Visual cryptography is a form of secret sharing requiring only human vision to decrypt a secret image, based on the stacking of seemingly random shadow images, or "shares". The main optimization metrics are pixel expansion and recovered image contrast. Maximization of the latter is crucial, as it determines the quality of the decrypted secret. This paper proposes genetic algorithms to evolve basis matrices striving for maximal contrast. They are encoded as binary chromosomes and an objective function is proposed to evaluate their respective fitness values. Evidence for the optimality of GA parameters is demonstrated experimentally, and the success this approach is shown with up to four shares. Furthermore, the algorithm is extended to a generalized graph access for comparison with other research, and the security of this method is analyzed and confirmed.

Evolution of Visual Cryptography Basis Matrices with Binary Chromosomes

In this study, we propose a novel design for (3, n)-threshold visual cryptography by using the theory of the combinatorics to achieve an excellent contrast (visual effects) in the stacked image. Compared to the related works, this study has the following advantages: (1) the design concept is simple and easy to implement; (2) the stacked image’s contrast is optimal when we choose n–n+1 positions to fill 1 in the columns of the dispatching matrices that are needed in applying the theorem of visual cryptography and the restored image’s contrast is better than other researches in the field of (3, n)-threshold visual cryptography; (3) our method is suitable for any types of images; (4) the size of the transparencies are the same as the secret image.

A novel approach for (3, n)-threshold visual cryptography

Visual secret sharing is a cryptographic paradigm encrypting images into a number of individually random “shadow images”. When stacked, they reveal a contrast-reduced version of a secret image. In this paper, we consider random grid shadow images, which have gained increasing attention in recent years due to lack of pixel expansion inherent in Naor-Shamir visual cryptography. We propose a methodology to use such grids to encode series of frames comprising short animations, useful in situations when a mere static image is insufficient to convey a secret instruction. Although this method results in significant contrast degradation with longer animations, a method is devised to isolate the signal from the noise in a computational XOR-based decryption.

AnimVSS: Frame-Based Visual Secret Sharing

In this study, we propose a novel design for (3, n)-threshold visual cryptography by using the theory of the combinatorics to achieve an excellent contrast (visual effects) in the stacked image. Compared to the related works, this study has the following advantages: (1) the design concept is simple and easy to implement; (2) the stacked image's contrast is optimal when we choose n-n 0.5 +1 positions to fill 1 in the columns of the dispatching matrices that are needed in applying the theorem of visual cryptography and the restored image's contrast is better than other researches in the field of (3, n)-threshold visual cryptography; (3) our method is suitable for any types of images; (4) the size of the transparencies are the same as the secret image.

Visual cryptography scheme (VCS) is a secure method that encrypts a secret image by subdividing it into shadow images Due to the nature of encryption VCS is categorized into two types: the deterministic VCS (DVCS) and the probabilistic VCS (PVCS) For the DVCS, we use m (known as the pixel expansion) subpixels to represent a secret pixel The PVCS uses only one subpixel to represent a secret pixel, while the quality of reconstructed image is degraded A well-known construction of (k, n)-PVCS is obtained from the (k, n)-DVCS In this paper, we show another construction of (k, n)-PVCS by extending the (k, k)-PVCS

Ching-Nung

Papers

Construction of General （k, n） Probabilistic Visual Cryptography Scheme