Biblio

The sensitivity of a function is the maximum change of its output for a unit change of its input. In this paper we present a method for determining the sensitivity of SQL queries, seen as functions from databases to datasets, where the change is measured in the number of rows that differ. Given a query, a database schema and a number, our method constructs a formula that is satisfiable only if the sensitivity of the query is bigger than this number. Our method is composable, and can also be applied to SQL workflows. Our results can be used to calibrate the amount of noise that has to be added to the output of the query to obtain a certain level of differential privacy.

We present improved protocols for the conversion of secret-shared bit-vectors into secret-shared integers and vice versa, for the use as subroutines in secure multiparty computation (SMC) protocols and for protocols verifying the adherence of parties to prescribed SMC protocols. The protocols are primarily designed for three-party computation with honest majority. We evaluate our protocols as part of the Sharemind three-party protocol set and see a general reduction of verification overheads, thereby increasing the practicality of covertly or actively secure Sharemind protocols.