04-10-2012, 05:49 PM
VISUAL CRYPTOGRAPHY
visual cryptography1.ppt (Size: 2.73 MB / Downloads: 25)
What is Visual Cryptography ?
Visual cryptography is a cryptographic technique which allows visual information (pictures, text, etc.) to be encrypted in such a way that the decryption can be performed by the human visual system.
Visual cryptography was pioneered by Moni Naor and Adi Shamir in 1994
Suppose the data D is divided into n shares
D can be constructed from any k shares out of n
Complete knowledge of k-1 shares reveals no information about D
k of n shares is necessary to reveal secret data.
Basis matrices
The two matrices S0,S1 are called basis matrices, if the two collections C0,C1 as defines in [1] are obtained by rearranging the columns of S0,S1 satisfy the following condition:
the row vectors V0,V1 obtained by performing
OR operation on rows i1,i2,…..iv of S0,S1 respectively, satisfy
(V0) ≤ tX - (m) m and (V1) ≥ tX
IMPLEMENTATION
A pixel P is split into two sub pixels in each of the two shares.
If P is white, then a coin toss is used to randomly choose one of the first two rows in the figure above.
If P is black, then a coin toss is used to randomly choose one of the last two rows in the figure above.
Then the pixel P is encrypted as two sub pixels in each of the two shares, as determined by the chosen row in the figure. Every pixel is encrypted using a new coin toss.
Now let's consider what happens when we superimpose the two shares.
If P is black, then we get two black sub pixels when we superimpose the two shares;
visual cryptography1.ppt (Size: 2.73 MB / Downloads: 25)
What is Visual Cryptography ?
Visual cryptography is a cryptographic technique which allows visual information (pictures, text, etc.) to be encrypted in such a way that the decryption can be performed by the human visual system.
Visual cryptography was pioneered by Moni Naor and Adi Shamir in 1994
Suppose the data D is divided into n shares
D can be constructed from any k shares out of n
Complete knowledge of k-1 shares reveals no information about D
k of n shares is necessary to reveal secret data.
Basis matrices
The two matrices S0,S1 are called basis matrices, if the two collections C0,C1 as defines in [1] are obtained by rearranging the columns of S0,S1 satisfy the following condition:
the row vectors V0,V1 obtained by performing
OR operation on rows i1,i2,…..iv of S0,S1 respectively, satisfy
(V0) ≤ tX - (m) m and (V1) ≥ tX
IMPLEMENTATION
A pixel P is split into two sub pixels in each of the two shares.
If P is white, then a coin toss is used to randomly choose one of the first two rows in the figure above.
If P is black, then a coin toss is used to randomly choose one of the last two rows in the figure above.
Then the pixel P is encrypted as two sub pixels in each of the two shares, as determined by the chosen row in the figure. Every pixel is encrypted using a new coin toss.
Now let's consider what happens when we superimpose the two shares.
If P is black, then we get two black sub pixels when we superimpose the two shares;