Steganography- A Data Hiding Technique

Abstract

Steganography is the art of hiding information and an effort to conceal the existence of the embedded information. It serves as a better way of securing message than cryptography which only conceals the content of the message not the existence of the message. Original message is being hidden within a carrier such that the changes so occurred in the carrier are not observable. In this paper we will discuss how digital images can be used as a carrier to hide messages. This paper also analyses the performance of some of the steganography tools. Steganography is a useful tool that allows covert transmission of information over an over the communications channel. Combining secret image with the carrier image gives the hidden image. The hidden image is difficult to detect without retrieval. This paper will take an in-depth look at this technology by introducing the reader to various concepts of Steganography, a brief history of Steganography and a look at some of the Steganographic technique.

Full text

International Journal of Computer Applications (0975 – 8887)
Volume 9– No.7, November 2010
19
Steganography- A Data Hiding Technique
Arvind Kumar Km. Pooja
Assistant Professor Vankateshwara institute of computer
Vidya College of engineering, Meerut, India Science and technology, Meerut, India
ABSTRACT
Steganography is the art of hiding information and an effort to
conceal the existence of the embedded information. It serves as a
better way of securing message than cryptography which only
conceals the content of the message not the existence of the message.
Original message is being hidden within a carrier such that the
changes so occurred in the carrier are not observable. In this paper we
will discuss how digital images can be used as a carrier to hide
messages. This paper also analyses the performance of some of the
steganography tools. Steganography is a useful tool that allows covert
transmission of information over an over the communications
channel. Combining secret image with the carrier image gives the
hidden image. The hidden image is difficult to detect without
retrieval.
This paper will take an in-depth look at this technology by
introducing the reader to various concepts of Steganography, a brief
history of Steganography and a look at some of the Steganographic
technique.
KEYWORDS
Steganography, Steganalysis, Digital watermarking, Stego key, Stego
image and Cryptography.
1. INTRODUCTION
Internet users frequently need to store, send, or receive private
information. The most common way to do this is to transform the data
into a different form. The resulting data can be understood only by
those who know how to return it to its original form. This method of
protecting information is known as encryption. A major drawback to
encryption is that the existence of data is not hidden. Data that has
been encrypted, although unreadable, still exists as data. If given
enough time, someone could eventually unencrypt the data. A
solution to this problem is steganography. The ancient art of hiding
messages so that they are not detectable. No substitution or
permutation was used. The hidden message is plain, but unsuspecting
to the reader. Steganography's intent is to hide the existence of the
message, while cryptography scrambles a message so that it cannot be
understood.
Before the invention of digital means, traditional methods were being
used for sending or receiving messages. Before phones, before mail
messages were sent on foot. For the messages where privacy was of
prime concern, the ways of implementing security were following:
1. Choosing the messenger capable of delivering the message
securely.
2. Write the message using such notations that actual meaning of the
message was concealed.
3. Hide the message such that even its presence can’t be predicted.
In steganography, the possible cover carriers are innocent looking
carriers (images, audio, video, text, or some other digitally
representative code) which will hold the hidden information. A
message is the information hidden and may be plaintext, cipher text,
images, or anything that can be embedded into a bit stream. Together
the cover carrier and the embedded message create a stego-carrier.
Hiding information may require a stego key which is additional secret
information, such as a password, required for embedding the
information. For example, when a secret message is hidden within a
cover image, the resulting product is a stego-image.
A possible formula of the process may be represented as: cover
medium + embedded message + stego key = stego-medium
Figure 1.1 Graphical Version of the Steganographic System
fE : steganographic function "embedding"
fE-1 : steganographic function "extracting"
cover: cover data in which emb will be hidden
emb: message to be hidden
stego: cover data with the hidden message
The advantage of steganography is that it can be used to secretly
transmit messages without the fact of the transmission being
discovered. Often, using encryption might identify the sender or
receiver as somebody with something to hide. For example, the
picture of our cat could conceal the plans for our company's latest
technical innovation.
2. HISTORY OF STEGANOGRAPHY
It is believed that steganography was first practiced during the Golden
Age in Greece. An ancient Greek record describes the practice of
melting wax off wax tablets used for writing messages and then
inscribing a message in the underlying wood. The wax was then
reapplied to the wood, giving the appearance of a new, unused tablet.
The resulting tablets could be innocently transported without anyone
suspecting the presence of a message beneath the wax.
An ancient Greek record describes the practice of melting wax off
wax tablets used for writing messages and then inscribing a message
in the underlying wood. The wax was then reapplied to the wood,

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Volume 9– No.7, November 2010
20
giving the appearance of a new, unused tablet. The resulting tablets
could be innocently transported without anyone suspecting the
presence of a message beneath the wax.
Later on Germans developed microdot technology which FBI
Director J. Edgar Hoover referred to as "the enemy's masterpiece of
espionage. Microdots are photographs the size of a printed period
having the clarity of standard-sized typewritten pages. The first
microdots were discovered masquerading as a period on a typed
envelope carried by a German agent in 1941. The message was not
hidden, nor encrypted. It was just so small as to not draw attention to
itself. Besides being so small, microdots permitted the transmission of
large amounts of data including drawings and photographs.
Another common form of invisible writing is through the use of
Invisible inks. Such inks were used with much success as recently as
WW-II. An innocent letter may contain a very different message
written between the lines. Early in WW-II steganographic technology
consisted almost exclusively of invisible inks. Common sources for
invisible inks are milk, vinegar, fruit juices and urine. All of these
darken when heated.
3. USES OF STEGANOGRAPHY
1. Steganography can be a solution which makes it possible to send
news and information without being censored and without the fear of
the messages being intercepted and traced back to us.
2. It is also possible to simply use steganography to store information
on a location. For example, several information sources like our
private banking information, some military secrets, can be stored in a
cover source. When we are required to unhide the secret information
in our cover source, we can easily reveal our banking data and it will
be impossible to prove the existence of the military secrets inside.
3. Steganography can also be used to implement watermarking.
Although the concept of watermarking is not necessarily
steganography, there are several steganographic techniques that are
being used to store watermarks in data. The main difference is on
intent, while the purpose of steganography is hiding information,
watermarking is merely extending the cover source with extra
information. Since people will not accept noticeable changes in
images, audio or video files because of a watermark, steganographic
methods can be used to hide this.
Figure3.1 Steganography Types
4. E-commerce allows for an interesting use of steganography. In
current e-commerce transactions, most users are protected by a
username and password, with no real method of verifying that the
user is the actual card holder. Biometric finger print scanning,
combined with unique session IDs embedded into the fingerprint
images via steganography, allow for a very secure option to open e-
commerce transaction verification.
5. Paired with existing communication methods, steganography can
be used to carry out hidden exchanges. Governments are interested in
two types of hidden communications: those that support national
security and those that do not. Digital steganography provides vast
potential for both types. Businesses may have similar concerns
regarding trade secrets or new product information.
6. The transportation of sensitive data is another key use of
steganography. A potential problem with cryptography is that
eavesdroppers know they have an encrypted message when they see
one. Steganography allows to transport of sensitive data past
eavesdroppers without them knowing any sensitive data has passed
them. The idea of using steganography in data transportation can be
applied to just about any data transportation method, from E-Mail to
images on Internet websites.
Figure 3.2 Steganography on the Internet
4. STEGANOGRAPHY AND
CRYPTOGRAPHY
4.1 Comparison of Steganography and
Cryptography
Steganography and cryptography are closely related. Cryptography
scrambles messages so it can’t be understood. Steganography on the
other hand, hide the message so there is no knowledge of the
existence of the message. With cryptography, comparison is made
between portions of the plaintext and portions of the cipher text. In
steganography, comparisons may be made between the cover-media,
the stego-media, and possible portions of the message. The end result
in cryptography is the cipher text, while the end result in
steganography is the stego-media. The message in steganography may
or may not be encrypted. If it is encrypted, then a cryptanalysis
technique is applied to extract the message.

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4.2 Combination of Steganography and
Cryptography
Those who seek the ultimate in private communication can combine
encryption and steganography. Encrypted data is more difficult to
differentiate from naturally occurring phenomena than plain text is in
the carrier medium. There are several tools by which we can encrypt
data before hiding it in the chosen medium.
In some situations, sending an encrypted message will across
suspicion while an invisible message will not do so. Both methods
can be combined to produce better protection of the message. In case,
when the steganography fails and the message can be detected, it is
still of no use as it is encrypted using cryptography techniques.
5. STEGANALYSIS
Steganalysis is "the process of detecting steganography by looking at
variances between bit patterns and unusually large file sizes”. It is the
art of discovering and rendering useless covert messages. The goal of
steganalysis is to identify suspected information streams, determine
whether or not they have hidden messages encoded into them, and, if
possible, recover the hidden information. Unlike cryptanalysis, where
it is evident that intercepted encrypted data contains a message.
Figure 1. A Graphical Version of the Steganographic System
Steganalysis generally starts with several suspect information streams
but uncertainty whether any of these contain hidden message. The
steganalyst starts by reducing the set of suspect information streams
to a subset of most likely altered information streams. This is usually
done with statistical analysis using advanced statistics techniques.
6. STEGANALYSIS TECHNIQUES
Hiding information within an electronic medium cause alteration of
the medium properties that can result in some form of degradation or
unusual characteristics.
6.1. Unusual patterns
Unusual patterns in a stego image are suspicious. For example, there
are some disk analysis utilities that can filter hidden information in
unused partitions in storage devices. Filters can also be used to
identify TCP/IP packets that contain hidden or invalid
information in the packet headers. TCP/IP packets used to
transport information across the Internet have unused or
reserved space in the packet headers.
6.2. Visual detection
Analyzing repetitive patterns may reveal the identification of a
steganography tool or hidden information. To inspect these patterns
an approach is to compare the original cover image with the stego
image and note visible differences. This is called a known-carrier
attack. By comparing numerous images it is possible that patterns
emerge as signatures to a steganography tool. Another visual clue to
the presence of hidden information is padding or cropping of an
image. With some stego tools if an image does not fit into a fixed size
it is cropped or padded with black spaces. There may also be a
difference in the file size between the stego-image and the cover
image. Another indicator is a large increase or decrease in the number
of unique colors, or colors in a palette which increase incrementally
rather than randomly.
6.3. Tools to detect Steganography
The disabling or removal of hidden information in images is
dependent on the image processing techniques. For example, with
LSB methods of inserting data, simply compressing the image using
lossy compression is enough to disable or remove the hidden
message. There are several available steganographic detection tools
such as Encase by Guidance Software Inc., ILook Investigator by
Electronic Crimes Program, Washington DC, various MD5 hashing
utilities, etc.
7. IMPLEMENTATION AND RESULTS
All of the approaches to steganography have one thing in common
that they hide the secret message in the physical object which is sent.
The following figure shows the steganography process of the cover
image being passed into the embedding function with the message to
encode resulting in a steganographic image containing the hidden
message. A key is often used to protect the hidden message. This key
is usually a password, so this key is also used to encrypt and decrypt
the message before and after the embedding.
Secrets can be hidden inside all sorts of cover information: text,
images, audio, video and more. However, there are tools available to
store secrets inside almost any type of cover source. The most
important property of a cover source is the amount of data that can be
stored inside it, without changing the noticeable properties of the
cover.
Figure 5.1 Steganography Procedure

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In this phase, here we are going to implement steganography
technique on the following images.
Figure 5.2 Cover Image
Figure 5.3 Secret Image
The figure 5.2 is our Cover Image and Figure 5.3 is our Secret Image.
After applying this technique on it we get the following image. This
will be known as Stego Image.
Figure 5.4 Stego Image
After implementation of this technique if we take a look on the
histogram of both the images cover image and stego image
respectively we will find both are very different from each other. The
following figures show the histogram of cover image and stego
image.
Figure 5.5 Histogram of Cover Image
Figure 5.6 Histogram of Stego Image
The above two Figure 5.5 shows the histogram of our Cover Image
and Figure 5.6 shows the histogram of Stego Image. Both the images
are different from each other.
8. STEGANOGRAPHY SOFTWARE APPLICATION
8.1 Digital Watermarking
Digital watermarking is the process of embedding information into a
digital signal in a way that is difficult to remove. The signal may be
audio, pictures or video, for example. If the signal is copied, then the
information is also carried in the copy. A signal may carry several
different watermarks at the same time.
8.1.1 Visible Watermarking
In this, the information is visible in the picture or video. Typically, the
information is text or a logo which identifies the owner of the media.
When a television broadcaster adds its logo to the corner of
transmitted video, this is also a visible watermark.
8.1.2 Invisible Watermarking
In this, information is added as digital data to audio, picture or video,
but it cannot be perceived as such (although it may be possible to
detect that some amount of information is hidden). The watermark
may be intended for widespread use and is thus made easy to retrieve
or it may be a form of Steganography, where a party communicates a
secret message embedded in the digital signal. In either case, as in

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visible watermarking, the objective is to attach ownership or other
descriptive information to the signal in a way that is difficult to
remove. It is also possible to use hidden embedded information as a
means of covert communication between individuals.
Digital Watermarking can be used for a wide range of applications
such as: Copyright protection Source Tracking (Different recipients
get differently watermarked content). The numbers of possible
applications for digital watermarking technologies are increasing
rapidly. For example, in the field of data security, watermarks may be
used for certification, authentication, and conditional access.
Certification is an important issue for official documents, such as
identity cards or passports. Digital watermarks are created by
converting copyright information into apparently random digital
"noise" using an algorithm that is imperceptible to all but special
watermark reading software. So while a JPEG file that is read by a
Web browser may display a pretty picture, that same file will display
the copyright when read by the watermark software.
9. CONCLUSION AND FUTURE SCOPE
Steganography transmits secrets through apparently innocuous covers
in an effort to conceal the existence of a secret. Digital image
steganography and its derivatives are growing in use and application.
In areas where cryptography and strong encryption are being
outlawed, citizens are looking at steganography to circumvent such
policies and pass messages covertly. As with the other great
innovations of the digital age: the battle between cryptographers and
cryptanalysis, security experts and hackers, record companies and
pirates, steganography and Steganalysis will continually develop new
techniques to counter each other.
In the near future, the most important use of steganographic
techniques will probably be lying in the field of digital watermarking.
Content providers are eager to protect their copyrighted works against
illegal distribution and digital watermarks provide a way of tracking
the owners of these materials. Steganography might also become
limited under laws, since governments already claimed that criminals
use these techniques to communicate.
The possible use of steganography technique is as following:
Hiding data on the network in case of a breach.
Peer-to-peer private communications.
Posting secret communications on the Web to avoid
transmission.
Embedding corrective audio or image data in case corrosion
occurs from a poor connection or transmission.
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