Cheating Human Vision in Visual Secret Sharing

Visual Secret Sharing (VSS), first introduced by Naor and Shamir, is a variant form of secret sharing; especially, secret decoding is stacking shares together without performing any complicated cryptographic computation. The recovered secret is visible by human vision system (HVS). However, Horng et al. showed cheating is possible in VSS, which is inspired from cheating in secret sharing. Since then many cheating activities and cheating immune schemes have been proposed, whereas all presented cheating activities only take cheating in any pixel as a unit into consideration. In this paper, we analyze some presented cheating activities, and we propose a new kind of cheating: Region Cheating Attack (RCA) as a result of the properties of HVS. Differently, RCA involves with cheating in a region which is several adjacent pixels as a unit. We therefore use RCA to enhance effect of several attacks which has been proposed. Moreover, a new attack, deterministic white-to-black attack (DWtBA), is proposed to point out that a well-known cheating immune scheme, proposed by De Prisco and De Santis, will suffer from RCA and DWtBA. Finally, we propose a remedy to overcome the problem of the scheme.