Privacy Preserving Dynamically Indexed Multi-Phrase Search over Encrypted Data

With the widespread usage of Cloud Computing model in business, organizations prefer to outsource their data to the cloud. In order to preserve confidentiality of data, the data is encrypted before being outsourced. In order to use this encrypted data in decision making, symmetric searchable encryption is employed that enables users to fetch data matching the keywords over encrypted data without decrypting the data. Many existing schemes search for a single keyword without an index, leading to search time linear to the size of data. And moreover, support for multiple keyword searches or phrase search is also a trending challenge in the field of searchable encryption. In this paper, we extend the practical techniques for searches on encrypted data proposed by Song, et.al, by improving the search efficiency with help of an encrypted and dynamic index. We use a very efficient structure to enable dynamic updates to the index in event of changes to the encrypted dataset. Our proposed scheme is the first one to use such a simple yet update-efficient structure for index. Multi-phrase search being implemented helps in obtaining most representative documents for searches, especially in mobile devices. We also implemented and analyzed efficiency of Song et al scheme, which is one of the pioneering works in field of searchable encryption. Security analysis and extensive experiments were conducted to test the security guarantees and efficiency of the proposed extensions.