Size-Hiding Computation in the Honest-But-Curious Model

Size-hiding computation is a special type of secure multiparty computation that also ensures the privacy of the input/output sizes. A size-hiding class specifies which party is allowed to know which input/output sizes. A size-hiding class is said to be possible if every efficient function can be securely computed with the input/output size privacy in the class. Existing work showed the complete characterization of the (im)possibility of size-hiding classes against honest-but-deterministic (HBD) adversaries instead of honest-but-curious (HBC) adversaries which are considered to be the standard semi-honest adversaries. In this work, we show the complete characterization of the (im)possibility of size-hiding classes against HBC adversaries. In particular, we give the necessary and sufficient condition for whether a size-hiding class is possible against HBC adversaries in both the secure channel model and the strong secure channel model.