Secure Information Display with Two Limited Viewing Zones Using Two Decoding Masks Based on Visual Secret Sharing Scheme

We propose a secure display technique using visual cryptography. The proposed technique ensures the security of visual information. Encrypted information is perceived when viewed through a mask pattern that is composed of dot patterns of a decoding key. In order to improve security of the decoding key, the proposed display technique employs two decoding masks. Without both decoding masks, the encrypted information presented on a display cannot be decoded. We have developed a set of encryption codes so that information of a secret image can be shared among two decoding masks and a displayed image. The pixel arrangements of the decoding masks and the displayed image are designed to provide two limited viewing zones. Each viewing zone is limited by the stacked decoding masks in front of the display so that only one person can view the information at each viewing zone.