An Efficient Conjunctive Keyword and Phase Search Scheme for Encrypted Cloud Storage Systems

There have been increasing interest in the area of privacy-protected searching as industries continue to adopt cloud technologies. Much of the recent efforts have been towards incorporating more advanced searching techniques. Although many have proposed solutions for conjunctive keyword search, it is only recently that researchers began exploring phrase search over encrypted data. In this paper, we present a scheme that incorporates both functionalities. Our solution makes use of symmetric encryption, which provides computational and storage efficiency over schemes based on public key encryption. By considering the statistical properties of natural languages, we were able to design indexes that significantly reduce storage cost when compared to existing solutions. Our solution allows for simple ranking of results and requires a low storage cost while providing document and keyword security. By using both the index and the encrypted documents to performs searches, our scheme is also currently the only phrase search scheme capable of searching for non-indexed keywords.