2025/08/07 by Zhuo, Xiaoli, Yan, Xuehu, Yan, Wei · 1 citation
#Cryptography and Security (cs.CR) #FOS: Computer and information sciences
paper · doi:10.48550/arxiv.2508.05394
Visual cryptography schemes (VCSs) belong to a category of secret image sharing schemes that do not require cryptographic knowledge for decryption, instead relying directly on the human visual system. Among VCSs, random grid-based VCS (RGVCS) has garnered widespread attention as it avoids pixel expansion while requiring no basic matrices design. Contrast, a core metric for RGVCS, directly determines the visual quality of recovered images, rendering its optimization a critical research objective. However, existing (k,n) RGVCSs still fail to attain theoretical upper bounds on contrast, highlighting the urgent need for higher-contrast constructions. In this paper, we propose a novel sharing paradigm for RGVCS that constructs (k,n)-threshold schemes from arbitrary (k,n')-threshold schemes (k ≤ n'≤ n), termed n'-grouped (k,n) RGVCS. This paradigm establishes hierarchical contrast characteristics: participants within the same group achieve optimal recovery quality, while inter-group recovery shows a hierarchical contrast. We further introduce a new contrast calculation formula tailored to the new paradigm. Then, we propose a contrast-enhanced (k,n) RGVCS by setting n'= k, achieving the highest contrast value documented in the existing literature. Theoretical analysis and experimental results demonstrate the superiority of our proposed scheme in terms of contrast.