data hiding in intermediate significant bit planes
TRANSCRIPT
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Data Hiding in Intermediate Significant Bit Planes,
A High Capacity Blind Steganographic Technique
Shabir A. Parah
Post Graduate Department of
Electronics and Instrumentation
Technology, University of Kashmir
Srinagar, India
Javaid A. SheikhPost Graduate Department of
Electronics and Instrumentation Technology, University of Kashmir
Srinagar, India
G.M. Bhat University Science Instrumentation
Center,
University of Kashmir, Srinagar
Abstract — The availability of relatively inexpensive digital
products coupled with the promise of higher bandwidth and
quality of service (QoS) for both wired and wireless
communication networks have made it possible to create,
replicate, transmit, and distribute digital data without any loss in
quality. In such a scenario steganography has received huge
attention from the research community round the globe, as it has
been found useful for information security and under cover
communication. Stegnography refers to covert communication
for transfer of confidential information over a communication
channel. This paper presents a high capacity stegnographic
technique in which secret data is embedded in Intermediate
Significant Bit planes of the cover image. The data to be
embedded is broken down in blocks of relatively decreasing
lengths and each block is embedded in the cover media under
control of a highly secure key. This work shows attractive results
with respect to imperceptibility and capacity when compared
with a few reported techniques in addition to providing adequatedata security.
Keywords- Embedding; Intermediate Significant Bit; Covert-
communication; Steganography.
I. I NTRODUCTION
Stegnography is a type of hidden communication that
literally means “covered writing” [1]. It has been derived from
Greek words stegano means “covert” and graphos means “to
write” The rapid development of technology has increased the
horizon of communication via various wired and wirelessnetworks specially internet. This has resulted in serious
challenges pertaining to integrity and security of data beingcommunicated. Stegnography in such a scenario is being used
to avert adversaries. The goal of steganography is to hide
information inside a harmless cover medium in such a way
that it is not possible even to detect that a secret messageexists in cover medium [2]. Although encryption has been one
of the solutions for information security, but encrypted
messages once intercepted, can easily provide clue to the
adversary or enemy that some message of importance is being
communicated. Steganography, on the other hand, takes
opposite approach and attempts to hide all evidence that
communication is taking place. The issue of critical
importance, in steganography is that, the very presence of a
hidden message in the cover medium must be concealed. Sucha requirement is not critical in watermarking problems.
Security, capacity, imperceptibility and robustness are
essential features of a data hiding system. In this paper we
assume that adversary is passive, as such emphasis has been
given to high hiding capacity coupled with imperceptibility
and security. Rest of the paper is organized as follows. Section
II provides information related application areas of datahiding. Section III provides an insight into data hiding system
features. Section IV differentiates blind and non blind data
hiding systems. In section V literature survey regarding high
capacity data hiding techniques has been presented. Section VI
provides complete description of proposed work. The results
obtained in the proposed technique and the comparison withexisting ones is presented in section VII. The paper concludes
in section VIII.
II. DATA HIDING APPLICATIONS
Data hiding encompasses both digital watermarking and
steganography has been found useful in following areas:
A. Copyright Protection: To protect copyrights and assert
ownership of a Multimedia content. Generally a signature
called watermark is inserted in the medium that is to be
protected against copyright infringments.
B. Content Authentication:The use of fragile water marks is
made for content authentication. Content authentication isused to verify authenticity of a multimedia content and
ensure whether same piece has been received that was
transmitted at transmitter or a changed version of original
piece.
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embedding the payload into the low intensity pixels and hence
maximum utilization of cover image.
Development of spatial domain stegnographic techniques
for gray scale images has been reported in [13]. The schemes
are reported to have high hiding capacity and goodimperceptibility properties. The authors have discussed the
key issues pertaining to data hiding in detail. [14] Reports a
high capacity data embedding scheme based on average
covariance of the Discrete Cosine Coefficients (DCT). The
Most significant Bit (MSB) of the payload is embedded intocover image based on average covariance of cover image. A
Peak Signal to Noise Ratio (PSNR) of 46.31% for hiding
capacity of 12.50% has been reported for test image size
512x512.
An Intermediate Significant Bit (ISB) replacement based
watermarking technique has been reported and presented in[15]. The authors have reported that embedding information in
the intermediate significant bits improves robustnesscompared to data hidden in least significant bits. [16] Reports
a high capacity data hiding technique based on spatial domain.
The host image is partitioned into non-over lapping blocks,with each block containing three 3x3 pixels. In every block
these pixels receive special treatment, with an aim to decrease
the noise and deviations from the original picture values. The
authors have reported PSNR values ranging between 27db to
30db for hiding capacity of 20-26.6%.
Most of the reported techniques emphasize upon highcapacity and are less descriptive about security of payload. In
the proposed technique both the aspects capacity and security
have been given due consideration.
VI. PROPOSED METHODE
The block diagram of proposed high capacity stegnographic
system using ISB data embedding is shown in Fig. 1. Firstly,
Cover image is prepared for data embedding by breaking it
into its constituent bit planes as shown in Fig. 2. The
philosophy behind data embedding in the proposed system is,
more significant the bit plane, lesser the amount of data
embedded in it. This philosophy ensures better perceptualqualities of the stego image. As such data to be embedded in
the bit planes has been divided into three variable length data
vectors of continuously decreasing lengths. The embedding
strategy is depicted in Fig.2. As shown the data vector with
total length is divided into three variable length data vectors,
viz: and of continuously decreasing magnitude.
The data is embedded in the first three ISB planes under the
control of a private key. In order to thwart the adversary data
is not embedded sequentially. The key, which is generated
using Pseudo Random Number Generator (PRNG), ensures a
highly randomized data embedding in the three given bit planes. This process is depicted in Fig. 3. The embedding
process is carried out in data embedder, that outputs an image
containing secret data and is generally termed as stego-image.
The security of data embedded is a function of Key Length.
The used pseudo random number generator (PRNG) is capable
of addressing all the locations in first three Intermediate
Significant Bit planes where data is to be embedded. As such
the PRNG uses 18 bit seed word to generate the key forembedding data.
A. Embedding Strategy and relationship between length
of data vectors : The proposed data hiding system,
breaks the data vector to be embedded, in smaller size
vectors equal, in number to the number of ISB planes in
which data is to be hidden. The lengths of data vectors can
be related in several ways. In the implemened technique
the data has been broken into three blocks with lengths L1,L2 and L3. This is because data is to be embedded in three
ISBs. The relation between the lengths of data blocks is
L1= L/2, L2= 3L/8 and L3=L/8; where L is the total length
of data vector to be embedded in the cover medium. Thedata is embedded in the embedder under the control of a
private key. B. Extraction Strategy: The embedding algorithm uses
private key to embed the data in the ISBs of cover image.
The resultant image yeilded by data embedder is called
stego image. At the receiving end the the extraction
algorithm uses stego-image along with same key as that
used at embedder to extract data from the stego-image.
Since cover image is not needed for the retrieval of secret
data the proposed system falls in the category of blind
detection.
Fig. 1: Proposed high capacity data hiding and corresponding blind
extraction system
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Fig. 2: Data embedding strategy
Fig.3: Data embedding using Random Key
VII. R ESULTS AND A NALYSIS
The requirements of a data hiding system when used for
stegnographic purposes are of twofold viz, high hiding
capacity and imperceptibility. The two parameters
unfortunately are of opposing nature. This is because
embedding more and more data in a cover image results in
deterioration of the cover image quality, and as such an
adversary could easily guess that some data has beenembedded in the cover image. Keeping in view these
conflicting features a reasonable amount of data has been
taken to be embedded in the cover medium so as to keep
degradation in the image quality minimum. For the testing the
efficacy of the proposed scheme a set of nine standard grey
scale test images (512 x512) were used. Table 1 shows all the
used test images with their corresponding stego-image,
besides showing hiding capacity (HC) also termed as payload
and PSNR in decibels in each case. Table 2 presents details of
subset of host test images with amount of percentage dataembedded and corresponding peak signal to noise ratio PSNR.
In all cases the embedding capacity has been fixed as at 25%
that comes out to be (262144x2 bits of payload) except testimage ‘lake’ where the payload of 31.25% has been choosen.
Further a comparison of the proposed data hiding scheme with
that of Zeki et. al [16] can be seen in table 2. Table 3 showsgraphical comparison between the proposed technique and that
of Zeki et. al. The hiding Capacity (HC) and PSNR have been
calculated as follows.
A. Hiding Capacity (HC): The amount of data that can be
embedded in a cover image without deteriorating integrity
of the cover image gives an idea about the hiding
capacity. It is also referred to as payload. Hiding capacity
is represented by bits per pixel (bpp). It is given by (totalnumber message bits/total number of image bits)
multiplied by 100. If n and N respectively denote total
message bits and image bits the hiding capacity is given
by
Hiding Capacity (HC) = (n/N)*100
B. Peak Signal to Noise Ratio (PSNR): It is an important
image, objective, quality index. It is actually a measure of
quality of image when external data is embedded in it. It
gives an idea about how much deterioration has
embedding caused to the image. It is represented as
Where ‘mse’ is mean square error and is given by
Where N and M are image dimensions, and represent
original and stego images respectively.
TABLE I. VARIOUS TEST IMAGES AND THEIR STEGO VERSIONS
Details of host image, its stego version, PSNR and percentage
of data embedded
Host Image Stego Image
Boats Boats, HC=25%,
PSNR=37.50db
Peppers Peppers, HC=25%,PSNR=37.65 db
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Airplane Airplane, HC=25%PSNR=37.63 db
Lake Lake, HC=31.25%
PSNR=36.08 db
Barbara Barbara, HC=25%PSNR=37.59 db
Milk drop Milk drop, HC=25%PSNR=37.48 db
CameramanCameraman, HC=25%,PSNR=37.97 db
Baboon Baboon, HC=25%,
PSNR=37.64 db
Lena Lena, HC=25%,PSNR=37.55 db
TABLE II. CAPACITY VERSUS PSNR OF VARIOUS TEST IMAGES OF
PROPOSED ALGORITHM
TABLE III. COMPARISON BETWEEN PROPOSED AND ZEKI [16] TECHNIQUE
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VIII. CONCLUSION
A secure and high capacity data hiding technique with blind
detection is presented in this paper. The image in which the
data is embedded has been broken into its constituent bit
planes. The data to be embedded in the cover medium has been divided into three variable length data vectors. The datavectors are subsequently embedded in first three ISB planes
using a private key generated by Pseudo Random Number
Generator (PNRG). The PRNG not only embeds data pseudo
randomly in various bit planes but it also ensures
pseudorandom embedding of data at various pixel locations,
thus providing an adequate security to the data carried by the
cover image. The technique has been implemented using
MATLAB 7. The proposed technique, on an average provides
about 8db improvement in PSNR when compared with [16]
even when payload is increased on an average by 2.2%. The
results clearly show that the proposed technique has a better
performance.
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