Secure mediation of join queries by processing ciphertexts

In a secure mediated information system, confidentiality is one of the main concerns when transmitting data from datasources to clients via a mediator. We present three approaches that allow a mediator to compute a JOIN operation on encrypted relations; each approach uses a different encryption scheme. We adapt these schemes to the mediator architecture and provide a comprehensive description of the resulting protocols. A first security analysis is also given.