Unus pro omnibus: Multi-Client Searchable Encryption via Access Control
Jiafan Wang, Sherman S. M. Chow · 2024
Searchable encryption lets an untrusted cloud server store keyword-document tuples encrypted by writers and conduct keyword searches with tokens from readers.Multi-writer schemes naturally offer broad applicability; however, it is unclear how to achieve the distinctive features of single-writer systems, namely, optimal search traversing only the result set and forward privacy invalidating old search tokens against any new data.Cutting-edge results by Wang and Chow (Usenix Security 2022) incur extra traversal over existing keywords and weaken forward privacy that only invalidates previous-issued search tokens periodically.We propose delegatable searchable encryption (DSE) with optimal search time for the multi-writer multi-reader setting.Beyond forward privacy, DSE supports security measures countering new integrity threats by malicious clients and keyword-guessing attacks inherent to public-key schemes.These are simultaneously made conceivable via one-time delegations of updating and/or searching power from the data owner and our tailored notion of shiftable multi-recipient counter encryption.DSE also benefits from the hybrid searchable encryption idea of Wang and Chow but at a microscopic level.Our evaluation confirms the order-ofmagnitude improvement in search time over real-world datasets.