Cheating Immune Block-Based Progressive Visual Cryptography

Recently, Hou et al. Introduced a (2, n) block-based progressive visual cryptographic scheme (BPVCS), which the image blocks can be gradually recovered step by step. In Hou et al.'s (2, n)-BPVCS, a secret image is subdivided into n non-overlapped image blocks. When stacking any t (2 <= t <= n) shadows, the image blocks associated with these t participants will be recovered. Unfortunately, Hou et al.'s (2, n)-BVCPS suffers from the cheating problem, which any two dishonest participants might collude together to tamper their image blocks shared with other honest participants. Also, they can impersonate an honest participant to force other honest participants to reconstruct the wrong secret. In this paper, we solve the cheating problem and propose a cheating immune (2, n)-BPVCS.