Hierarchical Multi-Keyword Ranked search for secured document retrieval in public clouds

For providing efficient data security, sensitive data has to be doubly encrypted in public clouds. Recent approaches to perform the two layer encryption the data owners carry out coarse grained encryption, whereas the cloud implements a fine-grained encryption on top of the owner encrypted data. But in this for searchable encryption points, it was done using Plaintext keyword search or Single keyword search or Boolean keyword search. When large amount of data users and documents in the cloud taken into concern, it is necessary to allow multiple keywords in the search request and return documents in the order of their relevance to these keywords. In this paper, for the first time, we define and solve the problem of privacy preserving and data retrieval from encrypted data in public clouds by Double Layer Encryption (DLE) and Hierarchical Multi-Keyword Ranked Search schema (HMRS). Through these two concepts our system assures the confidentiality of the data with ranking and secures the privacy of users from the cloud. On the real-world it shows proposed schemes indeed introduce fast retrieval, more security and less cost in computation and communication in Public Cloud.