Random Grid based Visual Cryptography using a common share

Visual cryptography (VC) is a paradigm of cryptography which prevents a secret from being modified or destructed by using the notions of perfect cipher and the secret can be reconstructed by the human visual system. It is a cryptographic technique which can encrypt visual information, such as images and text; and can decrypt the secret without a computer (stack operation). This visual secret sharing scheme is developed by Moni Naor and Adi Shamir in 1994. Most of the visual cryptography schemes suffer from many drawbacks such as: pixel expansion, share management difficulty, poor quality recovered image etc. So this paper discusses a visual cryptography scheme using random grids, where it uses a common share to transmit n binary secrets. The binary secret image is divided into two share images (random grids) as in (2, 2) visual cryptography scheme. Here we use n+1 share images to transmit n secrets and the extra share is common to all n secrets. Since RG is used it creates shares without pixel expansion. This scheme can be viewed as a modified scheme of (2, 2) random grid based visual cryptography. One share is considered as a common share to all n secrets, so it makes efficient network bandwidth utilization.