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INDEX

1. Visual Secret Sharing –Definition

2. Schemes in Visual Secret Sharing

3. Concept of Pixel Expansion and Contrast

4. Objective of the proposed scheme

5. Overview of the proposed scheme.

6. Proposed algorithm for videos

7. Verification of shares with the POB number system.

8. Advantages of the proposed scheme.

9. Comparison with the known results in literature.

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VISUAL SECRET SHARING

ecurity of visual data is important issue in the design

of the communication systems.

ata hiding techniques and Visual Secret Sharing are

used to introduce confidentiality and security when

visual data are transmitted through unsecured

communication channels.

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VISUAL CRYPTOGRAPHY

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PIXEL EXPANSION & CONTRAST

Two important factors used to determine the efficiency of any 

cryptographic schemes are Pixel Expansion and Contrast.The difference measure between a black and a white pixel in the

reconstructed image is called contrast .

The number of sub-pixels that each pixel of the original image is

encoded into on each transparency is termed  pixel expansion.

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[

0101

] [0110

1001

1010

[[ ]]]

Expansion = 2Contrast=(2-

1)/2=0.5

[

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CONTD..

ny loss of information during reconstruction phase

leads to the reduction in the quality of the recovered

image. This is called Contrast.

Pixel expansion refers to the number of subpixels in

the generated shares that represents a pixel of the

original input image.

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OBJECTIVES OF THE

PROPOSED SCHEME

ixel expansion must be zero

uality of the secret image should be retained in the recovered image.

he size of the share should not reveal the original size of the secret.

oseless encryption.

orrupted shares should be clearly identified before using them for decryption.

utomatic modification of shares so that if the shares are hacked after a period of 

time they should be invalid.

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OVERVIEW OF THE

ALGORITHM

earranged

Image

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Image Reshape

d Image

Encrypte

d Image

Share 1 Share k Share n

Permutation Modification Generation

 Association

1,2,.., k k, ……..,n

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DECRYPTION OF THE SHARES

tep 1: permutation matrices are defined in such a way thatthere exists only one 1 in each row and column.

tep 2: Taking the positions of 1 each row will result in K x

1 matrix for each permutation matrix. Also the each

column generator matrix to each of the shares. This

results the concept that only if k shares of secret image is

obtained it will be able to generate the generator matrix.

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ENCRYPTION OF VIDEOS

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Frame Generation

Selection of 

I-frame

Difference from I -frame to

other frames

Threshold>no. of 

difference

Store the

difference in I-

frame’s log file

Encrypt the currentI-frame

Take current frame

as next I-frame

NOYES

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VERIFICATION OF ENCRYPTED

SHARES

n cryptography, a secret sharing scheme is verifiable if auxiliary information is

included that allows players to verify their shares as consistent.

n verifiable secret sharing (VSS) the object is to resist malicious players, such as

(i) a dealer sending incorrect shares to some or all of the participants, and

(ii) participants submitting incorrect shares during the reconstruction protocol.

n standard secret sharing, the dealer is assumed to be honest.

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POB NUMBER SYSTEM FOR

VERIFICATION.

ermutation Ordered Binary (POB) Number System takes two nonnegative integral

parameters, n and r, where n >=r. The system is denoted by POB(n, r). In this number system, we represent all integers in the range 0, . . . ,n!/(n-r)! r! -1, as a binary string,

say

= bn-1, bn-2, bn-3, ….., b2, b1,b0 of length n and exactly r 1’s

ach digit of this number, say, bj is associated with its position value, given by

 j * j!/pj! (j-pj)! Where pj = ∑pi ‘i’ from 0 to j

he original values are obtained V(B)

(B) = ∑bj * j!/(j-pj)!pj! ‘j’ from 0 to n-103/07/12 Visual Secret Sharing 12

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ALGORITHM - POB

enerate POB-number corresponding to a given POB-value. In a POB(n, r) number system, if a POB-value,

value is given, the algorithm generates POB(n,r)

number :B such that V (B) = value.

nput : Three numbers: n; r and value with r <= n and

0 <= value <= n!/r!(n-r)!

utput: The POB-number B = bn-1bn-2 …. b003/07/12 Visual Secret Sharing 13

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ADVANTAGES OF THE

PROPOSED SCHEME

imple coding

ixel expansion is little with this scheme. When the k and

n values are higher pixel expansion is considerably low.

ontrast is maintained

olor darkening phenomenon is also considered with this

scheme.

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COMPARISONS WITH THE KNOWNRESULTS IN THE LITERATURE.

1 :the pixel expansion of colour (k, n)-VCS under the visual cryptography model

of Naor and Shamir 

2 : whether or not the construction is based on the halftone technique

3 : whether or not the increase in the number of colours of the recovered secret

image will increase the pixel expansion.

4 : whether or not the colour model of the construction considers the colour 

darkening phenomenon during stacking of pixels with the same colour.

5 : whether or not the recovering of the secret image requires the assistance of 

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COMPARISONS WITH THEKNOWN RESULTS IN THE

LITREATURE.Constructions C1 C2 C3 C4 C5

Ours 0 No No Yes yes

Cimato et al. N/A No Yes No No

Hou and TU 1 Yes No Yes No

Shyu et al. Log c * m No Yes No No

 Yang and chen 1 No No No No

Liu Wu lin 1 No No Yes No

  Yang and liah Cm No Yes No No

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COMPRESSION RATES

AS N AND K SHARES INCREASES PIXEL EXPANSIONCOMES DOWN TO ZERO..

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APPLICATIONS

roviding high level security for Closed Circuit Television footages and

perfect recovery.

toring vital financial documents multiple servers where each server 

stores only a part of the information.

ecuring video chat applications

powerful encryption utility that brings military strength encryption with just one

click.

edical a lications Xra ima e of a atient.

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REFERENCES

di Shamir, How to Share a Secret, Communications of the ACM, Vol. 22, no. 11,

pp. 612-613, Nov. 1979.

ohsen Heidarinejad, Amirhossein Alamdar Yazdi and Konstantinos N. Plataniotis

“Algebraic Visual Cryptography Schemes for Images” (2008).

oni Naor and Adi Shamir -Visual Cryptography (1994).

. Sreekumar and Dr. S. Babu Sundar –”An efficient secret sharing scheme for n

out of n scheme using POB –number system”.

xis Communications-H.264 Video compression standard.New possibilities within

video surveillance.(2008)03/07/12 Visual Secret Sharing 19

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 THANK YOU

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