ABSTRACT
We propose a new method for strengthening the security of information through a combination of signal
processing, cryptography and steganography. Cryptography provides the security by concealing the contents and steganography
provides security by concealing existence of information being communicated. Signal processing adds additional security by
compressing and transforming the information. The proposed method, viz. Steganography Based Information Protection Method
(SBIPM), consists of scanning, coding, encryption, reshaping, cover processing and embedding steps.
We then turn to data-hiding in images. Steganography in images has truly come of age with the invention of fast,
powerful computers. Software is readily available off the Internet for any user to hide data inside images. These softwares are
designed to fight illegal distribution of image documents by stamping some recognisable feature into the image.The most popular
technique is Least Significant Bit insertion, which we will look at. Also, we look at more complex methods such as masking and
filtering, and algorithms and transformations, which offer the most robustness to attack, such as the Patchwork method which
exploits the human eye's weakness to luminance variation.
We will take a brief look at steganalysis, the science of detecting hidden messages and destroying them. We conclude
by finding that steganography offers great potential for securing of data copyright, and detection of infringers. Soon, through
steganography,personal messages,files, all artistic creations, pictures, and songs can be protected from piracy.
1. INTRODUCTION
Now a days, various modes of communication like LAN, WAN and INTERNET are widely used for communicating
information from one place to another around the globe. Such communication networks are open which any one can access easily.
They are regularly monitored and an intercepted.
Steganography, from the Greek, means covered, or secret writing, and is a long-practised form of hiding information.
Although related to cryptography, they are not the same. Steganography's intent is to hide the existence of the message, while
cryptography scrambles a message so that it cannot be understood. More precisely,
'The goal of steganography is to hide messages inside other harmless messages in a way that does not allow any enemy
to even detect that there is a second secret message present."
Steganography includes a vast array of techniques for hiding messages in a variety of media. Among these methods are
invisible inks, microdots, digital signatures, covert channels and spread-spectrum communications. A message is embedded in a
cover media in an invisible manner so that one could not suspect about its existence.
In this paper we present a substitution based information protection method where we combine cryptographic,
steganographic and signal processing concepts together for achieving security. The method is known as Steganography Based
Information Protection method. In this method we substitute the information bit in randomly selected pixels at random places
within LSB region.
2. STEGANOGRAPHY TECHNIQUE
Steganography is the art and science of communicating in a way which hides the the existence of the secret message
communication. It aims to hide information /covered writing. Information to be protected is hidden in another data known as
cover or carrier. Data containing hidden message are called as Steganos or Stegos. Steganos look like cover data and it is difficult
to differentiate between them. Steganography based communication over easily accessible platforms to prevent leakage of
information.
2.1 Kerck Off Principle:
In cryptography, this principle states that "the security of the system has to be based on the assumption that the enemy
has full knowledge of the design and implementation details of the steganographic system". The only missing information for the
enemy is a short, easily exchangeable random number sequence, the secret key.
3. STEGANOGRAPHY METHODS;
According to modification in covers, the methods can be categorized as
❖
Substitution
❖
Transform domain
❖
Spread spectrum
❖
Statistical
❖
Distortion
❖
Cover generation
3.1 Substitution Method:
It is commonly used simple method in which we can put information bits in LSB sequentially at fixed place,
randomly at fixed place or randomly at random places in cover pixels. The message to be protected passes through scanning,
coding, encryption process to form an embedded message.
Scanning, coding, encryption steps make the information unintelligible so that one cannot extract plain message.
Embedding make the message invisible so that one cannot detect it.
Reshaping spreads the message so that embedded message can be detected from distorted steganos by authorized
receivers.
Cover processing makes detection of embedded message more difficult since the distortion is either due to noise
addition or due to message embedding .
This would increases the robustness and security. Many attacks on such steganographic systems are suggested. Some
attacks that can be applied are given below:
❖
Stego-Only Attack
❖
Message-Stego Attack
❖
Cover-Stego Attack
❖
Message-Cover-Stego Attack
3.2 Proposed Method:
The framework of proposed Steganography Based Information Protection method is shown in Fig 1. Its description is presented
in the following steps. FRAME WORK OF SBIPM
STEGANOGRAPHY
MESSAGE
CRYPTO
KEYS
-
CRYPTO PART
SCANNING
EN CRYPTION
CODING
RESHAPING
COVER
EMBEDDING
' ---------------- * ---------------------
STEGOPART
STEGO KEYS
COVER IMAGE
STEGO IMAGE
3.3 Visual Perception:
For any steganography based secure system, the perception of steganos should be as cover image
itself so that one cannot differentiate them and detect the existence of embedded message.
3.4 Difference Analysis:
The "difference-images"obtained by taking the difference between cover, processed cover and stego images are not
visible. For making the difference visible in "difference-images" for visual interpretation, we first increase differences by
multiplication of weight factor and then revert the values to get the strengthened
STEGANOGRAPHY
"difference-images".From analysis of these "difference-images ", on could not say that the changes are either due to cover
processing or message embedding and hence we can say that the method is safe from known cover-stego attack.
3.5 Distortion Analysis:
Distortion analysis of stego images is carried out by studying distortion / similarity messages statistically. There are
many methods for measuring distortion that can be used for distortion analysis. Distortion between two different images is
measured by considering Mean Square Error (MSE), Mean Absolute Error (MAE) or Histogram Similarity (HS).
3.6 Depth Vs Distortion Analysis:
Distortion occurred in different steganos is required by varying the depth of hiding for embedding information in
cover image. The relation between depth of hiding used and distortion occurred in the stego images is shown in Fig. that depth of
hiding within some LSB region is most suitable for message embedding as the distortion is very small in this region. As the
depth of hiding increases beyond preferable region, the distortion becomes noticeable and unsuitable for message hiding.
DEPTH OF HIDING (D) --------------- ►
3.7 Steganography in Images:
DISTORTION (MAE)
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STEGANOGRAPHY
In this section we deal with data encoding in still digital images. In essence, image steganography is about exploiting
the limited powers of the human visual system (HVS). Within reason, any plain text, cipher text, other images, or anything
that can be embedded in a bit stream can be hidden in an image. When embedding data, it is important to remember the
following restrictions and features:
STEGANOGRAPHY ______________________________________ ,
______________________________________
The cover data should not be significantly degraded by the embedded data, and
the embedded data should be as imperceptible as possible. (This does not mean the
embedded data needs to be invisible; it is possible for the data to be hidden while it
remains in plain sight.)
The embedded data should be directly encoded into the media, rather than into a
header or wrapper, to maintain data consistency across formats.
The embedded data should be as immune as possible to modifications from
intelligent attacks or anticipated manipulations such as filtering and resampling.
Some distortion or degradation of the embedded data can be expected when the cover
data is modified. To minimise this, error correcting codes should be used.
The embedded data should be self-clocking or arbitrarily re-entrant. This ensures
that the embedded data can still be extracted when only portions of the cover data is
available. For example, if only a part of image is available, the embedded data should
still be recoverable.
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STEGANOGRAPHY
4. STEGANOGRAPHY DIAGRAMAT1C FLOW
Information to be
hidden
Hidden document
Sitego tool J
Stego tool
Law enforcemed intercept
User can get the hidden information using
but doe! know that
password
document.
4.1 Images:
To a computer, an image is an
array of numbers that represent light intensities at various points, or pixels. These pixels make up the image's raster data. An
image size of 640 by 480 pixels, utilizing 256 colors (8 bits per pixel) is fairly common. Such an image would contain around
300 kilobits of data.
Digital images are typically stored in either 24-bit or 8-bit per pixel fdes. 24-bit images are sometimes known as
true colour images. Obviously, a 24-bit image provides more space for hiding information; however, 24-bit images are
generally large
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STEGANOGRAPHY
and not that common. A 24-bit image 1024 pixels wide by 768 pixels high would have a size in excess of 2 megabytes. As such,
large files would attract attention were they to be transmitted across a network or the Internet. Image compression is desirable.
However, compression brings with it other problems, that shall be explained shortly.
Alternatively, 8-bit colour images can be used to hide information. In 8-bit colour images, (such as GIF files),
each pixel is represented as a single byte. Each pixel merely points to a colour index table, or palette, with 256 possible colours.
The pixel's value, then, is between 0 and 255. The image software merely needs to paint the indicated colour on the screen at the
selected pixel position.
If using an 8-bit image as the cover-image, many steganography experts recommend using images featuring 256
shades of gray as the palette, for reasons that will become apparent. Grey-scale images are preferred because the shades change
very gradually between palette entries. This increases the image's ability to hide information.
When dealing with 8-bit images, the steganographer will need to consider the image as well as the palette.
Obviously, an image with large areas of solid color is a poor choice, as variances created by embedded data might be noticeable.
Once a suitable cover image has been selected, an image encoding technique needs to be chosen.
4.2 Image Compression:
Image compression offers a solution to large image files. Two kinds of image compression are lossless and
lossy compression. Both methods save storage space but have differing effects on any uncompressed hidden data in the image.
Lossy compression, as typified by JPEG (Joint Photographic Experts Group) format files, offers high
compression, but may not maintain the original image's integrity. This can impact negatively on any hidden data in the image.
This is due to the lossy compression algorithm, which may "lose" unnecessary image data, providing a close approximation to
high-quality digital images, but not an exact duplicate. Hence, the term" Tossy" compression. Lossy compression is frequently
used on true-colour images, as it offers high compression rates.
Lossless compression maintains the original image data exactly; hence it is preferred when the original
information must remain intact. It is thus more favoured
STEGANOGRAPHY
by steganographic techniques. Unfortunately, lossless compression does not offer such high compression rates as lossy
compression. Typical examples of lossless compression formats are Compuserve's GIF (Graphics Interchange Format) and
Microsoft's BMP (Bitmap) format.
4.3 Image Encoding Techniques:
Information can be hidden many different ways in images. Straight message insertion can be done, which
will simply encode every bit of information in the image. More complex encoding can be done to embed the message only in
" n o i s y " areas of the image that will attract less attention. The message may also be scattered randomly throughout the cover
image.The most common approaches to information hiding in images are:
❖
Least significant bit (LSB) insertion ♦> Masking and
filtering techniques
❖
Algorithms and transformations
Each of these can be applied to various images, with varying degrees of success. Each of them suffers to
varying degrees from operations performed on images, such as cropping, or resolution decrementing, or decreases in the colour
depth.
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4.4 Least Significant Bit Insertion:
One of the most common techniques used in steganography today is called least significant bit (LSB) insertion.
This method is exactly what it sounds like; the least significant bits of the cover-image are altered so that they form the
embedded information. The following example shows how the letter A can be hidden in the first eight bytes of three pixels in a
24-bit image.
Pixels: (00100111 11101001 11001000)
(00100111 11001000 11101001) (11001000
00100111 11101001)
A:
10000001
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STEGANOGRAPHY
Result: (00100111 11101000 11001000)
(00100110 11001000 11101000) (11001000
00100111 11101001)
The three underlined bits are the only three bits that were actually altered. LSB insertion requires on average that only
half the bits in an image be changed. Since the 8-bit letter A only requires eight bytes to hide it in, the ninth byte of the three
pixels can be used to hide the next character of the hidden message.
A slight variation of this technique allows for embedding the message in two or more of the least significant bits per
byte. This increases the hidden information capacity of the cover-object, but the cover-object degrades more statistically, and it is
more detectable. Other variations on this technique include ensuring that statistical changes in the image do not occur. Some
intelligent software also checks for areas that are made up of one solid color. Changes in these pixels are then avoided because
slight changes would cause noticeable variations in the area.
4.5 Advantages Of LSB Insertion:
Major advantage of the LSB algorithm is it is quick and easy. There has also been steganography software
developed which work around LSB color alterations via palette manipulation.
LSB insertion also works well with gray-scale images. A slight variation of this technique allows for embedding the
message in two or more of the least significant bits per byte. This increases the hidden information capacity.
4.6 Masking And Filtering :
Masking and filtering techniques hide information by marking an image in a manner similar to paper
watermarks. Because watermarking techniques are more integrated into the image, they may be applied without fear of image
destruction from lossy compression. By covering, or masking a faint but perceptible signal with another to make the first non perceptible, we exploit the fact that the human visual system cannot detect slight changes in certain temporal domains of the
image.
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STEGANOGRAPHY
Technically, watermarking is not a steganographic form. Strictly, steganography conceals data in the image;
watermarking extends the image information and becomes an attribute of the cover image, providing license, ownership or
copyright details.
Masking techniques are more suitable for use in lossy JPEG images than LSB insertion because of their relative
immunity to image operations such as compression and cropping.
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STEGANOGRAPHY
5. Algorithms and transformations
Because they are high quality colour images with good compression, it is desirable to use JPEG images across
networks such as the Internet. Indeed, JPEG images are becoming abundant on the Internet.
JPEG images use the discrete cosine transform (DCT) to achieve compression. DCT is a lossy compression
transform, because the cosine values cannot be calculated precisely, and rounding errors may be introduced. Variances between
the original data and the recovered data depends on the values and methods used the calculate the DCT.
Images can also be processed using fast Fourier transformation and wavelet transformation. Other properties such
as luminance can also be utilised. The HVS has a very low sensitivity to small changes in luminance, being able to discern
changes of no less than one part in thirty for random patterns. This figure goes up to one part in 240 for uniform regions of an
image.
Modern steganographic systems use spread-spectrum communications to transmit a narrowband signal over a much
larger bandwidth so that the spectral density of the signal in the channel looks like noise.
The two different spread-spectrum techniques these tools employ are called direct-sequence and frequency
hopping. The former hides information by phase-modulating the data signal (carrier) with a pseudorandom number sequence that
both the sender and the receiver know. The latter divides the available bandwidth into multiple channels and hops between these
channels (also triggered by a pseudorandom number sequence).
The Patchwork method is based on a pseudorandom, statistical process that takes advantage of the human
weaknesses to luminance variation. Using redundant pattern encoding to repeatedly scatter hidden information throughout
the cover image, like a patchwork, Patchwork can hide a reasonably small message many times in a image. In the Patchwork
method, n pairs of image points (a,b) are randomly chosen. The brightness of a is decreased by one and the brightness of b is
increased by one. For a
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STEGANOGRAPHY
labeled image, the expected value of the sum of the differences of the n pairs of points is then 2n. Bender shows that after JPEG
compression, with the quality factor set to 75, the message can still be decoded with an 85 .
This algorithm is more robust to image processing such as cropping and rotating, but at the cost of message
size. Techniques such as Patchwork are ideal for watermarking of images. Even if the image is cropped, there is a good
probability that the watermark will still be readable.
Other techniques encrypt and scatter the hidden throughout the image in some pre-determined manner. It is
assumed that even if the message bits are extracted, they will be useless without the algorithm and stego-key to decode them.
Although such techniques do help protect against hidden message extraction, they are not immune to destruction of the hidden
message through image manipulation.
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STEGANOGRAPHY
6. SYSTEM DESIGN:
These are the steps followed in image hiding while transmission and de noising after receiving:
1.
Get a cover image (publicly accessible material)
2.
Take the information to be hidden (message or image)
3.
Combine cover image with the information to be hidden(we follow LSB algorithm for this)
4.
While transmission it will be corrupted by noise
5.
Use any of the fdtering methods, ex: wiener filtering for de noising in wavelet domain
6.
Here fdter is employed in order to remove the noise
7.
During extraction a password check is provided
8.
If password is matched then extraction of hidden information.
7. SECURITY:
A method, SBIPM, for providing the security of our important information is based on the techniques of signal
processing, cryptography, and steganography. The security of information has been strengthened by applying scanning, coding,
encryption, cover processing and embedding techniques in the method. Reshaping step of the method provides robustness for
detecting message correctly in such situation when stego image is distorted. The method developed is safe from various attacks.
Simulation and steganalysis results shown in this paper shows that one will not be able to distinguish between cover and stego
images.
Thus we conclude that the strength of security achieved is very high and unauthorized receiver will not be able to get
back the original message using exhaustive without the knowledge of key parameters.
Digital Steganography is interesting field and growing rapidly for information hiding in the area of information
security.lt has a vital role in defence as well as civil applications. In future we will more of secure systems based on this
technology. Several methods for hiding data in, images were described, with appropriate introductions to the environments of
each medium, as well as the strengths and weaknesses of each method.The key algorithm for designing the steganography
system has been dealt. Most data-hiding systems take advantage of human perceptual weaknesses, but have weaknesses of their
own. We conclude that for now, it seems that no system of data-hiding is totally immune to attack.
However, steganography has its place in security. Though it cannot replace cryptography totally, it is intended to
supplement it. Its application in watermarking and fingerprinting, for use in detection of unauthorised, illegally copied material,
is continually being realised and developed.
8.FUTURE SCOPE
In this report many relevant issues were presented, from a technical point of view. However, little has been done
to motivate these studies. A more detailed investigation of applications, and a comparison with current techniques in
steganography would have been interesting. For example, a thorough evaluation of the advantages natural language-based
techniques can offer over image-based techniques could have offered valuable insights.
An important contribution of this project to natural language steganography is the linguistic sophistication of the
model for word-substitution put forward. The lexical models employed in current substitution-based systems were often
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STEGANOGRAPHY
criticised and their inadequate behavior usually described with respect to language theory. These phenomena could have been
demonstrated by example, showing texts and inadequate replacements carried out by current stegosystems. A more detailed
analysis of how common these critical situations really are in typical text could have given clues for the construction of such
systems, to decide whether the additional complexity introduced by statistical word-sense disambiguation is worth the effort.
Other linguistic models have been studied, in addition to the lexical ones, and put in relation to each other, and to
their use for steganographic purposes. The steganographic aspects were then covered by information-theoretic models. However,
little has been done to justify this choice. It might have been fruitful to present other characterizations of steganography and to
compare their suitability to natural language steganography.
A central part of the problem motivating this report was that there are no models formalizing the design and analysis
of natural language stegosystems. Although the present report somewhat improves the situation, by providing a systematic
investigation of the topic, there is still no system to build upon for making formal claims about security or robustness in the
natural language scenario.
9. CONCLUSION:
Several methods for hiding data in, images were described, with appropriate introductions to the environments of
each medium, as well as the strengths and weaknesses of each method.The key algorithm for designing the steganography
system has been dealt. Most data-hiding systems take advantage of human perceptual weaknesses, but have weaknesses of their
own. We conclude that for now, it seems that no system of data-hiding is totally immune to attack.
However, steganography has its place in security. Though it cannot replace cryptography totally, it is intended to
supplement it. Its application in watermarking and fingerprinting, for use in detection of unauthorised, illegally copied material,
is continually being realised and developed.
Also, in places where standard cryptography and encryption is outlawed, steganography can be used for covert data
transmission. Steganography can be used along with cryptography to make an highly secure data high way.Formerly just an
interest of the military, Steganography is now gaining popularity among the masses. Soon, any computer user will be able to put
his own watermark on his artistic creations.
Thus we conclude that the strength of security achieved is very high and unauthorized receiver will not be able to get
back the original message using exhaustive without the knowledge of key parameters.
Digital Steganography is interesting field and growing rapidly for information hiding in the area of information
security.lt has a vital role in defence as well as civil applications.
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STEGANOGRAPHY
10. REFERENCE:
l.M.Kuhn.
WWW:Http://wwwjjtcxom/Steganography/steglist.htm,
1995.
Private Site, Hamburg. Germany
2.N.F.Johnson. Steganography.
WWW:http://\vww.jjtc.com/stegdoc/. George Mason University
CONTENTS
1 . I N T R O D U C T I O N ............................................................................................................................ 1
2 . S T E G A N O G R A P H Y T E C H N I Q U E S .......................................................................................2
2 . 1 K E R C K O F F P R I N C I P L E ................................................................................................2
3 . S T E G A N O G R A P H Y M E T H O D S ............................................................................................... 3
3.1
S U B S T I T U T I O N M E T H O D ........................................................................................3
3.2
P R O P O S E D M E T H O D ..................................................................................................... 4
3.3
V I S U A L P E R C E P T I O N .................................................................................................. 4
3.4
D I F F E R E N C E A N A L Y S I S ............................................................................................4
3 . 5 D E P T H V S D I S T O R T I O N A N A L Y S I S ................................................................... 5
3 . 6 S T E G A N O G R A P H Y I N I M A G E S .............................................................................. 7
4. STEGANOGRAPHY
D I A G R A M A T I C F L O W ..................................................................................................... 7
4 . 1 I M A G E C O M P R E S S I O N .................................................................................................................8
4.2IMAGE ENCODING
T E C H N I Q U E S ........................................................................................................................... 9
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4.3 LEAST SIGNIFICANT BIT
I N S E R T I O N .............................................................................................................................. 1 0
4 . 4 M A S K I N G A N D F I L T E R I N G ........................................................................................................ 1 0
5 . A L G O R I T H M S A N D T R A N S F O R M A T I O N S ....................................................................... 1 2
6 . S Y S T E M D E S I G N ...................................................................................................................................... 1 4
7 . S E C U R I T Y ...................................................................................................................................................... 1 5
8 . F U T U R E S C O P E ......................................................................................................................................... 1 6
9 . C O N C L U S I O N .......................................................................................................................................... 1 7
1 0 . R E F E R E N C E ........................................................................................................................................... 1 8
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