Cryptography Reference
In-Depth Information
Fig. 4.4. The eight binary planes of the gray-scale image.
where α i and β i are i-th bits of α j and β j , respectively.
In the decryption process, the scheme stacks the shadows, S 1 and S 2 ,
by using the decryption function f d LP to reconstruct the secret image. The
function f d LP is defined as follows:
1,
if α i
∈C 1
∩β i
∈C 1 ;
f d LP (S i ,S i )=
(4.4)
0,
otherwise.
Lukac and Plataniotis scheme can completely reconstruct the original se-
cret image. In their scheme, several shadows can only be used to reserve one
secret image. The utilization of the shadows is low. In this chapter, we shall
adopt Lukac and Plataniotis scheme to represent the secret image with bit-
level. Furthermore, by our method each shadow can be used to carry more
secret information.
4.3 The Proposed (2, 2)-VSS Scheme
In this section, we propose a bit-level based (2, 2)-VSS scheme to encrypt
and decrypt gray-scale images. The diagram of the proposed scheme is shown
in Fig. 4.5. Fig. 4.5(a) is the encryption process, while Fig. 4.5(b) is the
decryption process.
4.3.1 The Encryption Process
The first step of the encryption process is to divide a gray-scale image into
several sub-regions having a triangular shape. Each sub-region can be used to
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