Cryptography Reference
In-Depth Information
M reg A regular mask of size (x=) (y=). This mask is only designed
for p B = p S = 50%. Fig ure 11.7 (a) shows the r egu lar mask with
the alternate blocks,
B
and
S , where a block
B
contains large
subpixels and a block S contains small subpixels.
M ran A random mask of size ( x= )(y = ). This mask is designed for any
p B and p S . At this time, B and S are randomly chosen according
p B and p S , as shown in Figure 11.7(b).
D B ()
Let A = [a i;j ] , where a i;j is the element of the i-th row and j-th
column in A, be a matrix in C 1 or C 0 . The function D B () divides
a secret pixel s into m large subpixels (bp) j ( (bp) j = 0 denotes
white and (bp) j = 1 denotes black) in the i-th share, 1 i n and
1 j m, dened as follows:
(bp) j = a i;j in A 2 C 0 for s is the white secret pixel.
(bp) j = a i;j in A 2 C 1 for s is the black secret pixel.
D S () Similar to D B (), it divides a secret pixel into m small subpixels
(sp) j in the i-th share, 1 i n and 1 j m.
A m x ;m y () Arrangement function that randomly arranges m large (or small)
subpixels into an (m x m y )-sized rectangle where m = m x m y .
O (i) n output shares, i 2 [1;n], of size (xm x ) (ym y ).
I 0 The recovered secret image of size (xm x ) (ym y ).
D B (s) =
FIGURE 11.7
Regular and random masks for arranging the large and small subpixels: (a)
regular mask and (b) random mask.
Even though the shares use a regular mask, an attacker could not gain any
information from the mask and the secrecy is not compromised.
Encrypting Algorithm:
Input: I, 2 , p B , p S , C 0 and C 1 of a (k;n)-threshold VCS.
Output: O (i) , i 2 [1;n].
Step 1:
Obtain the large-scaled and small-scaled secret images I B and I S
from a secret image I.
 
 
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