Priority visual secret sharing of random grids for threshold access structures

Conventional (k, n)-threshold visual secret sharing of random grids (VSSRG) schemes generate n shares having the same average light transmission from a secret image to be shared, and any information related to the secret image cannot be identified externally from a single share held by one participant. In addition, the secret image can be recovered only by collecting k shares individually held by participants, and every share has the same capability of recovering the secret image. In fact, participants' priority levels vary in certain conditions, and therefore their shares' capabilities to recover the secret image are different. The priority-based (k, n)-threshold VSSRG scheme proposed in this study enables the assignment of different priority weights to each share to create different priority levels. During decryption, the stacking of shares with different priority levels recovers the secret image at different levels. Moreover, shares individually held by each participant have the same average light transmission, and consequently the shares' priority levels cannot be identified externally.