Addressing escalating threats: a secret image sharing scheme with adjustable threshold resilience against external adversaries and colluding participants

We propose a novel threshold changeable secret image sharing (TCSIS) scheme based on univariate and asymmetric bivariate polynomials for securing greyscale and colour secret images in the semi-honest model. The proposed scheme supports increasing the threshold number of shares needed to reveal the secret image using the share update mechanism. Unlike the existing TCSIS schemes, the proposed scheme can prevent the revealing of a secret image before the end of its lifespan. This revelation is possible due to the increasing capabilities of an external adversary and the increasing number of colluding participants. Furthermore, in contrast to some existing TCSIS schemes, each share generated using the proposed scheme does not leak visual information about the secret image. We prove the properties of the proposed scheme using theoretical analysis. We also provide experimental results supporting the implications of theoretical analysis corresponding to the execution time and the randomness of shares.