Paper 2022/598

Verifiable and forward private conjunctive keyword search from DIA tree

Laltu Sardar and Sushmita Ruj

Abstract

In a dynamic searchable encryption (DSE) scheme, a cloud server can search on encrypted data that the client stores and updates from time to time. Due to information leakage during the search and update phase, DSE schemes are prone to file injection attacks. If during document addition, a DSE scheme does not leak any information about the previous search results, the scheme is said to be forward private. A DSE scheme that supports conjunctive keyword search should be forward private. There has been a fair deal of work on designing forward private DSE schemes in the presence of an honest-but-curious cloud server. However, a malicious cloud server might not run the protocol correctly and still want to be undetected. In a verifiable DSE, the cloud server not only returns the result of a search query but also provides proof that the result is computed correctly. We design a forward private DSE scheme that supports conjunctive keyword search. At the heart of the construction is our proposed data structure called the dynamic interval accumulation tree (DIA tree). It is an accumulator-based authentication tree that efficiently returns both membership and non-membership proofs. Using the DIA tree, we can convert any single keyword forward private DSE scheme to a verifiable forward private DSE scheme that can support conjunctive queries as well. Our proposed scheme has the same storage as the base DSE scheme and low computational overhead on the client-side. We have shown the efficiency of our design by comparing it with existing conjunctive DSE schemes. The comparison also shows that our scheme is suitable for practical use.