Hierarchical ID-based searchable encryption with constant size ciphertext in cloud
In a hierarchical system, a set of users with ranked rights are organized in a tree-architecture, and the user with higher grade can search and access data of users with lower grade in its branch. Nowadays hierarchical systems are constructed by utilizing the cloud to improve their performance due to the cloud server's powerful computation and storage capabilities. However, the untrusted cloud server may give rise to the risk of private information exposure. To enable ranked and controllable data search in cloud without revealing users' privacy in a hierarchical system is a challenging open problem. In this paper, we formally define the hierarchical searchable encryption, where the user in the hierarchical system can search the data of its descendants. A basic hierarchical ID-based searchable encryption (HIBSE) scheme with constant size ciphertext and probe (i.e. trapdoor) is proposed, which satisfies IND-sID-CKA security. An extended secure channel free HIBSE scheme is also given, where the user can search the data of all his descendants at one time, and it achieves IND-sID-OKGA. The performance evaluation demonstrates that the extended scheme greatly reduces the computation cost when the user searches the data of all his descendants in the branch. Therefore, the extended scheme is efficient and practical in various applications.