Visual cryptography

Visual cryptography makes it possible to encrypt the information in the form of white and black pixels. Decryption can be done only by using the optical perception, in particular the help of computers required.

The first visual encoding method was developed in 1994 by Moni Naor and Adi Shamir. Is a visual secret sharing technique in which an image is decomposed into sub-images. Any amount of frames does not allow any conclusions on the original. Each sub-image is printed on a transparent film. The decryption is performed by superposing all the parts.

Example

If each pixel of the original image is encoded randomly as described above, each film itself is a random collection of blocks. Only through knowledge of both foils information can be obtained over the original.