Security in Medical Images using enhanced
Visual Secret Sharing Scheme
Kalaivani Pachiappan, Dr.Sabari Annaji, Nithya Jayakumar
Department of Information Technology,
K.S.Rangasamy College of Technology,
Tiruchengode.
E-mail: kalaivani.pachiappan@gmail.com
which allows visual information (e.g. printed text,
Abstract:
Information security has emerged as foremost
handwritten notes and pictures) to be encrypted in
challenge. Visual cryptography is one type of security
such a way that the decryption can be performed by
technique used for image encryption.
The Visual
the human visual system, without the aid of
cryptographic technique sharing of images is limited with
computers. Visual cryptography scheme eliminates
two shares. Visual secret sharing scheme is used to embed
the information. The embedded image constructs the two
shared images and have more secured than traditional
visual cryptography. The Pixel expansion is a major issue
complex computation problem in decryption process,
and the secret images can be restored by stacking
operation. This property makes visual cryptography
in Visual Secret Sharing (VSS) schemes. The various VSS
especially useful for the low computation load
schemes with minimum pixel expansion have been
requirement.
proposed for binary secret images. This paper presents a
Noar and Shamir [2] is introduced Visual
probabilistic (2, 3)-VSS scheme for gray scale images. Its
cryptography and proposed encoding scheme to share
pixel expansion is larger in size but the quality of the image
a binary image into two shares Share1 and Share2. If
is perfect when it’s reconstructed. The construction of the
pixel is white or black, then any one row chosen from
shadow images is based on the binary OR operation.
Keywords: Visual
Cryptography.
sharing, Secret sharing, Grayscale,
Figure 1 to generate Share1 and Share2. Here each
share pixel p is encoded into two white and two black
pixels each share alone gives no clue about the pixel
p whether it is white or black. Secret image is shown
INTRODUCTION
only when both shares are superimposed.
With the rapid enhancement of network
technology, multimedia information is transmitted
over the Internet conveniently. It is therefore
important to secure data over open and unsecured
networks in order to ensure safety of sensitive data.
In Medical, patient information are sensitive and
needed to be protect during storage, especially in the
cloud, and during transmission. Hence the usage of
cryptography in the protection of data is very crucial.
Visual cryptography is a cryptographic technique
Figure 1: Code Book
decryption angle. According to this graph and the
RELATED REVIEW
Chin-Chen Chang et al [16] suggested
hiding a binary image into two meaningful shares in
pre-defined visual pattern set, two shares are
generated.
spatial-domain image hiding schemes. These two
Tzung-Her Chen et al [20] offered the
secret shares are embedded into two gray level cover
multiple image encryption schemes by rotating
images. To decode the hidden messages, embedding
random grids, without any pixel expansion and
images
the
codebook redesign. A non-expansion reversible
performance between pixel expansion and contrast
visual secret sharing method that does not need to
Liguo Fang [17] recommend a (2, n) scheme based on
define the code book offered by Fang [21]. To
combination. Threshold visual secret sharing schemes
encode four secrets into two shares and recovering
mixed XOR and OR operation with reversing and
the
based on binary linear error correcting code was
Zhengxin Fu et al [22] intended a rotation visual
suggested
The
cryptography scheme. Rotation visual cryptography
disadvantage of the above schemes is that only one set
scheme construction was based on correlative
of confidential messages can be embedded, so to share
matrices set and random permutation, which can be
large amounts of confidential messages several shares
used to encode four secret images into two shares.
have to be generated.
Jonathan Weir et al [23] suggested sharing multiple
can
by
be
superimposed.
Xiao-qing
and
Balancing
Tan
[16].
reconstructed
images
without
distortions
S J Shyu et al [24] were first researchers to
secrets using visual cryptography. A master key is
advise the multiple secrets sharing in visual
generated for all the secrets; correspondingly, secrets
cryptography. This scheme encodes a set of n ≥ 2
are shared using the master key and multiple shares
secrets into two circle shares. Then secrets can be
are obtained
obtained one by one by stacking the first share and
A grayscale image is an image in which the
the rotated second shares with n different rotation
value of each single pixel is carries only amount
angles. To encode unlimited shapes of image and to
information. The darkest shade is black, and the
remove the limitation of transparencies to be circular,
lightest possible shade is white. According to their
Fang[18] offered reversible visual cryptography
physical characteristics, various ways to represent the
scheme. In this scheme two secret images which are
color level of images. The computer screen uses the
encoded into two shares; one secret image appears
electric current to control lightness of the pixels. The
with just stacking two shares and the other secret
diversity of the lightness generates different color
image appears with stack two shares after reversing
levels. The general printers can only control a single
one of them. Jen-Bang Feng et al [19] developed a
pixel to be printed (black pixel) or not to be printed
visual secret sharing scheme for hiding multiple
(white pixel), instead of displaying the gray level. As
secret images into two shares. This scheme analyzes
such, the way to represent the gray level of images is
the secret pixels and the corresponding share blocks
to use the density of printed dots. The method that
to construct a stacking relationship graph, in which
uses the density of the net dots to simulate the gray
the vertices denote the share blocks and the edges
level is called “halftone” and transforms an image
denote two blocks stacked together at the desired
with gray level into a binary image before processing.
Every pixel of the transformed halftone image has
Two-out-of-Three Scheme using Grayscale Images
only two possible color levels (black or white).
This proposed scheme is entirely different
Because human eyes cannot identify too tiny printed
from that of earlier schemes. Here the shares are
dots and, when viewing a dot, tend to cover its
designed using code book, so that when combining
nearby dots, we can simulate different gray levels
any two shares will reveal the original bit
through the density of printed dots, even though the
information, but not the whole share just half of each
transformed image actually has only two colors –
single share will produce the high quality image
black and white.
when reconstructed. This scheme can be explained by
Visual secret sharing (VSS) schemes [1][4],[12] have been proposed only with black and
taking a value from the grayscale block and divide
that value into shares as shown in the Figure 2.
white (binary) images. Several schemes for grayscale
images [14] and for color images [13], [15] have
254: [1 1 1 1 1 1 1 0]
been proposed. However, these earlier works result in
a decrypted image of less quality with pixel
1st half
2nd half
expansion. A new gray-level visual cryptography
Share1:
01010100
11011010
scheme is used to overcome problem of pixel
Share2:
10101010
11101110
expansion. Comparatively, Image quality is better
Share3:
00100100
10010100
than other schemes and provides high quality images
including that of original quality to be reconstructed.
Table-1: Grayscale bits are transformed into Binary
bits
The generation of the shared images is based on
Boolean operations, and the reconstruction operation
Share1 (1st half): 0 1 0 1 0 1 0 0
uses OR, as in other VSS schemes.
Share2 (1st half): 1 0 1 0 1 0 1 0
PROPOSED METHOD
In the proposed scheme convert each
grayscale block into a binary block. Initially each
pixel value in a grayscale block is transformed into
binary representation. For example consider a
grayscale block which is transformed into binary
1 1 1 1 1 1 1 0 = 254
Share3 (1st half): 0 0 1 0 0 1 0 0
Share1 (2nd half): 1 1 0 1 1 0 1 0
1 1 1 1 1 1 1 0 = 254
blocks.
100
[254
44
158
11
210
22
198]
110
Its corresponding binary blocks are as follows:
[0 1 1 0 0 1 0 0] [1 0 0 1 1 1 1 0] [0 0 0 1 0 1 1 0];
[1 1 1 1 1 1 1 0] [0 0 0 0 1 0 1 1] [1 1 0 0 0 1 1 0];
[0 0 1 0 1 1 0 0] [1 1 0 1 0 0 1 0] [0 1 1 0 1 1 1 0];
Share2 (2nd half): 1 1 1 0 1 1 1 0
Share3 (2nd half): 1 0 0 1 0 1 0 0
1 1 1 1 1 1 1 0 = 254
Medical
image
Convert
into binary
image
Using
code book
Build shared
images
Shared 1
1st Half
2nd Half
Shared 2
1st Half
Original
image
2nd Half
Shared 3
1st Half
Original
image
2nd Half
Original
image
Figure2: System Architecture
Combining any two half shares will provide the
If the direct shares are combined a perfect gray scale
exact bit and by doing the same procedure for the
image cannot be obtained. If it combines the half
whole grayscale block will output perfect high
shares, the original quality of the image will be
quality image when reconstructed without any loss of
revealed without any loss of generality.
contrast.
Simulation Results for 2-out-of-3 Visual Secret
sharing Scheme using Grayscale
Orginal image 128 X 128
Share1(1st half)
&
Share2(1st half)
Share 1
Share 2
Share3(1st half)
&
Share1(2nd half)
Share3
Figure 3: Generating three separate shared transparencies
for gray-level visual cryptography
Share2(2nd half) & Share3(2nd half)
Figure 4: Stacking of gray-level visual cryptography
CONCLUSION
This paper proposed a probabilistic 2-out-of3 visual secret sharing scheme for grayscale images
and gives a high quality images that of perfect
(original) quality to be reconstructed. In this scheme
the quality of the image is maintained perfectly
without any loss of generality. The size of the
shadow is increased drastically, which represents the
pixel expansion problem.
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