This document summarizes a mini project on generating meaningful shares in visual cryptographic systems. The project was presented by three students under the supervision of Mr. Sandeep Gurung. The document outlines the contents, introduction, aim, problem definition, analysis of the problem, solution strategy, literature survey, design strategy, test plan, implementation details, results and discussions, summary and conclusion, and references. It aims to implement a cryptographic scheme that can decode concealed images without computation by generating random parts of images and embedding them in meaningful shares that can be overlapped to decrypt the output.

1. Mini Project on
GENERATION OF MEANINGFUL SHARES IN VISUAL
CRYPTOGRAPHIC SYSTEMS
Presented
By
Uttari Chakraborty (200911117)
Debarko De (200915026)
Pratarshi Saha (200911075)
Under the supervision
of
Mr. Sandeep Gurung
(Associate Professor, CSE Dept., SMIT)
DEPT. OF COMPUTER SCIENCE AND ENGINEERING
SIKKIM MANIPAL INSTITUTE OF TECHNOLOGY
MAJITAR SIKKIM, 737136.
Dated : 07/12/2012

2. CONTENTS
1. Introduction
2.Design Strategy
3.Test Plan
4.Implementation Details
5.Results and Discussions
6.Summary and Conclusion

3. INTRODUCTION
Visual Cryptography combines perfect ciphers and
graphics
Input = Binary Image
Output = 2 (or more) shares
Shares can be printed on transparent papers
Overlapping of shares reveals the secret
No computer participation is required
Can be decoded directly by the HVS

4. AIM
To implement Generation of
meaningful shares in Visual
Cryptographic Systems

5. Problem Definition
• To share secrets without revealing the message
• A third party cannot decrypt the message if he
has less than the required number of shares
• The main areas of problem are-
The contrasts of the output images are lower
than the original secret message
To make the shares completely unsuspicious

6. Analysis of the Problem
• To extract meaningful shares out of various
kinds of images
• The schemes developed have a disadvantage of
contrast loss
• Also the randomness of the shares make them
obvious
• Hence, we have to develop a method to conceal
the shares inside meaningful images

7. Solution Strategy
• Partial images are generated of the secret
message by breaking the image into random
parts
• Distribute these parts among random images
which upon overlapping reveal the secret
message
• These partial images are embedded in
meaningful shares which make it difficult to
detect any hidden image

8. Literature Survey
Visual Cryptography and Shares
Visual Cryptography by Moni Naor and Adi Shamir, LNCS,
Springer, Heidelberg (1994)
Different schemes for generation of shares
A Comprehensive Study of Visual Cryptography by Jonathan
Weir and WeiQi Yan (Queen’s University Belfast, Belfast, BT7
1NN, UK)

9. Design Strategy
Fig:- Steps involved in accomplishing the project

10. TEST PLAN
• Should work for any kind of image-
The algorithms used in this project work for any
type, dimension or color model of image.
• Minimum contrast degradation-
The PSNR of the algorithms is calculated to
compare the unwanted contrast loss.
• Randomness in partial images
AND operation is performed on the shares to
check for randomness.

11. IMPLEMENTATION DETAILS
(2,2) SCHEME
WHITE SHARES: { }
BLACK SHARES: { }
• Each pixel is divided into 2 sub pixels
• Thereby distorts the aspect ratio of the image
• This scheme is seldom used

12. (2,4) SCHEME
Problems
Contrast Ratio gets deviated from the original
image and is almost half of that of the original
image.

13. PROPOSED SOLUTION
HALFTONING
Half toning is a method for creating the illusion of Continuous tone output in
Binary Mode.
•Error diffusion is a type of halftoning in which Quantization Residual is
distributed to neighboring Pixels that have not yet been processed.
•Error diffusion using FLYOD-STEINBERG ALGORITHM
Initialize w(x,y)
to Image(x,y)
If w(x,y)
>
threshold
Print
0
Print 1
No
Yes
Compute Error
w(x,y)-max
Forward
Distribute Error

14. Halftone Results
Original Gray Scale Image Halftone Image
Input Image Output ImageHalftoned
Comparison of (2,4) Scheme Output with and without Halftoning

15. Colour Visual Cryptography
Input ImageOuutput Image

16. RESULTS AND DISCUSSIONS

17. COMPARISON OF ALGORITHMS
PSNR Ratio is used to find out the relative execution time of different
algorithms. The formaula to calculate the PSNR is as given below:
Type of Image PSNR Value
Black & White Image
without Halftoning
6.5715 dB
Black & White Image with
Halftoning
7.3651 dB
Colour CMYK Images 7.4337 dB

18. SUMMARY AND CONCLUSION
• Thus, in this project we have implemented a new type of
cryptographic scheme which can decode concealed
images without any computation.
• We have generated random parts of various types of
images and embedded them in meaningful shares
• After generating shares using the cover image, we have
overlapped those shares to get the decrypted output.

19. REFERENCES
• Visual Cryptography by Moni Naor and Adi
Shamir, LNCS, Springer, Heidelberg (1994)
• A Comprehensive Study of Visual Cryptography
by Jonathan Weir and WeiQi Yan (Queen’s
University Belfast, Belfast, BT7 1NN, UK)

20. GANTT CHART
Project Gantt Chart
7
Aug
2012
11
Aug
2012
22
Aug
2012
15
Nov
2012
Problem
Definition
& Solution
Formulatio
n
Literature Survey
IMPLEMENTATION
Verification And
Validation
Dcumentation
20
Oct
2012

21. Thank You