Visual Cryptography

Two layers are combine

Visual Cryptography is very special type of encryption, proposed by Noni Noar and Adi Shamir. It allows a message or drawings, hidden in an image, to be decrypted by the human eye, and without the need for an encryption device, a computer or performing calculations by hand. For the recipient, it is the most simple and yet absolutely secure system.

In Visual Cryptography, two transparent images are created: one layer with random pixels, and a second layer with the secret information. Visual Cryptography works with layers with either identical or complementary pixels, a visual version of XOR-ing. Reading the information is only possible when both layers are aligned exactly on top of each other.

If true (crypto secure) randomness is used to generate the pixels for the first layer, it can be seen as a one-time pad system. In this case, retrieving the secret information from one of the layers is impossible if not in possession of the other layer, and Visual Cryptography offers absolute security.

More on Visual Cryptography on my website. Dutch reader can go to this page.