Cover Picture: Cloud services encourage individuals and enterprises to store data on external infrastructure to ensure reliability, availability, and to save costs. Despite its benefits, protecting the security and privacy of the outsourced data is a primary challenge. Data encryption retains the out-sourced data's security and privacy to some extent but it does not permit traditional plaintext keyword search mechanisms. Hence, proposing an efficient encrypted cloud data search service could be transformative. Earlier work focuses on single keyword search and even those that support multi-keyword search suffer from private information leakage when queries are performed in the cloud. This paper addresses the problem of leakless privacy-preserving multi-keyword ranked search over encrypted cloud data (LRSE), and makes novel contributions to address challenging problems of search pattern and co-occurrence information leakage in the cloud. Our method employs secure inner product similarity and a novel chaining encryption notion, which are shown to be secure and efficient providing both a high level of privacy/security and efficiency.
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