An improved cloud data sharing scheme with hierarchical attribute structure

Cloud computing is an emerging computing paradigm that can provide storage resources and computing capacities services over the internet. however,some new security issues arise when users’ sensitive data are outsourced and shared in untrusted cloud. the traditional techniques to protect the confidentiality of sensitive data stored in cloud are encryption and related cryptographic tools. and the corresponding private keys to access and decrypt the files are disclosed to only authorized users. however,these traditional solutions are not scalable because the computational cost of encryption and other access control is heavy for devices with limited computation ability. in this paper,we present a new way to implement scalable and fine-grained access control systems,which can be applied for big data in untrusted cloud computing environment. the solution is based on symmetric,efficient broadcast encryption and fine-grained attribute-based encryption (abe). in this access control system,users are able to join and revoked with broadcast encryption. an outsourced hierarchical abe scheme is first proposed in this paper to construct the access control system. the security analysis is also presented under the security model.