IMAGE STEGANOGRAPHY
APROJECT REPORT
Submitted toVeer Surendra Sai University of Technology ,Burla
in partial fulfillment for the award of the degreeof
BACHELOR OF TECHNOLOGY
IN
COMPUTER SCIENCE AND ENGINEERING
By
AJIT KUMAR SATAPATHYRegd No.-0801111094
Under guidance of
Prof. Rakesh Mohanty
Degree of Computer Science and Engineering VEER SURENDRA SAI UNIVERSITY OF TECHNOLOGY
: BURLA, ODISHA,INDIA
NOV 2011
2
VEER SURENDRA SAI UNIVERSITY OF TECHNOLOGY : BURLA
BONAFIDE CERTIFICATE
Certified that this project report IMAGE STEGANOGRAPHY
is the bonafide work of AJIT KUMAR SATAPATHY who carried out the
project work under my supervision.
SIGNATURE SIGNATURE
Prof.M.R.Kabat Prof .R.K.Mohanty HEAD OF THE DEPARTMENT SUPERVISOR
COMPUTER SCIENCE AND ENGG. COMPUTER SCIENCE AND ENGG.VSSUT ,BURLA VSSUT ,BURLAODISHA ODISHA
3
TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
ABSTRACT 6
LIST OF FIGURES 7
1. INTRODUCTION 8
1.1 Steganography vs cryptography 10
1.2 Types of Steganography 10
1.2.1 Text stganography 10
1.2.1.1 Line shift coding 11
1.2.1.2 Word shift coding 11
1.2.1.3 Feature coding 11
1.2.1.4 Implementation 12
1.2.2 Image steganography 12
1.2.2.1 Least significant bits 13
1.2.2.2 Hiding the data 13
1.2.2.3 Recovery the data 13
1.2.2.4 Images detection 14
1.2.3 Audio Steganography 17
1.2.3.1 LSB Coding 17
1.2.3.2 Phase Coding 17
1.2.4 Video Steganogrphy 17
1.2.5 Need and applications of steganography 18
4
2 Literature Review 19
2.1 TextSteganography:ANovelApproach 19
2.2 Digital steganography for information security 22 2.3 Digital signature authentication 23 2.4 Digital Watermarking 23
2.5 Steganography of plain text and image 25
2.6 Morden Techniques of steganography 26 3 Multi segment steganography techniques 29
4 Conclusion 31
5
ABSTRACT OF THE PAPER
In this paper I am going to introduce steganography and types of steganography mainly
used in recent time. Mainly I am working on image steganography .first I am introduce some con-
cept on different types of steganography. Then I describe different techniques (classic as wellas
modern techniques) of Image steganography. Then how it different from cryptography. In this pa-
per I am describing the complexity of the stego key serch.I am showing the
Drawbacks of multi segment stganography techniques which used code table mechanism.
6
LIST OF FIGURES FIG.NO. TITLES PAGE NO. 1 Overview of steganography process 92 Steganography type diagram 103 Text data 154 Input image 155 Output image 166 Output image by notepad 167 Covered data 1.jpg 36.1KB stego.jpg 36.3KB
stegomessage 39.2KB 17LIST OF TABLE1 code table 22
7
1. INTRODUCTION-
The word steganography is derived from the Greek words “stegos” meaning “cover”
and “grafia” meaning “writing” ,defining it as “covered writing” . Steganography is one such pro-se-
curity innovation in which secret data is embedded in a cover . The notion of data hiding or
steganography was first introduced with the example of prisoners' secret message by Simmons
in 1983 .
In ancient Greece, people used invisible ink or even the messenger’s body to
write down messages and then hide them with wax- as a stego medium. Even earlier than the Greek
use, there have been several dated messages found and embedded within the hieroglyphics of ancient
Egyptian monuments . All these are methods used in previous years are also known as physical
steganography. Nowadays we use different computer file formats to cover the message that the
sender wants to hide. The medium used to carry the message is known as the cover medium. The
medium after embedding or hiding the message is known as a stego medium. There are four basic
cover media used nowadays for steganography purposes. The following formula (Equation 1.1) pro-
vides the idea behind the Steganographic process :
Cover medium + Hidden data + Stego_key = Stego_medium fig 1.1
This process is shown in Figure 1.1. Assume three different characters for example
Bob, Alice and Eve. Suppose Bob want to send a secret message M to Alice. So he can use one of the
steganography techniques and hide the message. To increase complexity, he can also combine cryp-
tography technique with steganography. Then Bob needs to send this stego data file to Alice. Alice
when receive this stego data file, she needs to extract the original message by applying the decoding
technique. If any eavesdropper, Eve, receive the stego data file the she is unable to detect that mes-
sage is hidden in the stego file. This is the main advantage of using steganography method in com-
munications as any third person cannotdetect that the conversation is going on.
There are few well-known text steganography methods. One is to insert the secret message into a
webpage or inside a markup language. In this method the message is hidden using html tags . In line
8
shift text steganography and in word shift text steganography the horizontal and vertical space be-
tween the two words is used to hide the message. The toughest text steganography technique is fea-
ture specific encoding, in which the characteristic of the letter is used to hide the message. There are
some feature specific text steganography techniques available for different languages, for example :
hindi characters .
Figure 1.. Overview of steganography process
9
1.1 Steganography vs Cryptography
Steganography and cryptography are closely related .Cryptography scrambles the message so they
can’t understand. Steganography hide the message that there no existence of the message in the first
place ,
When steganography fails and the message can be detected ,it is still of no use
as it is encrypted using cryptography techniques
1.2 Types of Steganography-
4 types of Steganography techniques are used that is text steganography ,image steganography,audio
and video steganography.
Fig 2 Steganography type diagram
.
steganography
Text
Image
Audio
Video
10
1.2.1Text Steganography-Text steganography can be achieved by altering the text formatting, or by altering certain
characteristics of textual elements (e.g., characters). The goal in the design of coding methods is to
develop alterations that are reliably decodable (even in the presence of noise) yet largely
indiscernible to the reader. These criteria, reliable decoding and minimum visible change, are
somewhat conflicting; herein lies the challenge in designing document marking techniques.
The document format file is a computer file describing the document content and page layout (or
formatting), using standard format description languages such as PostScript2, TeX, @off, etc.
It is from this format file that the image - what the reader sees - is generated.
The three coding techniques that we propose illustrate different approaches rather than form <an
exhaustive list of document marking techniques. The techniques can be used either separately or
jointly. Each technique enjoys certain advantages or applicability as we discuss below.
1.2.1.1Line-Shift Coding This is a method of altering a document by vertically shifting the locations of text lines to
encode the document uniquely. This encoding may be applied either to the format file or to
the bitmap of a page image. The embedded codeword may be extracted from the format file or
bitmap. In certain cases this decoding can be accomplished without need of the original image,
since the original is known to have uniform line spacing between adjacent lines within a
paragraph.
1.2.1.2 Word-Shift Coding
This is a method of altering a document by horizontally shifting the locations of words within text
lines to encode the document uniquely. This encoding can be applied to either the format file or to
the bitmap of a page image. Decoding may be performed from the format file or bitmap. The
method is applicable only to documents with variable spacing between adjacent words.
Variable spacing in text documents is commonly used to distribute white space when justifying
text. Because of this variable spacing, decoding requires the original image - or more specifically, the
spacing between words in the un-encoded document.
1.2.1.3 Feature Coding
This is a coding method that is applied either to a format file or to a bitmap image of a
document. The image is examined for chosen text features, and those features are altered, or not
altered, depending on the codeword. Decoding requires the original image, or more specifically,
11
a specification of the change in pixels at a feature. There are many possible choices of text
features; here, we choose to alter upward, vertical endlines - that is the tops of letters, b, d, h, etc.
These endlines are altered by extending or shortening their lengths by one (or more) pixels, but
otherwise not changing the endline feature .
1.2.1.4 Implementation
In the midway of this our mortal life,
I found me in a gloomy wood, astray
Gone from the path direct: and e'en to tell
It were no easy task, how savage wild
That forest, how robust and rough its growth,
Which to remember only, my dismay
Renews, in bitterness not far from death.
Yet to discourse of what there good befell,
All else will I relate discover'd there.
How first I enter'd it I scarce can say
In the midway of this our mortal life,
I found me in a gloomy wood, astray
Gone from the path direct: and e'en to tell
It were no easy task, how savage wild
That forest, how robust and rough its growth,
Which to remember only, my dismay
Renews, in bitterness not far from death.
Yet to discourse of what there good befell,
All else will I relate discover'd there.
How first I enter'd it I scarce can say
06081913030629170827 meet at dawn
12
1.2.2 Image steganography
Hiding information inside images is a popular technique nowadays. An image with a secret message
inside can easily be spread over the World Wide Web or in newsgroups. The use of steganography in
newsgroups has been researched by German steganographic expert Niels Provos, who created a
scanning cluster which detects the presence of hidden messages inside images that were
posted on the net. However, after checking one million images, no hidden messages
were found, so the practical use of steganography still seems to be limited.
To hide a message inside an image without changing its visible properties, the cover source can be
altered in ”noisy” areas with many color variations, so less attention will be drawn to the
modifications. The most common methods to make these alterations involve the usage of the least-
significant bit or LSB, masking, filtering and transformations on the cover image. These techniques
can be used with varying degrees of success on different types of image files.
1.2.2.1 Least Significant Bits
Many stego tools make use of least significant bit (LSB). For example, 11111111 is an 8-bit binary
number. The rightmost bit is called the LSB because changing it has the least effect on the value of
the number. The idea is that the LSB of every byte can be replaced with little change to the overall
file. The binary data of the secret message is broken up and then inserted into the LSB of each pixel
in the image file.
1.2.2.2 Hiding the data
Using the Red, Green, Blue (RGB) model a stego tool makes a copy of an image palette, say, an 8-bit
image. The copy is rearranged so that colors near each other in the RGB model are near each other in
the palette. The LSB of each pixels 8-bit binary number is replaced with one bit from the hidden mes-
sage. A new RGB color in the copied palette is found. A new 8-bit binary number of the new RGB
color in the original palette is found. The pixel is changed to the 8-bit binary number of the new RGB
color.
1.2.2.3 Recovering the data
The stego tool finds the 8-bit binary number of each pixels RGB color. The LSB of each pixel's 8-bit
binary number is one bit of the hidden data file. Each LSB is then written to an output file.
13
A simplified example with an 8-bit image
1 pixel:
(00 01 10 11)
white red green blue
Insert 0011:
(00 00 11 11)
white white blue blue
As can be seen from the example, with an 8-bit image, the cover image must be carefully selected
since LSB manipulation is not as forgiving because of the color limitations. To hide information in
the LSBs of each byte of a 24-bit image, it is possible to store 3 bits in each pixel.
A simplified example with a 24-bit image
1 pixel:
(00100111 11101001 11001000)
Insert 101:
(00100111 11101000 11001001)
red green blue
LSB insertion works well with gray-scale images as well. It is possible to hide data in the least and
second least significant bits and the human eye would still not be able to discern it.
14
Unfortunately LSB insertion is vulnerable to slight image manipulation such as cropping and com-
pression. For example, converting a GIF or a BMP image, which reconstructs the original message
exactly (lossless compression), to a JPEG format, which does not (lossy compression), and then con-
verting back, can destroy the data in the LSBs.
If NO. of least significant bits increases then the hiding capacity increasesbut image degrades.
1.4.1.4 Images detection
Examine color palette
Size of the image
Differences:
Format
Last modified date
LSB makes use of BMP images, since they use lossless compression. Unfortunately to be
able to hide a secret message inside a BMP file, one would require a very large cover image. Nowa-
days, BMP images of 800 × 600 pixels are not often used on the Internet and might arouse suspicion .
For this reason, LSB steganography has also been developed for use with other image file formats.
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5. Text inside a image
In this techniques we hide secret text data inside a jpeg image .
Figure3 Text data
Figure4 Input image
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Fig 5 out put image
The input image and output image are both looking same but if you open the output image by note pad then you see the secrete data inside the image.
Fig 6 Out put image by notepad
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Fig 7 Covered data 1.jpg 36.1KB stego.jpg 36.3KB stegomessage 39.2KB
1.2.3 Audio steganography
In audio steganography, secret message is embedded into digitized audio signal which result slight
altering of binary sequence of the corresponding audio file. There are several methods are available
for audio steganography. We are going to have a brief introduction on some of them.
1.2.3.1 LSB Coding
Sampling technique followed by Quantization converts analog audio signal to digital binary
sequence. In this technique LSB of binary sequence of each sample of digitized audio file is
replaced with binary equivalent of secret message.
1.2.3.2 Phase Coding
Human Auditory System (HAS) can’t recognize the phase change in audio signal as easy it can
recognize noise in the signal. The phase coding method exploits this fact. This technique encodes the
secret message bits as phase shifts in the phase spectrum of a digital signal, achieving an inaudible
encoding in terms of signal-to- noise ratio.
1.2.4Video Steganography
When information is hidden inside video the program or person hiding the information will usually
use the DCT (Discrete Cosine Transform) method.DCT works by slightly changing the each of the
images in the video, only so much though so it’s isn’t noticeable by the human eye. To be more
precise about how DCT works, DCT alters values of certain parts of the images, it usually rounds
them up. For example if part of an image has a value of 6.667 it will round it up to 7. Steganography
in Videos is similar to that of Steganography in Images, apart from information is hidden in each
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frame of video. When only a small amount of information is hidden inside of video it generally isn’t
noticeable at all, however the more information that is hidden the more noticeable it will become.
1.2.5 Need and applications of steganography
There has been a rapid growth of interest in this subject over the last two years, and for two main
reasons. Firstly, the publishing and broadcasting industries have become interested in techniques for
hiding encrypted copyright marks and serial numbers in digital images, audio recordings, books and
multimedia products; an appreciation of new market opportunities created by digital distribution is
coupled with a fear that digital works could be too easy to copy. Secondly, moves by various
governments to restrict the availability of encryption services have motivated people to study
methods by which private messages can be embedded in seemingly innocuous cover messages.
There are a number of other applications driving interest in the subject of information hiding:
•Military and intelligence agencies require unobtrusive communications. Even if the content is
encrypted, the detection of a signal on a modern battlefield may lead rapidly to an attack on the
signaler. For this reason, military communications use techniques such as spread spectrum
modulation or meteor scatter transmission to make signals hard for the enemy to detect or jam.
•Criminals also place great value on unobtrusive communications. Their preferred technologies
include prepaid mobile phones, mobile phones which have been modified to change their identity
frequently, and hacked corporate switchboards through which calls can be rerouted.
•Law enforcement and counter intelligence agencies are interested in understanding these technologie
s and their weaknesses, so as to detect and trace hidden messages.
•Recent attempts by some governments to limit online free speech and the civilian use of cryptograph
y have spurred people concerned about liberties to develop techniques for anonymous
communications on the net, including anonymous remailers and Web proxies.
•Schemes for digital elections and digital cash make use of anonymous communication techniques.
•Marketers use email forgery techniques to send out huge numbers of unsolicited messages while
avoiding responses from angry users.
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Other applications for steganography include the automatic monitoring of radio advertisements, wher
e it would be convenient to have an automated system to verify that adverts are played as contracted;
indexing of video mail, where we may want to embed comments in the content; and medical safety,
where current image formats such as DICOM separate image data from the text (such as the patient's
name, date and physician), with the result that the link between image and patient occasionally gets
mangled by protocol converters.
2 Literature Review
2.1Text Steganography: A Novel ApproachProposed by-Debnath Bhattacharyya, Poulami Das,Samir Kumar Bandyopadhyay, and Tai-hoon KimAbstract-
A security model is proposed which imposes the concept of secrecy over privacy for text
messages.
This model proposed of combines cryptography and steganography, with extra layer. This newly
introduce extra layer of security changes the format of normal encrypted message and the security
layer follow its encrypted message.
Introduction-
Classical cryptography is one of the ways to secure plain text messages. Along with that at the
time of data transmission, security is also implemented by introducing the concept of
steganography, watermarking, etc. In this types of combined approach, there exits some drawbacks.
In remote networking, at the time of transmission of hidden encrypted text message, if the
eavesdroppers get the track of the hidden text, then they could easily get the encrypted text. Now
breaking of encrypted text message can be achieved by applying some brute force technique. So,
there remains some probability of snooping of information. So, this type of techniques incurs another
level of security which can route the Cryptanalyzer or Steganalyzer in a different direction.
In this work, two new methods namely code_matrix mapping and matrix_pix mapping are
used to employ the above mentioned extra layer of security and in this paper we have considered the
image file format as our covering multimedia object. But, the same technique can be applied for other
multimedia file formats.
Related works-
Least significant bit (LSB) insertion is a common and simple approach to embed information
in a cover object. For images as a covering media, the LSB of a pixel is replaced with an M’s bit. If
20
we choose a 24-bit image as cover, we can store 3 bits in each pixel by modifying the LSBs of R, G
and B array. To the human eye, the resulting stego image will look identical to the cover image.
Hiding data in the features of images is also an important technique which uses the LSB
modification concept. In this method, to hide data in an image the least significant bits (LSB) of each
pixel is modified sequentially in the scan lines across the image in raw image format with the binary
data. The portion, where the secret message is hidden is degraded while the rest remain untouched.
An attacker can easily recover the hidden message.
S. K. Bandyopadhyay, Debnath Bhattacharyya, Swarnendu Mukherjee, Debashis Ganguly,
Poulami Das in 2008 has also proposed a heuristic approach to hide huge amount of data using LSB
steganography technique. In their method, they have first encoded the data and afterwards the
encoded data is hidden behind a cover image by modifying the least significant bits of each pixel of
the cover image. The resultant stego-image was distortion less. Also, they have given much emphasis
on space
complexity of the data hiding technique.
Work-
Using asymmetric key cryptography which means different keys are needed to encrypt and
decrypt the data. Here we have divide the domain of the key selection into different sub domains (a
random prime number, a randomly generated number, decimal value of the pixel (only R) from the
cover picture). In this approach we have given strength on division of the domain together with the
key length.
According to our concept, we encrypt the original text message letter by letter applying a
function which involves certain mathematical operations using corresponding letters and also
numbers from the original image. Then, we use two public keys and one private key for encryption
and decryption. These keys are generated randomly following some constraints
and equations. For encryption and decryption, we have used a mathematical operation called
Multiplicative Modulo in between the text and the generated keys. The used mathematical relation is
given below
C = remainder of (a*b)/p
.
(Say, a, b are any numbers and p be a prime number such that 0 < a, b < p.). This technique
constitutes the first layer of Security in our model.
21
Now, in the next attempt we have used one new method code_matrix mapping. In this
method, the encrypted code is first is broken digit by digit. Next digits are converted into binary
matrices having size DP (Depth of the cover Picture) X x where x gives the resultant code plus 1
where the code is obtained from the encryption procedure of the text. Here, the content of the
matrices are not important and it can have any binary value. This approach incurs second layer of
Security in our model. After that we have used another new method matrix_pix mapping. In this
method the matrices obtained previously are mapped into zone of pixels having area DP X x (in
bytes) where again x represents the same (previously mentioned) and DP represents the depth of the
picture, by using Steganography (Least Significant Bit of the pixel bytes are modified). Here, also
after mapping of each matrix we have left one pixel unchanged after mapping a certain set of
matrices (constituting a word) we have left 2 pixels unchanged. This type of operation implements
third layer of Security in our work.
operation implements third layer of Security in our work. The change in Least Significant Bit in the
value of Red-Green-Blue (pixel) is likely to be undetectable by human eye. Even if the hackers could
predict that a message is hidden inside the image, then they could at most acquire the matrices. These
matrices should be effectively converted to obtain the encrypted data. After this, the encrypted data
needs to be decrypted with the use of the private key to obtain a cipher code which has to be again
decrypted to finally retrieve the original text. So, for the hackers it is very difficult to salvage the data
crossing these Multiple Layers of Security.
Result-
During our implementation phase, we have tested our algorithm for different sets of images as well as
text messages. For each and every normal bitmap images the proposed technique is working fine. We
have also calculated that using a standard 1024 X 768 bitmap image, we can hide approximately
23130 numbers of characters. So, to illustrate our model, we are showing only one satisfactory
experimental result due to the limitation of space.
Cover Image [34748 Bytes Final Image [34748 Bytes]
22
2.2 Digital steganography for information security The application of digital steganography include digital watermarking for copyright protection of
multimedia data, digital signature authentication and validation of electronic documents, digital data
storage, and linkage for binding digitized photographs with personal attribute information, as well
secure communication of multimedia data. Data Mark Technologies(DMT) have developed four
steganography products based on their patent pending algorithms[3,4,5] as follows:
1. Secure Communication(steg comm)
2. Digital Signature Authentication(steg sign)
3. Digital Watermarking(steg mark)
4. Digital Storage and Linkage(steg safe)
1. Secure Communication
StegCommTM is a state-of-the-art digital steganography software package developed by DMT for
confidential multimedia communication. The software allows the user to select a multimedia data file
or "container" for embedding hidden text, audio sequence, video clip, or any form of data file. The
contents of the text message are hashed with those of the container file to produce a key file. The key
file is also known as a “Stegfile”.
Many conventional steganography techniques simply incorporate a combination of cryptography and
steganography. The cryptography operation is used first to scramble the hidden text. For
steganography operation, the scrambled data is then inserted or "hidden" into the least significant bits
(LSB) of the container data. One of the common drawbacks of these techniques is that the container
file has to be of certain size greater than the hidden file. Other limitations include the knowledge
required on the exact location of the hidden text, the limited container data formats, and the export
restriction of using encryption algorithms to certain countries. These difficulties are circumvented by
the use of StegComm™.
1. First, StegCommTM utilises a patent-pending lossless algorithm (the HTTY algorithm) that
does not affect the data integrity of the container file.
2. Second, the program is completely independent of the size of the container file relative to
that of the hidden file.
3. Third, as steganography is a relatively new field, there are currently no export restrictions on
products that incorporate this technology.
23
Another key advantage of the lossless algorithm is the option to select any digital data file from a
webpage on the Internet. As the algorithm does not corrupt or overwrite the container file,
multimedia data posted on any webspage, such as images (JPEG, GIF), video clips (AVI, MPEG) or
audio files (WAV, MIDI), can be selected as the container file. Furthermore, customised container
files, such as the voices and images of the sender captured via video conferencing, can be generated
very easily. Therefore, the probability of knowing which container file used during encoding is
infinitesimally small. It is almost like "finding a needle in a haystack”.
2.3DIGITAL SIGNATURE AUTHENTICATION
StegSignTM is a software product specifically developed by DMT to prevent malicious tampering of
private and confidential documents. These documents include company memos, Emails and letters.
StegSignTM can provide a wide spectrum of applications in the e-commerce sector. Such e-
commerce applications include business transactions between banks and customers, legal document
exchanges between lawyers and clients, and scenarios involving non-repudiation issues. This product
will detect any unwarranted tampering and alert the receiver side immediately. A digital signature
and a multimedia container password are embedded into the confidential document. The digital
signature can be inputted as a handwritten signature or as a personal seal. The container password can
either be a normal text string, an
image, or a binary file.
2.4 Digital signature authentication
StegMarkTM is a digital watermarking software for copyright protection of digital images, music
CDs, DVDs, and other forms of multimedia data. In the case of digital images, the files can come
from a variety of sources, such as the Internet, digital still cameras, and video cameras. Many digital
watermarking techniques in the market embed only a certain number of bits or characters into the
image. However, StegMarkTM can embed either a text or image watermark invisibly into an
"unlabelled" image.
The text watermark can be of many characters, for example, for a colour image of size 512 x 512,
more than a few thousand characters may be embedded.
The image watermark technique of StegMarkTM is currently the only digital watermarking product
available in the market that offers the embedding of a company's logo/trademark into an image. For a
512 x512 image, an image watermark of size up to 128 x 128 can be embedded entirely into the
image, without the loss of image integrity.
How robust a watermark is depends on whether it can survive various "attacks" that include contrast
24
changes, cropping, scratches, and filtering. However, the image integrity of the "labelled" image must
not degrade poorly from an increased level of robustness to these attacks. There are currently many
exaggerating claims that some watermarking techniques can survive all kinds of image manipulation
attacks. However, many of these attacks will destroy the watermark, simply because the labelled
image values with the embedded watermark have now been significantly modified. Obviously,
depending on the watermarking techniques, some attacks can be defended more successful than
others.
StegMarkTM has been tested repeatedly with a number of image attacks that included contrast
stretching (reduction and sharpening), pixel defects, low pass and high pass filtering on the image-in-
image watermarking technique. The image watermark is able to survive most of these attacks.
Watermarking-
Watermarking: is the practice of imperceptibly altering a cover to
embed a message about that cover
Watermarking is closely related to steganography, but there are
differences between the two:
In watermarking the message is related to the cover
Steganography typically relates to covert point-to-point communication
between two parties
Therefore, steganography requires only limited robustness
Watermarking is often used whenever the cover is available to parties
who know the existence of the hidden data and may have an interest in
removing it
Therefore, watermarking has the additional notion of resilience against
attempts to remove the hidden data
25
Watermarks are inseparable from the cover in which they are
embedded. Unlike cryptography, watermarks can protect content
even after they are decoded.
2.4Steganography of plain text and image Bijoy Bandyopadhyay
University of Calcutta, Kolkata, India,
Abstract:
Steganography is the technique of hiding confidential information within a media. The difference
between steganography and cryptography is that in steganography the information is hidden but in
cryptography the output is scrambled so as to draw the attention. Steganalysis is the process to detect
the presence of stegaography.
Keywords:
Steganography,steganalysis, discrete cosine transformation(DCT),Ipv4 header, IP datagram
fragmentation.
Introduction:
The use of modern steganography is to hide information into digital multimedia file and also at
network packet level.
Following elements are required for hiding information into media:
1. The cover media(C) which will hold the hidden information.
2. The secret message(M) which may be plain text, hidden text or any type of data.
3. The stego function(Fe) and its inverse(Fe-1)
4. Inorder to hide or unhide the message an optional stego key(K) or psssword may be used.
The stego function operates over cover media and the message (to be hidden)
along with a stego-key (optionally) to produce a stego media (S).
The schematic of steganographic operation is shown below.
2.5: Digital Watermarking
26
The modern technique of steganography uses the property of media itself to convey a message.
The candidates for the digitally embedding message:-
1. plain text
2. still imagery
3. audio and video
4. IP datagram
Still Imagery of Steganography
This is the most widely used technique for hiding of the secret message. This steganography exploits
weakness of Human Visual System(HVS). Hvs cannot detect variation of luminance of colour
vectors at higher frequency of visual spectrum. A picture can be represented by collection of colour
pixels. Each of these characteristics can be digitally expressed in terms of 0 and 1.
For example: a 24-bit bitmap will have 8 bits, representing each of the three colour values (red,
green, and blue) at each pixel. If we consider just the blue there will be 28 different values of blue.
The difference between 11111111 and 11111110 in the value for blue intensity is likely to be
undetectable by the human eye.(here the 1 from the right hand side is the LSB). Hence,for human
visual system (HVS) then the Least Significant Bit (LSB) can be used for something else other than
colour information.
This technique can be directly applied on digital image in bitmap format as well as for the
compressed image format like JPEG.
Modification of LSB of a cover image in 'bitmap' format .
In this method binary equivalent of the message (to be hidden) is distributed among the LSBs of each
pixel. For example we will try to hide the character ‘A’ into an 8-bit color image.
We are taking eight consecutive pixels from top left corner of the image. The equivalent binary bit
pattern of those pixels may be like this: -
00100111 11101001 11001000 00100111 11001000 11101001
11001000 00100111
Then each bit of binary equivalence of letter 'A' i.e. 01100101 are copied serially (from the left hand
side) to the LSB's of equivalent binary pattern of pixels, resulting the bit pattern will become like
this: -
00100110 11101001 11001001 00100110 11001000 11101001
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11001000 00100111
The only problem with this technique is that it is very vulnerable to attacks such
as image compression and formatting.
Apply of LSB technique during discrete cosine transformation (DCT) [4] on cover image.
The following steps are followed in this case: -
1.The Image is broken into data units each of them consists of 8 x 8 block of pixels.
2.Working from top-left to bottom-right of the cover image, DCT is applied to each pixel of each
data unit.
3.After applying DCT, one DCT Coefficient is generated for each pixel in data unit.
4.Each DCT coefficient is then quantized against a reference quantization table.
5. The LSB of binary equivalent the quantized DCT coefficient can be replaced by a bit from secret
message.
6. Encoding is then applied to each modified quantized DCT coefficient to produce compressed
Stego Image.
2.6OVERVIEW
Steganography comes from the Greek words Steganós (Covered) and Graptos (Writing). The origin
of steganography is biological and physiological. The term “steganography” came into use in 1500’s
after the appearance of Trithemius’ book on the subject “Steganographia”. A short overview in this
field can be divided into three parts and they are Past, Presentand Future .
Past
The word “Steganography” technically means “covered or hidden writing”. Its ancient origins can be
traced back to 440 BC. Although the term steganography was only coined at the end of the 15th
century, the use of steganography dates back several millennia. In ancient times, messages were
hidden on the back of wax writing tables, written on the stomachs of rabbits, or tattooed on the scalp
of slaves. Invisible ink has been in use for centuries—for fun by children and students and for serious
espionage by spies and terrorists . Cryptography became very common place in the middle ages.
Secret writing was employed by the Catholic Church in its various struggles down the ages and by
the major governments of the time. Steganography was normally used in conjunction with
cryptography to further hide secret information .
Present
The majority of today’s steganographic systems uses multimedia objects like image, audio, video etc
as cover media because people often transmit digital pictures over email and other Internet
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communication In modern approach, depending on the nature of cover object, steganography can be
divided into five
Text Steganography
Image Steganography
Audio Steganography
Video Steganography
Protocol Steganography
So, in the modern age so many steganographic techniques have been designed which works with the
above concerned objects. More often in today’s security advancement, we sometimes come across
certain cases in which a combination of Cryptography and Steganography are used to achieve data
privacy over secrecy. Various software tools are also available .
Future
In today’s world, we often listen a popular term “Hacking”. Hacking is nothing but an unauthorized
access of data which can be collected at the time of data transmission. With respect to steganography
this problem is often taken as Steganalysis . Steganalysis is a process in which a steganalyzer cracks
the cover object to get the hidden data. So, whatever be the technique will be developed in future,
degree of security related with that has to be kept in mind. It is hoped that Dual Steganography,
Steganography along with Cryptography may be some of the future solution for this above mentioned
problem.
3.Multi segment steganography techniques
Proposed by Fayik Alnawok and Basem Ahmed
Faculty of Applied Science, Al Aqsa University, Palestine
Code Table
The code table is build up according to the idea of having a random numbers (from 0 to 221),
the number 221 comes from that we have 35 characters, and each
of them have 6 random codes according to the techniques above. After that each
character will be assigned to six random numbers. Now let the sender and receiver share the
password "1234QTR" and the code table, as shown in Table 1.
4.2 Message Hiding
In this stage the sender wants to send the message "MESSAGE". First he should decode the
message into corresponding code for each character by choosing random character from it list
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of code words, let the random numbers be 5, 0, 4, 3, 2, 1, 3. So the
message becomes 92, 174, 113, 111, 21, 167, 192
and the
secret password coding is 142, 69, 170, 217, 117, 65, 80.
The next step starting to search the image from the
byte 142*10; i.e., from byte 1420 about the value 92
let us found it at byte 1500 we changed the value of the
bytes 1497 and 1503 into 1420, or 2/3*1420 or
4/3*1420 these factors have been chosen depends on
that we want the new values closer to the
original value, the next step we start searching
from the byte 690 about the value 174 and we
found it at the byte 800, now we change the value of
the bytes 797 and 803 into 174 and so on for the
reaming characters of the message we are going to
hide according to the next pseudo code .
1. Start message hiding.
2. Code the message by using random (code
word corresponding to each character of the
message).
3. Code the password with the first code word from the list of code word corresponding to each character
4. For i=1 to length(message)
For (j=ith password code * 10 to size of the image)
If (byte(j)==code word of ith character of the message)
Then stop the loop
If(absolute value(byte (j-3)- ¾ * ith character of the message)< byte(j-3) – ith character of the
message) and
(absolute value(byte (j-3)- ¾ * ith character of the message)< byte(j-3) – 4/3 * ith character of the
message)
Then byte (j-3) = ¾ * ith character of the message.
Q
W E R T Y U I O P A S D F G H J K L Z X C V B N M
Space 0 1 2 3 4 5 6 7 8 9
of the password.
Table1. Codes table.
List of Code words
117 168 174 80 65
182 53
177 158 101 203
5 78 34
144 73 42
109 71
140 48
154 195 105 211 47
162 114 142 69
170 217 146 133 147 74
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128 180 82 115 137 218 23 62 72 200 95 120 59 104 167 28 100 37 52 90 209 39 81 165 14 88 79 213 187 132 43 161 148
7 159 55 85
63 156 212 169 143 201 220 84 139 57 21 150 54 56 131
0 33 98 106 25 76 93 117 135 176 199 96 97 99 116 40 175 196 107 122 185
1
66 10 192 11 58 50 149 210 45 173 123 111 13 138
4 118 155 60 75 204 121 94 49 172 26 164 215 110 206 198 197 125 134 214 189 126 221
171 91 12 130 61 153 127 89 41 83 202 113 86 119 46 145 205 166
9 77 188 112 129 179 38 178 87 27 186 24 181 207 20 8
70 193 67
3 190 209 103 183 216 22 35 17 64 184 102 108 208 16 18 19 6
191 32 160 151 194 44 124 92 30 36 157 51 2
68 136 15 152 29
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Else if (absolute value(byte (j-3) – 4/3 * ith character of the message)< byte(j-3) – ith character of the
message) and (absolute value(byte (j-3) – 4/3 * ith character of the message)< byte(j-3) – 3/4 * ith
character of the message)
Then byte (j-3) = 4/3 * ith character of the message.
Else byte (j-3) = ith character of the message.
Do steps b,c and d for the byte (j+3).
5. If the I equal the length (password)
Then i = I mod length (password).
6. End.
My question on this algorithm is –there is no use of specific pos
Ition.
Marking specific byte at specific distance.
To find the specific position
4.CONCLUSION
Although only some of the main steganographic techniques were discussed in this paper, one can see
that there exists a large selection of approaches to hiding information in images. All the major
image file formats have different methods of hiding messages, with different strong and weak
points respectively. Where one technique lacks in payload capacity, the other lacks in robustness.
For example, the patchwork approach has a very high level of robustness against most type of
attacks, but can hide only a very small amount of information. Least significant bit (LSB) in both
BMP and GIF makes up for this, but both approaches result in suspicious files that increase the
probability of detection when in the presence of a warden.
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5 REFERENCES
[1] Bhattacharyya, Poulami Das,Samir Kumar Bandyopadhyay, and Tai-hoon Kim “Text
Steganography: A Novel ApproachProposed Debnath”.
[2] Fayik Alnawok and Basem Ahmed “Multi segment steganography techniques”2007
Faculty of Applied Science, Al Aqsa University, Palestine
[3] Jamil, T., “Steganography: The art of hiding information is plain sight”, IEEE Potentials, 18:01,
1999 .
[4] Moerland, T., “Steganography and Steganalysis”, Leiden Institute of Advanced Computing
Science, www.liacs.nl/home/ tmoerl/privtech.pdf.
[5] Silman, J., “Steganography and Steganalysis: An Overview”, , 2001 .
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