Witness indistinguishable and witness hiding protocols

Abstract

A two party protocol in which party A uses one of several secret witnesses to an NP assertion is witness indistinguishable if party B cannot tell which witness A is actually using. The protocol is witness hiding if by the end of the protocol B cannot compute any new witness which he did not know before the protocol began. Witness hiding is a natural security requirement, and can replace zero knowledge in many cryptographic protocols.