Visual cryptography is a cryptographic technique which allows visual information i.e. pictures, text, etc. to be encrypted in such a way that decryption can be done by human visual system without the use of computers. Visual Cryptography is a visual secret sharing scheme, where an image was broken up into n shares. The individual with all the n shares only can decrypt the image, while any n-1 shares cannot reveal information about original image.

Visual Cryptography uses two transparent images: One image contains random pixels, and Other image contains the secret information. Both the transparent images are required to reveal the information. Both the layers are to be printed onto a transparent sheet, which thus can be easily recognized by human eye.

How Visual Cryptography Works:

A plain text in the forms of images is encrypted in Visual cryptography. The encrypted text creates shares which are passed through a channel i.e. fax or email and sent to decryption process. The decryption process of Visual Cryptography contains a human visual system.

  • Each pixel of the images is divided into smaller blocks.[same number of white and black blocks] either horizontally or vertically.
  • If the pixel is divided into two, one is black and the other will be white one. If is divided into four, there will be two white and two black parts.
  • The information pixel will be completely black, also called the overlayed version of pixels.

Advantages of Visual Cryptography

  • Visual cryptography offers absolute secrecy according to the information theory.
  • There is no need of computer in order to detect the information at the receiver end in visual cryptography.
  • Secure ways of encrypting is possible with the help of visual cryptography.
  • Visual cryptography is simple to implement.
  • In Visual Cryptography, encryption doesn’t require any NP-Hard problem dependency.
  • Infinite computational power cannot predict the message in visual cryptography.
  • We can send cipher text in visual cryptography through fax or e-mail.
  • In Visual Cryptography, decryption algorithm is not required. Therefore a person unknown to cryptography can decrypt the message.

Applications of Visual Cryptography

  • Visual cryptography is used in bank customer identification.
  • Anti spam-bot measure can be done by visual cryptography.
  • Visual cryptography is used in electronic voting machines/ remote voting machines to verify receipts.
  • Visual cryptography has wide range of applications in both private and public sectors of our society.
  • Visual Cryptography is used for making colored digital watermarks.