Multi-user cloud-based secure keyword search

We propose a multi-user Symmetric Searchable Encryption (SSE) scheme based on the single-user Oblivious Cross Tags (OXT) protocol (Cash et al., CRYPTO 2013). The scheme allows any user to perform a search query by interacting with the server and any θ−1 ‘helping’ users, and preserves the privacy of database content against the server even assuming leakage of up to θ − 1 users’ keys to the server (for a threshold parameter θ), while hiding the query from the θ − 1 ‘helping users’. To achieve the latter query privacy property, we design a new distributed key-homomorphic pseudorandom function (PRF) that hides the PRF input (search keyword) from the ‘helping’ key share holders. By distributing the utilized keys among the users, the need of constant online presence of the data owner to provide services to the users is eliminated, while providing resilience against user key exposure.