Visual Secret Sharing Schemes

Question

Give a brief explanation of Visual Secret Sharing Schemes.

Answer 1

Shamir and Naor developed what they called visual secret sharing schemes, which are an interesting visual variant of ordinary secret sharing schemes.

Generally speaking, the problem can be formulated as follows: There is a secret picture to be shared surrounded by n participants. The picture is separated in n transparencies (shares) such that when any m transparencies are placed together, the picture becomes observable, but when fewer than m transparencies are placed up together, nothing can be seen. Such scheme is constructed through viewing the secret picture as the set of black and white pixels and handling each pixel separately. See for more details. The schemes are completely secure and easily implemented devoid of any cryptographic computation. A further improvement provides each transparency (share) to be innocent picture (e.g. a picture of landscape or picture of building); therefore concealing the fact that secret sharing is taking place.