Data sharing on the cloud: a scalable proxy-based protocol for privacy-preserving queries

Outsourcing data on the cloud poses many challenges related to data owners and users privacy, specially when some data processing capabilities are delegated to the cloud infrastructure. In this paper we address the problem of executing privacy-preserving equality queries in a scenario where multiple data owners outsource their databases to an untrusted cloud service provider, accepting encrypted queries coming from authorized users. We propose a highly scalable proxy re-encryption scheme so that (i) the cloud service provider can return only the encrypted data that satisfies user's query without decrypting it, and (ii) the encrypted results can be decrypted using the user's key. We analyze the computation efficiency and the security of the scheme against proxy under the standard Diffie-Hellman assumption, reporting also some experimental results, which show encouraging speed up in comparison with previously proposed similar schemes.