Extended Functionality in Verifiable Searchable Encryption

When outsourcing the storage of sensitive data to an (untrusted) remote server, a data owner may choose to encrypt the data beforehand to preserve confidentiality. However, it is then difficult to efficiently retrieve specific portions of the data as the server is unable to identify the relevant information. Searchable encryption has been well studied as a solution to this problem, allowing data owners and other authorised users to generate search queries which the server may execute over the encrypted data to identify relevant data portions. However, many current schemes lack two important properties: verifiability of search results, and expressive queries. We introduce Extended Verifiable Searchable Encryption (eVSE) that permits a user to verify that search results are correct and complete. We also permit verifiable computational queries over keywords and specific data values, that go beyond the standard keyword matching queries to allow functions such as averaging or counting operations. We formally define the notion of eVSE within relevant security models and give a provably secure instantiation.