Secret Image Sharing Revisited: Forbidden Type, Support Type, and Their Two Approaches

In this paper, we introduce two new image-sharing types to extend the applicability of sharing. Type 1 is our so-called forbidden type. In its sharing system, any t of the n shares can recover the secret image, unless the t shares form a forbidden group listed in a forbidden list. Type 2 is our so-called cross-department support type. If a government has 3 departments {DEPH, DEPM, DEPL}, then 3 thresholds (tH, tM and tL) exist. Any tH number of officers from department DEPH can unveil the secret image, and likewise for any tM and tL number of officers from departments DEPM and DEPL, respectively. Type 2 image sharing allows a secret to be disclosed not only in an intra-department meeting but also in a cross-department meeting. In this study, both types are implemented through two approaches: the polynomial and linear-equations approaches. Hackers can be confused when two approaches are mixed. As for the applications, use Type 1 to protect sensitive information in medical or military images or legal documents; and use type 2 to support cross-department crime investigation, industrial production, etc.