Sharing an Image with Variable-size Shadows

Abstract

Most secret image sharing schemes produce shadows with an equal size including the well know Shamir’s and Thien-Lin’s approaches that are based upon polynomial interpolation. In this paper we utilize Chinese remainder theorem to design a novel threshold secret image scheme which produces shadows with different sizes. To share an image secretly among n participants, our scheme determines n relative prime moduli based upon which the image is encoded into n shadows which are distributed to the n participants such that every group of r participants could recover the image by using their shadows and moduli, while any group of less than r participants cannot. Since a shadow is a collection of the remainders of its corresponding modulus in our scheme, the size of the shadow is dependent on that of the modulus. Our scheme is more flexible then those in the literature due to the reason that by choosing a proper set of relative prime moduli the dealer is able to distribute shadows with different sizes to participants with different degrees of importance.