Two-layered structure for optimally essential secret image sharing scheme

•We present a two-layered structure to solve (t, s, k, n) essential secret image sharing problem.•The proposed scheme is secure with minimum sharing ratios among related works.•A user-defined parameter m = 1 leads to minimum size of total shared shadows.•m = t leads to size of an essential shared shadow being twice of size of a non-essential shared shadow.

This paper presents a two-layered structure for optimally sharing a secret image among s essential and n − s non-essential shared shadows using the (t, s, k, n) essential thresholds, that t essential shared shadows and totally k shared shadows are needed to recover the secret image. The presented two-layered structure includes one user-defined parameter m to determine different kinds of optimal results. m = 1 leads to minimum size of total shared shadows (ST) and size of an essential shared shadow is close to size of a non-essential shared shadow. On the other hand, m = t leads to size of an essential shared shadow being twice of size of a non-essential shared shadow to signify the importance of an essential shared shadow. Moreover, the proposed structure overcomes the threshold fulfillment problem in Chen’s scheme (Chen, 2016). Theoretical analyses and experimental results show that the proposed scheme exhibits secure with optimal sharing ratios among related works.