29-09-2014, 10:35 AM
Survey of Cheating Prevention Techniques in Visual
Cryptography
Survey of Cheating.pdf (Size: 546.22 KB / Downloads: 41)
Abstract:
Visual cryptography (VC) is a technique of encoding a secret image into share images such that stacking a sufficient
number of shares reveals the original secret image. Shares are generally presented in transparencies. So each participant holds a
transparency. The original secret image is recovered after superimposing the transparencies one to other. Basically, the performance of
visual cryptography scheme depends on different measures, like pixel expansion, security, contrast, computational complexity, accuracy,
share generated, number of secret images and type of secret images encrypted by the scheme. Most of the prior research work on VC
focuses on improving two parameters: pixel expansion and contrast. Visual cryptography (VC) has numerous applications, such as
authentication and identification, steganography, and image encryption. Horng et al. showed that cheating is possible in VC, where
some participants can betray the remaining participants by fake transparencies. So, designing cheating-prevention visual secret-sharing
(CPVSS) schemes has been proposed by many researchers to overcome cheating problem from existing VC. Intent of this paper is on
study and performance analysis of the cheating prevention visual cryptography schemes and cheating problem in VC and extended VC.
Introduction
Naor and Shamir, in 1994 developed one of the best-known
techniques known as visual cryptography. Visual
cryptography is a cryptographic technique which allows
visual information in the form of pictures, text, etc. to be
encrypted in such a way that decryption does not require any
computational devices and is done by the human visual
system. Their research demonstrated a visual secret sharing
scheme, where a secret image was split up into ‘n’ shares so
that only someone with all ‘n’ shares could decrypt the secret
image, while any one with less than ‘n’ shares discovered no
information about the original secret image. The shares were
printed on a separate transparency, and decryption was
performed by stacking operation of the shares. When all ‘n’
shares were overlaid, the original secret image would be
seen. The fundamental properties of Visual Cryptography
are Pixel expansion, Contrast and Security
Cheating Prevention in Visual
Cryptography Scheme
Jana, B et al [5] introduced Cheating prevention in Visual
Cryptography using steganographic Visual scheme. The
Visual Cryptography (VC) is a technique to encrypt a secret
image into transparent shares such that stacking a sufficient
number of shares reveals the secret image without any
computation. Cheating is possible in the Visual
Cryptographic Schemes (VCS) by dishonest or malicious
participant called a cheater, may provide a Fake Share (FS)
to cheat the other participants. To achieve cheating
prevention in VC we have proposed a steganographic
scheme to embed a secret message in each of the shares in
random location during share generation phase called stego
share. Before stacking operation the receiver can extract
hidden message from stego share image for checking
authentication of share images. In this method no
verification share image is required to prevent cheating in
VC.
. Conclusion
In this paper various cheating prevention schemes are
studied and their performance is evaluated on the basis of
contrast. While selecting cheating prevention method in
visual cryptography or in EVCS it must be space and time
efficient. The cheat-preventing schemes are either not robust
enough or still improvable. An efficient transformation of
VCS for cheating prevention incurs minimum overhead on
contrast and pixel expansion. It only added two sub pixels
for each pixel in the image and the contrast is reduced only
slightly. Cryptographic schemes are very useful for realizing
information security. The goal of cryptanalysis is to find
potential weaknesses in a cryptographic scheme. There are
many topics that deserve further investigations, e.g., to give
formal definition of the security of CPVSS schemes and to
design secure yet practical CPVSS schemes based on share
authentication. It processes faster due to less traversal steps
and minimizes the effect of Cheating. Participants colluding
problem is solved in Co cheating prevention scheme with
trusty third party.