Secure display by use of multiple decoding masks based on visual cryptography

A securing information display has been realized by use of multiple decoding masks based on visual cryptography. The decoding masks are used for the key for decryption. Use of physical keys are secure against cyber attacks including computer virus and spy ware. In order to secure the physical keys against theft, the number of decoding masks is increased. Code sets have been constructed to encrypt a binary image so that information on a secret image is shared between a displayed image and multiple decoding masks. The key is shared between plural users. The secret is represented only when all shared masks are overlaid in front of the displayed image. Optical decryption and limitation of the viewing zone have been demonstrated with a displayed image shown on a liquid crystal display (LCD) and decoding masks in front of the LCD. The viewed image is secure against prying eyes behind the viewer.