamic data update audit.However,such schemes also suffer from some drawbacks, for example,when multiple second-level file block update tasks are implemented,users need to be online for the update audit of each task,and in this process the communication cost and the computational cost on user side are larger.On this basis,this paper proposed BTDA,namely a semi-trusted third party dynamic cloud data update audit program.In BT-DA,semi-trusted third party deals with update audit instead of user,so during the update audit process,the user can be off-line,thereby reducing the communication cost and the computational cost on user side.In addition,BTDA uses data blind and proxy re-signature technology to prevent semi-trusted third party and cloud server to obtain user sensitive da-ta,thus protecting user privacy.Experiments show that compared with the current scheme about second-level file block update,BTDA has a large reduction in both computation time and communication cost on user side.%云存储由于具有方便和廉价的优点,自诞生以来便得到了广泛应用.但与传统系统相比,云存储中的用户失去了对数据的直接控制,因此用户最关心的是存储在云上的数据是否安全,其中完整性是安全需求之一.公共审计是验证云数据完整性的有效方法.虽然现有方案不仅能够实现云数据的完整性验证,也能够支持动态数据更新审计,但它们也存在缺点,例如在执行多个二级文件块更新任务时,用户需要一直在线进行更新审计,而且在该过程中用户与云服务器的通信量和用户计算量都较大.基于此,提出了一种基于半可信第三方的动态云数据更新审计方案———BTDA.在BTDA中,用户将二级文件块更新审计任务代理给半可信第三方,因此在二级文件块更新审计过程中,用户可以离线,从而减少了用户端的通信量和计算量.另外,BTDA采用了数据盲化和代理重签名技术来防止半可信第三方和云服务器获取用户敏感数据,从而保护了用户隐私.实验表明,与目前的二级文件块更新审计方案相比,BT-DA中的用户端无论在计算时间还是通信量方面都有大幅减少.
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