Paper 2024/2091

Encrypted Multi-map that Hides Query, Access, and Volume Patterns

Abstract

We present an encrypted multi-map, a fundamental data structure underlying searchable encryption/structured encryption. Our protocol supports updates and is designed for applications demanding very strong data security. Not only it hides the information about queries and data, but also the query, access, and volume patterns. Our protocol utilizes a position-based ORAM and an encrypted dictionary. We provide two instantiations of the protocol, along with their operation-type-revealing variants, all using PathORAM but with different encrypted dictionary instantiations (AVL tree or BSkiplist). Their efficiency has been evaluated through both asymptotic and concrete complexity analysis, outperforming prior work while achieving the same level of strong security. We have implemented our instantiations and evaluated their performance on two real-world email databases (Enron and Lucene). We also discuss the strengths and limitations of our construction, including its resizability, and highlight that optimized solutions, even with heavy network utilization, may become practical as network speed improves.