Multi-User Dynamic Searchable Symmetric Encryption with Corrupted Participants

—We study the problem of multi-user dynamic searchable symmetric encryption (DMUSSE) where a data owner stores its encrypted documents on an untrusted remote server and wishes to selectively allow multiple users to access them by issuing keyword search queries. Speciﬁcally, we consider the case where some of the users may be corrupted and colluding with the server to extract additional information about the dataset (beyond what they have access to). We provide the ﬁrst formal security deﬁnition for the dynamic setting as well as forward and backward privacy deﬁnitions. We then propose µ SE, the ﬁrst provably secure DMUSSE scheme and instantiate it in two versions, one based on oblivious data structures and one based on update queues, with different performance trade-offs. Furthermore, we extend µ SE to support veriﬁability of results. To achieve this, users need a secure digest initially computed by the data owner and changed after every update. We efﬁciently accommodate this, without relying on a trusted third party, by adopting a blockchain-based approach for the digests’ dissemination and deploy our schemes over the permissioned Hyperledger Fabric blockchain. We prototype both versions and experimentally evaluate their practical performance, both as stand-alone systems and running on top of Hyperledger Fabric.