Journal of Theoretical and Applied Information Technology

2005 - 2010 JATIT & LLS. All rights reserved.

www.jatit.org

MULTI LAYER INFORMATION HIDING -A BLEND OF

STEGANOGRAPHY AND VISUAL CRYPTOGRAPHY
JITHESH K , 2Dr. A V SENTHIL KUMAR .

Asstt Prof., Department of Computer Science, Mahatma Gandhi College, Iritty, Kerala, India-670703
2
Lecturer, Department of Computer Science, Hindustan College of Science & Commerce,
Coimbatore-641006, Tamil Nadu.

ABSTRACT
This study combines the notion of both steganography [1] and visual cryptography [2]. Recently, a
number of innovative algorithms have been proposed in the fields of steganography and visual
cryptography with the goals of improving security, reliability, and efficiency; because there will be always
new kinds of threats in the field of information hiding. Actually Steganography and visual cryptography are
two sides of a coin. Visual cryptography has the problem of revealing the existence of the hidden data
where as Steganography hides the existence of hidden data. Here this study is to suggest multiple layers of
encryption by hiding the hidden data. Hiding the hidden data means, first encrypting the information using
visual cryptography and then hide the share/s[3] into images or audio files using steganography. The
proposed system can be less of draw backs and can resist towards attacks.
Keywords: Stenography, Visual Cryptography, Share, Discrete Cosine Transform(DCT).
1. INTRODUCTION TO STEGANOGRAPHY
An important sub division of information
hiding is steganography [1]. While cryptography
[4] is about protecting the content of messages,
steganography is about concealing their very
existence.
This
modern
adaptation
of
steganographia (Trithemius, 14621516), assumed
from Greek, literally means "covered writing" and
is usually interpreted to mean hiding information in
other information.
1.1 Steganography Methods[1]
There are only three ways to hide a digital
message in a digital cover: injection, substitution,
and generation of new files.

Substitution

Normal data is replaced or substituted with

the secret data. This usually results in very little
size change for the host file. However, depending
on the type of host file and the amount of hidden
data, the substitution method can degrade the
quality of the original host file.

Generation of New Files

A cover is generated for the sole purpose

of concealing a secret message. A sender creates a
picture of something innocent that can be passed to
receiver; the innocent picture is the cover that
provides the mechanism for conveying the
message.

Injection

Data injection embeds the secret message

directly in the host medium. The problem with this
kind of embedding is that it usually makes the host
file larger, and therefore the alteration is easier to
detect.

1.2 Techniques of Steganography

In all methods of steganography, something is
done to conceal a message; naturally, these actions
or techniques can be separated and analyzed to
learn what is happening during the whole process.
The six categories of steganography are:
1.
Substitution system techniques
2.
Transform domain techniques
3.
Spread spectrum techniques

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2005 - 2010 JATIT & LLS. All rights reserved.
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4.
5.
6.

Statistical method techniques

Distortion techniques
Cover generation techniques

1.3 Principles of Steganography

The "classic" model for invisible communication
was first proposed by Simmons as the "prisoners'
problem"[1]. Alice and Bob are arrested for some
crime and are thrown in two different cells. They
want to develop an escape plan, but unfortunately
all communications between each other are
arbitrated by a warden named Wendy. She will not
let them communicate through encryption and if
she notices any suspicious communication, she will
place them in solitary confinement and thus
suppress the exchange of all messages. So both
parties must communicate invisibly in order not to
arouse Wendy's suspicion; they have to set up a
subliminal channel. A practical way to do so is to
hide meaningful information in some harmless
message: Bob could, for instance, create a picture
of a blue cow lying on a green meadow and send
this piece of modern art to Alice. Wendy has no
idea that the colors of the objects in the picture
transmit information.
Figure-1

The prisoners' problem, illustrated.

Unfortunately there are other problems which may
hinder the escape of Alice and Bob. Wendy may
alter the message Bob has sent to Alice. For
example, she could change the color of Bob's cow
to red, and so destroy the information; she then acts
as an active warden. Even worse, if she acts in a
malicious way, she could forge messages and send
a message to one of the prisoners through the
subliminal channel while pretending to be the other.
The above model is generally applicable to many
situations in which invisible communication
steganographytakes place. Alice and Bob
represent two communication parties, wanting to

exchange secret information invisibly. The warden

Wendy represents an eavesdropper who is able to
read and probably alter messages sent between the
communication partners cryptographic techniques
try to conceal the contents of a message,
steganography goes yet a bit further: it tries to hide
the fact that a communication even exists. Two
people can communicate covertly by exchanging
unclassified messages containing confidential
information. Both parties have to take the presence
of a passive, active or even malicious attacker into
account.
2. VISUAL CRYPTOGRAPHY [9][10]
There are many powerful secret-sharing schemes
that enable you to encode a document or file so that
nobody can decipher the real contents of the
encoded document without access to the encrypted
shares and a computer to perform the calculations
necessary to decrypt the secret document. Visual
Cryptography is a secret-sharing method that
encrypts a secret image into several shares but
requires neither computer nor calculations to
decrypt the secret image. Instead, the secret image
is reconstructed visually: simply by overlaying the
encrypted shares the secret image becomes clearly
visible.
Visual Cryptography is a special encryption
technique to hide information in images in such a
way that it can be decrypted by the human vision if
the correct key image is used. The technique was
proposed by Moni Naor and Adi Shamir in 1994.
Visual Cryptography uses two transparent images.
They demonstrated a visual secret sharing scheme,
where an image was broken up into n shares so that
only someone with all n shares could decrypt the
image, while any n-1 shares revealed no
information about the original image. Each share
was printed on a separate transparency, and
decryption was performed by overlaying the shares.
When all n shares were overlaid, the original image
would appear. One image contains random pixels
and the other image contains the secret information.
It is impossible to retrieve the secret information
from one of the images. Both transparent images
and layers are required to reveal the information.
The easiest way to implement Visual
Cryptography is to print the two layers onto a
transparent sheet. When the random image contains
truly random pixels it can be seen as a One-time
Pad system and will offer unbreakable encryption.
In the overlay animation you can observe the two

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Journal of Theoretical and Applied Information Technology

2005 - 2010 JATIT & LLS. All rights reserved.
www.jatit.org

layers sliding over each other until they are

correctly aligned and the hidden information
appears.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, without the aid of computers.
Visual cryptography is a popular solution
for image encryption. Using secret sharing
concepts, the encryption procedure encrypts a
secret image into the so-called shares which are
noise-like secure images which can be transmitted
or distributed over an unreliable communication
channel. Using the properties of the human visual
system to force the recognition of a secret message
from overlapping shares, the secret image is
decrypted without additional computations and any
knowledge of cryptography. Visual cryptographic
solutions operate on binary or binarized inputs.
Therefore, natural (continuous-tone) images must
be first converted into halftone images by using the
density of the net dots to simulate the original gray
or color levels in the target binary representation.
Then, the halftone version of the input image is
used instead of the original secret image to produce
the shares. The decrypted image is obtained by
stacking the shares together. Because binary data
can be displayed either as frosted or transparent
when printed on transparencies or viewed on the
screen, overlapping shares that contain seemingly
random information can reveal the secret image
without additional computations or any knowledge
of cryptographic keys. However, due to the nature
of the algorithm, the decrypted image is darker,
contains a number of visual impairments, and most
of visual cryptography solutions increase the spatial
resolution of the secret image. In addition, the
requirement for inputs of the binary or dithered
nature only limits the applicability of visual
cryptography.
Most of the existing secret sharing schemes are
generalized within the so-called {k,n}-threshold
framework that confidentially divides the content of
a secret message into n shares in the way that
requires the presence of at least k, for kn, shares
for the secret message reconstruction, Thus, the
framework can use any of n!/(k!(nk)!) possible
combinations of k shares to recover the secret
message, whereas the use of k1 or less shares
should not reveal the secret message.

Figure-2

Encryption using visual cryptography

2.1 How Visual Cryptography Works
Each pixel [5] of the images is divided into
smaller blocks. There are always the same number
white (transparent) and black blocks. If a pixel is
divided into two parts, there are one white and one
black block. If the pixel is divided into four equal
parts, there are two white and two black blocks.
The example images from above uses pixels that
are divided into four parts.
If a pixel, divided into four parts, can have six
different states. If a pixel on layer 1 has a given
state, the pixel on layer 2 may have one of two
states: identical or inverted to the pixel of layer 1. If
the pixel of layer 2 is identical to layer 1, the
overlayed pixel will be half black and half white.
Such overlayed pixel is called grey or empty. If the
pixels of layer 1 and 2 are inverted or opposite, the
overlayed version will be completely black. This is
an information pixel.
We can now create the two layers. One
transparent image, layer 1, has pixels which all
have a random state, one of the six possible states.
Layer 2 is identical to layer 1, except for the pixels
that should be black (contain information) when
overlayed. These pixels have a state that is opposite
to the same pixel in layer1. If both images are
overlayed, the areas with identical states will look
gray, and the areas with opposite states will be
black.
The system of pixel can be applied in different
ways. In our example, each pixel is divided into
four blocks. However, you can also use pixels,
divided into two rectangle blocks, or even divided
circles. Also, it doesn't matter if the pixel is divided
horizontally or vertically. There are many different
pixel systems, some with better contrast, higher
resolution or even with color pixels.
If the pixel states of layer 1 are truly (crypto
secure) random, both empty and information pixels

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2005 - 2010 JATIT & LLS. All rights reserved.
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of layer 2 will also have completely random states.

One cannot know if a pixel in layer 2 is used to
create a grey or black pixel, since we need the state
of that pixel in layer 1 (which is random) to know
the overlay result. If all requirements for true
randomness are fulfilled, Visual Cryptography
offers absolute secrecy according to the
Information Theory.
If Visual Cryptography is used for secure
communications, the sender will distribute one or
more random layers 1 in advance to the receiver. If
the sender has a message, he creates a layer 2 for a
particular distributed layer 1 and sends it to the
receiver. The receiver aligns the two layers and the
secret information is revealed, this without the need
for an encryption device, a computer or performing
calculations by hand. The system is unbreakable, as
long as the two layers don't fall together in the
wrong hands. When one of both layers is
intercepted it's impossible to retrieve the encrypted
information.

the case of visual cryptography is, we need no

computation to decrypt the encrypted data. It can be
well perceived through human visual system
(HVS). What we need is only the required number
of shares of the original information which is
divided into number of shares when encrypted.
Previously the methodology used for encrypting
information
is
either
cryptography
or
steganography. But here we used both. The
algorithm is as follows. First the information which
is going to be transmitted is encrypted using visual
cryptography. So there we achieve first level of
security. Then this crypt is embedded into natural
or artificial image/images, which is steganography.
That gives second level of security.
4. STEGANOGRAPHY ALGORITHMS
A number of steganographic algorithms are
available but only one of them adopted in this study
are explained in detail below
4.1 Steganography in the DCT Domain [1]

3. METHODOLOGY USED
PROPOSED SYSTEM

FOR

THE

For this study the existing methods are analyzed.

A few techniques are there to implement both
steganography and visual cryptography. Among
them an optimal one can be find out by analyzing
and verifying the existing tools, which are
implemented using the known techniques. Each one
has got there own pros and corns. Using the
existing methods of both steganography and visual
cryptography a novel algorithm is suggested in this
paper. That is, as aforementioned, combining both
steganography and visual cryptography. It can be
made better match for sending hidden information.
As, mentioned both steganography and
cryptography have pros and corns. Whenever they
are using independently we could only have single
level of security. That can easily be broken by
eavesdroppers. If we could combine the features of
both together then we would have two levels of
security. That is, in a simple way we can say hiding
hidden data, which ensure multi [9] level of
security.
So as we suggest blending of both steganography
and visual cryptography. The steganography
technique used here is DISCRET COSINE
TRANSFORM TECHNIQUE [DCT] [8] [14], the
most reliable type of steganography technique and
the new type of cryptography technique which is
VISUAL CRYPTOGRAPHY. The main advantage
of DCT is, it is very robust. Similarly, the merit in

One popular method of encoding secret

information in the frequency domain is modulating
the relative size of two (or more) DCT coefficients
within one image block. We will describe a system
which uses digital images as covers and which is
similar to a technique proposed by Zhao and
Koch.[10]
Algorithm 1. DCT-Steg encoding process
for i = 1, , (M) do
choose one cover-block bi
Bi = D {bi}
if mi = 0 then
if Bi(u1, v1) > Bi(u2, v2) then
swap Bi(u1, v1) and Bi(u2, v2)
end if
else
if Bi(u1, v1) < Bi(u2, v2) then
swap Bi(u1, v1) and Bi(u2, v2)
end if
end if
adjust both values so that |Bi(u1, v1) - Bi(u2, v2)| >
x
bi = D-1{Bi}
end for
create stego-image out of all bi
During the encoding process, the sender splits the
cover-image in 8x8 pixel blocks; each block
encodes exactly one secret message bit. The

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embedding process starts with selecting a

pseudorandom block bi which will be used to code
the ith message bit. Let Bi = D{bi} be the DCTtransformed image block.
Before the communication starts, both sender and
receiver have to agree on the location of two DCT
coefficients, which will be used in the embedding
process; let us denote these two indices by (u1, v1)
and (u2, v2). The two coefficients should correspond
to cosine functions with middle frequencies; this
ensures that the information is stored in significant
parts of the signal (hence the embedded information
will not be completely damaged by JPEG
compression). Furthermore, we can assume that the
embedding process will not degenerate the cover
heavily, because it is widely believed that DCT
coefficients of middle frequencies have similar
magnitudes. Since the constructed system should be
robust against JPEG compression, we choose the
DCT coefficients in such a way that the
quantization values associated with them in the
JPEG compression algorithm are equal.
One block encodes a "1," if Bi(u1, v1) > Bi(u2, u2),
otherwise a "0." In the encoding step, the two
coefficients are swapped if their relative size does
not match with the bit to be encoded. Since the
JPEG compression can (in the quantization step)
affect the relative sizes of the coefficients, the
algorithm ensures that |Bi(u1,v1) - Bi(u2,v2)| > x for
some x > 0, by adding random values to both
coefficients. The higher x is, the more robust the
algorithm will be against JPEG compression,
however, at the expense of image quality. The
sender then performs an inverse DCT to map the
coefficients back into the space domain. To decode
the picture, all available blocks are DCTtransformed. By comparing the two coefficients of
every block, the information can be restored.
Embedding and extraction algorithms are outlined
later .

Algorithm 2. DCT-Steg decoding process

for i = 1, , (M) do
get cover-block bi associated with bit i
Bi = D{bi}
if Bi(u1, v1) Bi(u2, v2) then
mi = 0
else
mi = 1
end if
end for

If the constant x and the location of the used DCT

coefficients are chosen properly, the embedding
process will not degenerate the cover visibly. We
call expect this method to be robust against JPEG
compression, since in the quantization process both
coefficients are divided by the same quantization
values. Their relative size will therefore only be
affected in the rounding step.
Perhaps the most important drawback of the
system presented above is the fact that Algorithm 1
does not discard image blocks where the desired
relation of the DCT coefficients cannot be enforced
without severely damaging the image data
contained in this specific block.
Zhao and Koch proposed a similar system which
does not suffer from this drawback. They operate
on quantized DCT coefficients and use the relations
of three coefficients in a block to store the
information. The sender DCT transforms the image
block bi and performs a quantization step to get BQi.
One block encodes a "1," if BQi(u1, v1) > BQi(u3,
v3) + D and BQi(u2, v2) > BQi(u3, v3) + D. On the
other hand, a "0" is encoded, if BQi(u1, v1) + D <
BQi(u3, v3) and BQi(u2, v2) + D < BQi(u3, v3). The
parameter D accounts for the minimum distance
between two coefficients for representing an
embedded bit; normally D = 1. The higher D is, the
more robust the method will be against image
processing techniques. Again, the three selected
coefficients should be situated in the middle of the
spectrum.
In the encoding step, the relations between these
three coefficients are changed so that they represent
one bit of the secret information. If the
modifications required to code one secret bit are too
large, then the block is not used for information
transfer and marked as "invalid." This is the case, if
the difference between the largest and the smallest
coefficient is greater than some constant value MD.
The higher MD is, the more blocks can be used for
communication. In order to allow a correct
decoding, the quantized DCT coefficients of an
invalid block are changed so that they fulfill one of
the two conditions

BQ i (u1,v1)<=BQ i(u3,v3)<=BQ i(u2,v2)

BQ i (u2,v2)<=BQ i(u3,v3)<=BQ i(u1,v1)
Afterwards the block is dequantized and the inverse
DCT is applied.
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The receiver can restore the information by

applying DCT and quantizing the block. If the three
selected coefficients fulfill one of the conditions,
the block is ignored. Otherwise the encoded
information can be restored by comparing BQi(u1,
v1), BQi(u2, v2), and BQi(u3, v3). The authors claim
that this embedding method is robust against JPEG
compression (with quality factors as low as 50%),
since all changes are made after the "lossy"
quantization step.

Construct a
initial matrix IM on ground set A =
{1,2,,k} such that the columns of
IM are all of the distinct n-tuples that
contain each element of A exactly n0
/k times.
Construct a (k, k)-threshold VCS with
basis matrices T0 and T1.

5. VISUALCRYPTOGRAPHY ALGORITHMS
5.1 Construction Algorithm for a (2, 2)Threshold Scheme

Build
basis matrices
R0 and R1 by replacing each element i
(1 i k) in IM with the ith row of T0
and T1, respectively.

Build
basis matrices
S0 and S1 by restricting R0 and R1,
respectively, to their first n rows.
This construction generates a VCS
with relative contrast (m) =
(n0/k)k/(2k-1(n0 nCr k).

General Requirement

Construct two 2x2 basis matrices as:

S0 =

10
,
01

Using the permutated basis matrices,

each pixel from the secret image will
be encoded into two subpixels on each
participant's share. A black pixel on
the secret image will be encoded on
the ith participant's share as the ith row
of matrix S1, where a 1 represents a
black subpixel and a 0 represents a
white subpixel. Similarly, a white
pixel on the secret image will be
encoded on the ith participant's share
as the ith row of matrix S0.
Before encoding each pixel from the
secret image onto each share,
randomly permute the columns of the
basis matrices S0 and S1.
This VCS (Visual Cryptography
Scheme) divides each pixel in the
secret image into m=2 subpixels.
It has a contrast of (m)m=1 and a
relative contrast of (m)=1/2.

S1 =

10
10

5.3 Construction Algorithm for a (k, n)Threshold Scheme

General Requirement

Let

6. ALGORITHM FOR THE PROPOSED

SYSTEM
6.1 Encoding Process

114

Choose Information to be encrypted,

say Mi.
Using the aforementioned algorithm
of visual cryptography, divide the
content of the message (Mi) into n
shares (here we get first level of
hiding)
Each share will be treated as
information.
Shares can be treated as a single
image or different.
If shares are treating as a single image
we can hide it together inside a single
Image. Else we need different images
to different shares.
Select an appropriate image or
images so that the shares of the
original message can be embedded in
to a single image or each share in
different images.
Instead of sending the n shares
immediately it will be embedded into
an image or images using any of the

Journal of Theoretical and Applied Information Technology

2005 - 2010 JATIT & LLS. All rights reserved.
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steganography technique. (Here we

get second level of hiding).

7.2 Level 2 Hiding using steganography

Figure-4

If we are using different images to

store different shares it will be much
secure and very difficult to find out
the information by the intruders. But
need different Images.

Use DCT-Steg encoding process to

encrypt the shares[which comprises
the secret data]

6.2 Decoding Process

Use DCT- Steg decoding process to

decrypt the shares from images

After decoding the message from the

cover medium [Here image/images]
we will get the n shares of the
message. They are in encrypted form.
That is encrypted by visual
cryptography.
These n shares can then be decrypted
by human visual system, without the
aid of computers. We need no
computing mechanism to decrypt the
message
encrypted
by
visual
cryptography. What we only need is
to super impose all the n shares on
one another so that we will get the
original message.

7.

Share 1Embedded Image

Figure-5

Share 2 Embedded Image

7.3 Extracted Shares from Images

EXPERIMENTAL RESULT

Figure-6

7.1 Level 1 hiding using Visual

Cryptography
Figure 3

Secret Data

share 1

7.4 Super Imposing Share1 and

Share2 to Form the Original Secret
Data

share 2

The secret Information

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8. CONCLUSION AND FURTHER

DEVELOPMENT
This project implemented the steganography,
visual cryptography and the combination of both.
This project allows the authorized users to work.
The algorithm developed can be used depending on
the situation and application.
The proposed system is aimed to simplify the
complex and redundant process with the flexibility
of a simple process. The proposed system is being
developed as an attempt to overcome the
difficulties of the existing system.
The following are the merits of the proposed
system.
It provides two levels of security to the
information being transmitted. That is the
intruders cannot easily break the system.
Even if they realize the existence of a secret
data they cannot easily recognize the data,
since data is hidden in two ways.
This system overcomes the demerits of using
single level of hiding. That is either using
cryptography or steganography.
And one more thing to add is it requires only
the computation time of single level hiding,
because visual cryptography requires no
computation to decrypt the information.
The implemented algorithm can be used in the
following areas
In military and navy to make their
communication secure
In payment gate way.
In medical production system for secret
products
In business dealing and settlement
contracts
In electronic mail communication
9.

SCOPE FOR FURTHER DEVELOPMENT

The proposed algorithm can be implemented in

the following area of applications.
Pictorial database
Photo image
Video image
Audios
Email server message

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Norwood.
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BLUNDO AND CLEMENTE GALDI1
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[1].Stefan Katzenbeisser ,Fabien A. P. Petitcolas
Information Hiding Techniques for
Steganography and Digital Watermarking

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