Multipartite secret sharing by bivariate interpolation

Given a set of participants that is partitioned into distinct compartments, a multipartite access structure is an access structure that does not distinguish between participants that belong to the same compartment. We examine here three types of such access structures - compartmented access structures with lower bounds, compartmented access structures with upper bounds, and hierarchical threshold access structures. We realize those access structures by ideal perfect secret sharing schemes that are based on bivariate Lagrange interpolation. The main novelty of this paper is the introduction of bivariate interpolation and its potential power in designing schemes for multipartite settings, as different compartments may be associated with different lines in the plane. In particular, we show that the introduction of a second dimension may create the same hierarchical effect as polynomial derivatives and Birkhoff interpolation were shown to do in [13].