03-09-2014, 11:50 AM
Visual
Visual.pptx (Size: 1.78 MB / Downloads: 10)
What is Visual Cryptography
Visual Cryptography was introduced by Moni Naor and Adi Shamir at EUROCRYPT in 1994.
It is used to encrypt written material (printed text, handwritten notes, pictures etc) in perfectly secure way.
The decoding is done by the human visual system directly, without any computation cost.
Types of visual cryptography
Halftone visual cryptography
Color visual cryptography
Visual Cryptography with Perfect Restoration
Multiresolution Visual Cryptography
Progressive Multiresolution Visual Cryptography
Halftone visual cryptography
A halftone image is made up of a series of dots rather than a continuous tone.
These dots can be different sizes, different colors, and sometimes even different shapes.
Larger dots are used to represent darker, more dense areas of the image, while smaller dots are used for lighter areas.
Visual Cryptography with Perfect Restoration
The half toning method degrades the quality of the original image.
In this technique both gray and color images are encoded without degradation.
It retains the advantages of traditional visual cryptography.
Here the stacking operation involves only XOR ing .
Multiresolution Visual Cryptography
In traditional (k , n) visual cryptography, we only construct an image of single resolution if the threshold k number of shares are available.
Progressive visual cryptography scheme in which we not only build the reconstructed image by stacking the threshold number of shares together, but also utilize the other shares to enhance the resolution of the final image.
ADVANTAGES
Simple to implement
Decryption algorithm not required (Use a human Visual System). So a person unknown to cryptography can decrypt the message.
We can send cipher text through FAX or E-MAIL
Lower computational cost since the secret message is recognized only by human eyes and not cryptographically computed.
DISADVANTAGES
The contrast of the reconstructed image is not maintained.
Perfect alignment of the transparencies is troublesome.
Its original formulation is restricted only to binary images. For colored images additional processing has to be done.
Conclusion
Among various advantages of Visual Cryptography
Schemes is the property that VCS decoding relies purely
on human visual system, which leads to a lot of
interesting applications in private and public sectors of
our society.
Visual Cryptography is used with short messages,
therefore giving the cryptanalyst little to work with.
It can be used with other data hiding techniques to provide better security.