{"ID":2885243,"CreatedAt":"2026-06-01T04:54:23.091178241Z","UpdatedAt":"2026-06-01T04:54:23.091178241Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2508.05394","arxiv_id":"2508.05394","title":"Grouped k-threshold random grid-based visual cryptography scheme","abstract":"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 $(k \\leq n'\\leq n)$, termed \\emph{$n'$-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.","short_abstract":"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 requirin...","url_abs":"https://arxiv.org/abs/2508.05394","url_pdf":"https://arxiv.org/pdf/2508.05394v1","authors":"[\"Xiaoli Zhuo\",\"Xuehu Yan\",\"Wei Yan\"]","published":"2025-08-07T13:44:09Z","proceeding":"cs.CR","tasks":"[\"cs.CR\"]","methods":"[]","has_code":false}