Better Security for Queries on Encrypted Databases

Private database query (PDQ) processing has received much attention from the fields of both cryptography and databases. While previous approaches to design PDQ protocols exploit several cryptographic tools concurrently, recently the appearance of fully homomorphic encryption (FHE) schemes enables us to design PDQ protocols without the aid of additional tools. However, to the best of our knowledge, all currently existing FHE-based PDQ protocols focus on protecting only constants in query statements, together with the client\u27s data stored in the database server. In this paper, we provide a FHE-based PDQ protocol achieving better security, protecting query types as well as constants in query statements for conjunctive, disjunctive, and threshold queries with equality comparison. Our contributions are three-fold: First, we present a new security definition that reflects our enhanced security model which additionally protects query types in query statements. Second, we provide a new design for PDQ protocols using FHE schemes. To do this, we come up with a method to homomorphically evaluate our encrypted target queries on the encrypted database. Thereafter, we apply it to construct a protocol and show its security under our enhanced security definition in the semi-honest model. Finally, we provide proof-of-concept implementation results of our PDQ protocol. According to our rudimentary experiments, it takes 40 seconds to perform a query on 2352 elements consisting of 11 attributes of 40-bit using Brakerski-Gentry-Vaikuntanathan\u27s leveled FHE with SIMD techniques for 80-bit security, yielding an amortized rate of just 0.12 seconds per element

SoK: Cryptographically Protected Database Search

Protected database search systems cryptographically isolate the roles of reading from, writing to, and administering the database. This separation limits unnecessary administrator access and protects data in the case of system breaches. Since protected search was introduced in 2000, the area has grown rapidly; systems are offered by academia, start-ups, and established companies. However, there is no best protected search system or set of techniques. Design of such systems is a balancing act between security, functionality, performance, and usability. This challenge is made more difficult by ongoing database specialization, as some users will want the functionality of SQL, NoSQL, or NewSQL databases. This database evolution will continue, and the protected search community should be able to quickly provide functionality consistent with newly invented databases. At the same time, the community must accurately and clearly characterize the tradeoffs between different approaches. To address these challenges, we provide the following contributions: 1) An identification of the important primitive operations across database paradigms. We find there are a small number of base operations that can be used and combined to support a large number of database paradigms. 2) An evaluation of the current state of protected search systems in implementing these base operations. This evaluation describes the main approaches and tradeoffs for each base operation. Furthermore, it puts protected search in the context of unprotected search, identifying key gaps in functionality. 3) An analysis of attacks against protected search for different base queries. 4) A roadmap and tools for transforming a protected search system into a protected database, including an open-source performance evaluation platform and initial user opinions of protected search.Comment: 20 pages, to appear to IEEE Security and Privac