Details

A modulo-4 arithmetic is graphically implemented by overlaying half-opaque/half-transparent hexagons. The 4 possible discrete relative rotations of overlaid hexagonal elements provide 4 "levels of grey". The hexagons tessellate the encrypted and key planes. The correlations between the hexagons in the encryption with the randomly rotated hexagons in the key reveal the image. Of course, for secrecy the key must be secured. Increase resolution for better effect.