EVCS-DAS: Evolving Visual Cryptography Schemes for Dynamic Access Structures

Abstract

A systematic investigation of evolving visual cryptography scheme (EVCS) is carried out in this paper. The evolving scheme, denoted as (k, ∞), differs from the (k, n) threshold in that it permits an arbitrary and perhaps unlimited number of participants. More importantly, the access structure can be updated dynamically by adding new users. First of all, a preliminary implementation strategy for the (2, ∞) EVCS is introduced. Then, by employing the (2, 2) VCS recursively with the (2, ∞) EVCS, a (k, ∞) EVCS is created. In order to enhance the performance, an improved scheme is constructed based on the multi-secret VCS (MVCS) and a series of EVCS schemes with thresholds of (1, ∞), · · · , (k − 1, ∞). Moreover, Boolean XOR operation is adopted for secret recovery to further improve the visual quality. To facilitate the XOR decryption, a novel access structure partition algorithm is presented. Additionally, the proposed partition method can successfully solve the security issue in existing multi-secret XOR-based VCS (MXVCS). By integrating the more secure MXVCS into the improved scheme, XOR decryption is provided. The two proposed methods are shown to be effective and advantageous through extensive experiments and comparisons.