Learning Tool

Learning Tool

Use this panel to learn more about Visual Cryptography!


What is Visual Cryptography?

Visual Cryptography is a technique that allows information (images, text, diagrams..) to be encrypted using an encoding system that can be decrypted by the eyes. No computer is required to decode.

What is Visual Steganography?

Steganography is a technique to conceal text, images, videos in a seemingly innocuous file. It makes use of unused pixels in regular computer files in order to hide another hidden text or image.

Demonstration
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Why Visual Steganography (Visual Cryptography + Steganography)?

As opposed to other forms of cryptography, visual cryptography requires the participation of the user. Decryption of the shares provide information that is only perceived visually, thus deterring automated attacks. It is akin to One Time Pad (OTP) that provides perfect secrecy, this is due to the incomplete information the attacker has to break the cipher. The Steganography technique we used allows us to make the secret less obvious and hence enhance the overall security even further.

How does it work?

This awesome technique should be attributed to two of the great Mathematicians: Moni Naor and Adi Shamir. They came out with a technique that requires the share of both parties to exists in order to decrypt the image.

left The basis of this technique is that it would overlay two semi-transparent layers on top of each other. right
Overlaying (mathematically equivalent to Binary OR operation) both of the shares creates addition interference to the light passing through it.
merged
When both of the shares are properly overlayed on top of each other, it will divulge the secret image as shown below.
result
How does Visual Steganography work?

With this technique, we are going to sub-divide each pixel into (2x2) subpixels; these pixels are randomly generated and it has to conform to the following rules: when both of the images are overlayed, we can represent the black pixels with 4 black sub-pixels and white with 3 black sub-pixels.

Black White
black white
After Expansion
4black 3black
B1B2 B1W2 W1B2 W1W2 B1B2 B1W2 W1B2 W1W2
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Mini Quiz

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How does the cleaning algorithm work?

As you can see from the interactive animation above, only shares with 4 sub-pixels would be interpreted as black, any lesser than that (3 sub-pixels) would be interpreted as white colour. This step would convert those (2x2) subpixels into one pixel based on the algorithm used above.



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