Decentralized multi-client boolean keyword search for encrypted cloud storage

In multi-client searchable symmetric encryption (MC-SSE), multiple clients have the capability to conduct keyword searches on encrypted data hosted in cloud, where the outsourced data is contributed by a data owner. Unfortunately, all known MC-SSE addressing key escrow problem required establishing a secure channel between data owner and user, and might suffer from significant key storage overhead. Therefore, we present an effective decentralized MC-SSE (DMC-SSE) system without the key escrow problem for secure cloud storage, eliminating the secure channel between data owner and data user. In DMC-SSE, each client independently picks its public/secret key, while a bulletin board of user public keys takes the place of the central authority. Technically, we introduce a semi-generic construction framework of DMC-SSE, building upon Cash et al.’s OXT structure (CRYPTO 2013), which roughly combines Kolonelos, Malavolta and Wee’s distributed broadcast encryption scheme (ASIACRYPT 2023) and additionally introduces a distributed keyed pseudorandom function module for securely aggregating each client’s secret key.