Sharing an Image with Variable-Sized Shadows

Abstract

Most secret image sharing schemes produce shadows with an equal size including the well known Shamir's and Thien-Lin's approaches that are based upon polynomial interpolation. In this paper we design a novel threshold secret image scheme which generates shadows with different sizes. To share an image secretly among n participants, our scheme depends on n pre-determined relative prime moduli to encode the image into n shadows by Chinese remainder theorem 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. Owing to the design that 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. As compared to those conventional secret image sharing schemes that produce shadows with the same size, our scheme is more flexible due to the reason that by choosing a proper set of relative prime moduli the dealer is able to generate and distribute shadows with different sizes to the participants according to their degrees of importance.