# Visual cryptography Author: Monika Agrawal, February 10, 2015 – Posted in: Security – Tags: Cryptography, Visual cryptography ShareTweet+1Share

Visual cryptography (VC) was introduced by Moni Naor and Adi Shamir at EUROCRYPT 1994.
Visual cryptography is a cryptographic technique which allows visual information (pictures, text, etc.) to be encrypted in such a way that decryption becomes a mechanical operation that may or may not require a computer.
It is used to encrypt written material (printed text, handwritten notes, pictures, etc) in a perfectly secure way.
OR- Visual Cryptography
Divide image into two parts
Separately, they are random noise
Combination reveals an image
k out of n sharing problem
k out of n sharing problem
For a set P of n participants,  a secret image S is encoded into n shadow images called shares (shadows), where each participant in P receives one share.
The original image is visible if any k or more of them are stacked together, but totally invisible if fewer than k transparencies are stacked together.
k out of n example (k=3,n=4)
General k out of k Scheme
In k out of k, the image is visible only if all the shares are stacked together.
If any share in k is lost, and remaining shares are stacked together, it will not form the image.
Thus, in k out of k, all the shares are important
to construct the image.
2 out of 2 Scheme (2 subpixels)
X-OR Visual Cryptography
It is a type of cryptography technique in which we encode image in such a way that we get original image after decoding.It is not possible in normal cryptography technique.Decoding can be done by human visual system or directly with the help of computer