Efficient visual secret sharing scheme for color images

Abstract

A k -out-of- n visual secret sharing scheme (VSSS) resolves the visual variant of the k-out-of- n secret sharing problem where only k or more out of n participants can reveal the secret by human visual system without any cryptographic computation. The best pixel expansion of the general k-out-of- n VSSS for c-colored images was c × m by Yang and Laih [New colored visual secret sharing schemes, Des Codes Cryptogr. 24 (2000) 325–335] where m is the pixel expansion of an existing binary k-out-of- n VSSS. Regarding the c-colored n-out-of- n scheme, the best pixel expansion is ( c - 1 ) 2 n - 1 - c + 2 and c ( c - 1 ) 2 n - 2 - c when n is odd and even, respectively, by Blundo et al. [Improved schemes for visual cryptography, Des Codes Cryptogr. 24 (2001) 255–278]. In this paper, we propose a new c-colored k-out-of- n VSSS by using a pixel expansion of ⌈ log 2 c ⌉ × m that is more efficient than ever.