IMPROVING SECURITY OF VISUAL CRYPTOGRAPHY BY CONTRAST SENSITIVITY FUNCTION

Without using complicated conventional cryptographic techniques, Visual Cryptography (VC) has been created to
encode images into multiple shares and decode them by stacking the shares. This method aims to securely transmission
of real-time images without compromising their visual quality. From this perspective, a Signific VC (SVC) method has
been suggested to generate meaningful shares from the Secret Image (SI) and embed them into the Least Significant
Bits (LSB) of the Cover Image (CI). By extracting the LSB, the SI was restored on the receiver side. But, this LSB
embedding was not vulnerable to attacks since the LSBs of the image were easily decoded by invaders. Hence, in this
article, a Secure SVC (SSVC) method is proposed which applies the Contrast Sensitivity Function (CSF) rather than
using the LSB embedding and extraction tasks. It comprises 2 different stages: share generation and reconstruction. In
the share generation stage, the SI is transformed into the Signific SI (SSI) and the shares are created. Then, the CSF is
determined to choose the blocks of the CI and the created hidden shares are implanted at random with the selected
blocks of the CI. So, semantic and meaningful shares are produced. Such embedded CI blocks are known as shares.
After that, the created shares are forwarded to the user over the transmission medium. Similarly, a key share is created
from the received shares in the reconstruction step to recreate the SI. Based on this SSVC method, the robustness of
retrieving SIs from the CI is increased. Further, the testing outcomes prove that the SSVC achieves high efficiency in
secure image transfer/access in cloud systems compared to conventional VC methods.