  This paper proposes Prism, a secret sharing based approach to compute private
set operations (i.e., intersection and union), as well as aggregates over
outsourced databases belonging to multiple owners. Prism enables data owners to
pre-load the data onto non-colluding servers and exploits the additive and
multiplicative properties of secret-shares to compute the above-listed
operations in (at most) two rounds of communication between the servers
(storing the secret-shares) and the querier, resulting in a very efficient
implementation. Also, Prism does not require communication among the servers
and supports result verification techniques for each operation to detect
malicious adversaries. Experimental results show that Prism scales both in
terms of the number of data owners and database sizes, to which prior
approaches do not scale.
