Size Invariant Visual Cryptography Schemes With Evolving Threshold Access Structures

In this research, we consider the evolving threshold access structure, denoted as
$(k, \infty)$
, for size invariant visual cryptography scheme (SIVCS). The so-called
$(k, \infty)$
threshold indicates the number of participants is supposed to be infinite and the access structure would be dynamically adjusted at any time by adding or deleting participants. First of all, the concept and definition of
$(k, \infty)$
-SIVCS are described. Shadow construction, constituted by random number generators and their choosing probabilities, for the
$(k, \infty)$
-SIVCS is then given. A contrast-maximizing problem for determining the generators and choosing probabilities is built based on the
$(k, \infty)$
-SIVCS. A simulated annealing-based algorithm is introduced to solve the optimization problem. The best solution from the simulated annealing-based algorithm forms a feasible
$(k, \infty)$
-SIVCS. To further improve the visual quality, a
$(k, \infty)$
-SIVCS using Boolean XOR decryption is also presented. Experimental results and comparisons are shown, demonstrating that the proposed techniques are feasible and advanced in the aspects of shadow size and contrast.