Ramakrishna Mathe et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol.

3 (3) , 2012,4251 - 4255

Securing Information: Cryptography and

Steganography
1
Ramakrishna Mathe 2 Veera RaghavaRao Atukuri 3 Dr. Srinivasa Kumar Devireddy
12
Department of Computer Science and Engineering
Malineni Lakshmaiah Women’s Engineering College, Guntur (A.P), INDIA.
3
Prinicpal, Nalanda Institute of Engineering and Technology,
Sattenapally, GUNTUR

Abstract:Today’s dynamic and information rich environment, network communication, so only the receiver who has the
information systems have become vital for any organization to secret key can read the secret messages which might be
survive. With the increase in the dependence of the organization on
the information system, there exists an opportunity for the
documents, images or other forms of data.
competitive organizations and disruptive forces to gain access to other Cryptography and steganography also contribute to
organizations information system. This hostile environment makes
information systems security issues critical to an organization.
Computer Science, particularly, in the techniques used in
Current information security literature either focuses on anecdotal computer and network security for access control and
information by describing the information security attacks taking information confidentiality. They are also used in many
place in the world or it comprises of the technical literature describing applications encountered in everyday life. Despite the
the types of security threats and the possible security systems. Two of differences between Cryptography and Steganography
the best ways to provide security is Cryptography and Steganography.
Cryptography and Steganography are cousins in the spy craft family.
systems the requests for them have increased recently for
Cryptography scrambles a message so it cannot be understood and the fast development of the Internet publicly.
generates cipher text. Steganography word is derived from Greek,
literally means “Covered Writing”. Steganography is the art of hiding
Cryptography is the study of mathematical techniques
the existence of data in another transmission medium to achieve secret related to aspects of information security such as
communication. It does not replace cryptography but rather boosts confidentiality, data integrity, entity authentication, and
the security using its obscurity features. It includes vast ways of secret data origin authentication. In addition, Cryptography is also
communications methods that conceal the message’s existence. These known as the science of secret writing. The goal of
methods are including invisible inks, microdots, character
cryptography is to make data unreadable by a third party.
arrangement and covert channels & spread spectrum
communications. Cryptography algorithms are divided into symmetric
In Cryptography, the meaning of data has been changed. So, it (secret-key) and asymmetric (public-key) network security
makes intention to the hacker to hack or destroy the data. In our protocols. Symmetric algorithms are used to cipher and
proposed paper, we implement a method by mixing both decipher original messages (plaintext) by using the same
Cryptography and Steganography for Information security. It not key. While Asymmetric algorithms uses public-key
only changes the meaning of data but also hides the presence of data
from the hackers. In order to secure the transmission of data, cryptosystem to exchange key and then use faster secret-
Steganography has to be implemented that allow information to be key algorithms to ensure confidentiality of stream data. In
sent in a secure form in such a way that the only person able to Public-key encryption algorithms, there is a pair of keys,
retrieve this information is intended recipient. one key is known to the public, and is used to encrypt
In this paper we proposed a method which describes two stages for information to be sent to a receiver who owns the
sending the information securely by using the Public-key
Cryptography and Steganography based on matching method. This is
corresponding private key. The private and public keys are
done in following steps: both different and need for key exchange.
1. Encrypt the message using any one of the popular Public-
Key Encryption Algorithms, so that only authorized parties can
Steganography is the science of hiding selected
only be able to read the message. information from a third party. Therefore, steganography in
2. Find and share stego-key between the two communication contrast with cryptography, where the existence of the
parties over insecure networks by applying Diffie Hellman Key message is clear, but the meaning is obscured.
exchange protocol.
3. Sender uses the secret stego-key to select pixels that it will be Steganography applications conceal information in
used to hide the message obtained in first step. Each selected other, seemingly innocent media. Steganographic results
pixel used to hide 8 bits of information. may masquerade as other file for data types, be concealed
This steganographic protocol is more efficient than LSBs. It produces
matching between the data bit parts and selected or least significant
within various media, or even hidden in network traffic or
bits of each pixel. disk space. There are many ways in which information and
Keywords: Public-Key Cryptography, Steganography, Stego-key, data can be exploited to conceal additional information.
Diffie-Hellman, LSBs.
For many years Information Hiding has captured the
1. INTRODUCTION imagination of researchers. Digital watermarking and
steganography techniques are used to address digital rights
Cryptography and Steganography are often interrelated management, protect information, and conceal secrets.
and share the common goals and services of protecting the Information hiding techniques provide an interesting
confidentiality, integrity and availability of information; challenge for digital forensic investigations. Information
which are some of the most important fields in computer can easily traverse through firewalls undetected.
security. Cryptography and steganography are methods of
transferring private information and data through open

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This paper proposes a new approach to public-key An analogy that can be used to understand the
steganography based on matching method to hide the secret advantages of an asymmetric system is to imagine two
information inside 24-bit image file. In the proposed people, SENDER and RECIPIENT, sending a secret
method, the stego-key is generated by applying a public message through the public mail. In this example, SENDER
key exchange protocol which is based on discrete logarithm wants to send a secret message to RECIPIENT, and expects
hard problem such as Diffie Hellman. a secret reply from RECIPIENT.
2. RELATED WORK: PUBLIC-KEY CRYPTOSYSTEM With a Symmetric-key system, SENDER first puts the
secret message in a box, and locks the box using a padlock
During the early history of cryptography, two parties
to which he has a key. He then sends the box to
would rely upon a key using a secure, but non- RECIPIENT through regular mail. When RECIPIENT
cryptographic, method; for example, a face-to-face meeting receives the box, he uses an identical copy of SENDER's
or an exchange via a trusted courier. This key, which both key (which he has somehow obtained previously, maybe by
parties kept absolutely secret, could then be used to a face-to-face meeting) to open the box, and reads the
exchange encrypted messages. A number of significant message. RECIPIENT can then use the same padlock to
practical difficulties arise in this approach to distributing send his secret reply.
keys. Public-key cryptography addresses these drawbacks
so that users can communicate securely over a public In an Asymmetric-key system, RECIPIENT and SENDER
channel without having to agree upon a shared key have separate padlocks. First, SENDER asks RECIPIENT
beforehand. to send his open padlock to him through regular mail,
keeping his key to himself. When SENDER receives it he
An asymmetric-key cryptosystem was published in 1976 uses it to lock a box containing his message, and sends the
by Whitfield Diffie and Martin Hellman, who, influenced locked box to RECIPIENT. RECIPIENT can then unlock
by Ralph Merkle's work on public-key distribution, the box with his key and reads the message from SENDER.
disclosed a method of public-key agreement. This method To reply, RECIPIENT must similarly get SENDER's open
of key exchange, which uses exponentiation in a finite
padlock to lock the box before sending it back to her.
field, came to be known as Diffie–Hellman key exchange.
The Diffie-Hellman key exchange protocol was the first The critical advantage in an asymmetric key system is
system to utilize public-key or two-key cryptography. For that RECIPIENT and SENDER never need to send a copy
this reason, it is sometime called as Asymmetric of their keys to each other. This prevents a third party
encryption. This was the first published practical method (perhaps, in the example, a corrupt postal worker) from
for establishing a shared secret-key over an authenticated copying a key while it is in transit, allowing said third party
(but not private) communications channel without using a to spy on all future messages sent between SENDER and
prior shared secret. RECIPIENT. So in the public key scenario, SENDER and
RECIPIENT need not trust the postal service as much. In
2.1 Public-key Cryptography: addition, if RECIPIENT was careless and allowed someone
Public-key cryptography refers to a cryptographic else to copy his key, SENDER's messages to RECIPIENT
system requiring two separate keys, one to lock or encrypt would be compromised, but SENDER's messages to other
the plaintext, and one to unlock or decrypt the cipher-text. people would remain secret, since the other people would
Neither key will do both functions. be providing different padlocks for SENDER to use.
Public key exchange cryptosystem eliminates the key
distribution problem by using two keys, a private and a
public key. By exchanging the public keys, both parties can
calculate a unique shared key, known only to both of them.
The Diffie-Hellman Algorithm for Key Exchange
SENDER must do the following:
1. Choose a prime numbers p randomly, and choose two
integer numbers a and g.
FIGURE 1: PUBLIC-KEY CRYPTOGRAPHY PROTOCOL 2. Compute the A (SENDER's public key), as follows:
One of these keys is published or public and the other is A = ga mod p.
kept private. If the lock/encryption key is the one published
3. Send the public value A to RECIPIENT.
then the system enables private communication from the
public to the unlocking key's owner. If the 4. Compute the secret value K, as follows: K = Ba mod p.
unlock/decryption key is the one published then the system
serves as a signature verifier of documents locked by the RECIPIENT must do the following:
owner of the private key. 1. Choose an integer numbers b randomly.
In the Diffie–Hellman key exchange scheme, each party 2. Compute the B (RECIPIENT's public-key), as follows:
generates a public/private key pair and distributes the
public key... After obtaining an authentic copy of each B = gb mod p.
other's public keys, SENDER and RECIPIENT can compute 3. Send the public value B to SENDER.
a shared secret offline.
4. Compute the secret value K, as follows: K = Ab mod p.

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SEND
DER RECIPIENT losslless method depends
d on thee inability of human
h optic to
t
diffeerentiate any changing
c in immage color orr sound qualityy.
Secret Public Calculates Sends Calcuulates Public Secret
S The 16-bit sound file and 24-biit map (BMP)) image file arre
typiccally used foor steganograaphic purposees. Image annd
a p, g p,g b
sounnd files are considered
c a well known carrier meddia
a p, g, A a
g mod p = A A p, g b canddidates for hidding informattion that ease the operationns
on steganography
s y. Therefore, we are focu using on 24-bbit
p, g, imag ge file in our proposed
p metthod for this study.
s However
a p, g, A B gb modd p = B b theree are many proposed
p stegganography methods
m amonng
A, B
them
m one of the poopular methodds is Least Sig gnificant Bit.
p, g,
a, s p, g, A, B Ba mod p = s Ab mod p = s b, s Leeast significaant Bit (LSB B) insertion is i a commonn,
A, B simpple approach to embeddinng informatio on in a cover
imagge[1]. The leaast significannt bit of somee or all of thhe
TABLE 1: DIFFIE-HELLMA
AN KEY EXCHANG
GE PROTOCOL bytes inside an image
i is channged to a bitt of the secrret
messsage. When using
u a 24-bit image, a bit of each of thhe
The securiity of the Diffie-Hellma
D an key exchhange red, green and bluue colour com mponents can be used, sincce
pprotocol is based on the strrength of the discrete algorithm they are each reprresented by a bbyte. In other words, one caan
a the size of the key usedd. However, the
and t Diffie-Helllman storee 3 bits in eacch pixel. An 512 × 512 piixel image, caan
p
protocol is connsidered securre against bruute force attackk if p thus store a total amount of 7,,86,432 (512x x512x3) bits or
o
a g are chossen properly (Diffie, et al.,, 1976). Curreently,
and 983004 bytes of em mbedded data [2]. For exam mple a grid for 3
thhe solving of the Diffiie-Hellman discreted logaarithm pixells of a 24-bit image
i can be as follows:
p
problem will make many other public--key cryptosyystem
innsecure. The Diffie-Hellm man key exchhange has a high (001101101 00011100 11011100
0)
leevel of the security beccause Diffie--Hellman prootocol
(101100110 11000100 00001100
0)
d
depends on laarge prime nuumbers whichh exceeds 10224 bit
(Diffie, et al., 1976, Elaine et
e al., 2006). (110010010 10101101 01100011
1)
2 Steganogrraphy:
2.2 When
W mber 200, whhich binary reepresentation is
the num
110001000, is embedded into thee least significcant bits of thhis
Steganograpphy is the scieence of writinng hidden messages
part of the image, the resulting grid is as follo
ows:
too guarantee information which is acccessible only by
a
authorized parrties, and to thhe one has thee secret key and
a is (001101101 00011101 11011100
0)
innaccessible to t others. It I is the prractice of hidingh
innformation usually text messages,
m insidde other file (host (101100110 11000101 00001100
0)
f
file). This pracctice of hidingg information (steganographhy) is (110010010 10101100 01100011
1)
n
normally called stego. Stteganographicc systems caan be
g
grouped by thhe type of covvers used (graaphics, sound,, text, Although
A the number was embedded in nto the first 8
e
executables) o by the technniques used too modify the covers
or bytes of the grid, only the 3 uunderlined bitts needed to be b
s
such as innsertion, subbstitution, trransform doomain nged accordingg to the embeedded messag
chan ge. On averagge,
teechniques, sppread spectrum m techniques, statistical meethod, only
y half of the biits in an imagee will need to be modified to t
d
distortion tecchniques, andd cover genneration metthods. hide a secret messsage using thhe maximum cover size [22].
Information caan be hidden (or embeddeed) inside anyy type Since there are 256 2 possible intensities off each primarry
o multimediaa file; image files are the most widely used
of colouur, changing the LSB of a pixel reesults in smaall
tooday. The hosth files cann then be exxchanged oveer an chan
nges in the intensity
i of tthe colours. These
T changees
innsecure mediuum without anyone
a knowinng what reallyy lies cann
not be perceiveed by the hum man eye - thuss the message is
innside of themm. successfully hiddden. With a w well-chosen im mage, one caan
n hide the messsage in the least as well as second to leaast
even
signiificant bit andd still not see tthe difference [1].
Secrret
Messaage In
n its simplest form, LSB m makes use off BMP imagees,
sincee they use loossless comprression. LSB steganographhy
has also been deeveloped for use with oth her image file
mats. The 24-bbit image is typpically used in
form n LSBs methood
Cover Steganography Stego to hiide the secret information.
i
Object Technnique Object
In
n the above example,
e conssecutive bytess of the imagge
data – from the first
f byte to thhe end of the message – arre
usedd to embed thee information. This approach is very eassy
Stego Key to detect
d [3]. A slightly morre secure systtem is for thhe
sendder and receiveer to share a ssecret key thatt specifies onlly
certaain pixels to be
b changed. S Should an adv versary suspect
FIGURE 2: STEGA
ANOGRAPHY PROTOCOL
that LSB steganography has been used, he has no way of o
Computer Steganograph
S y is basicallyy categorizedd into knowwing which pixels to target without the secret key [44].
tw
wo methods; lossless methood and loss meethod. This process actuaally needs a seecret key that is called stegoo-
key. The stego-keyy is used to coontrol the steg
go process succh
Lossless meethod is a commputerized im mage or soundd files he selection off pixels. The sselected pixell is then will be
as th b
ccan be replaceed without losiing their functtionality. Sincce the usedd to embed thee secret binaryy information.

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3. PROPOSED METHOD
Sender Recipient
3.1 Public Steganography in various selected regions of
an image:
Original Original
The proposed method describes two steps for hiding the Message Message
secret information by using the public steganography based (Plain Text) (Plain Text)
on matching method in different regions of an image.
The First step is converting the Plain text message into Public Key Public Key
cipher text using Public-key Encryption algorithm. Encryption Decryption
The next step is to find the shared stego-key between the
two communication parties (SENDER & RECIPIENT) over
Encrypted Encrypted
insecure networks by applying Diffie-Hellman Key Message Message
exchange protocol (as explained above). At the end the (Cipher Text) (Cipher Text)
protocol, each side recovers his/her received public key to
reach the shared values between them, that’s mean
SENDER & RECIPIENT have arrived same sego-key Stego Stego
value. Function Inverse
Stego F (x) Function Stego
The next step in the proposed method is that the sender Key F’ (x) Key
uses the secret stego-key to select pixels that it will be used Stego (S)
to hide. Each selected pixel is then used to hide 8 bits
binary information depending on the matching method Cover Medium (C)
which is summarized in four cases as shown by Table 2.
Since the 8 bits data will be compared with the selected
pixel's bytes, red, green & blue values respectively to DH Protocol
produce an array of binary values as 00, 01, 10, and 11.
FIGURE 3: PROPOSED METHOD WORKING PROCESS
SENDER's side, starts comparing to search the equality,
where, he takes data value and compare it with the value of 3.2 Problems and Possible solutions
the red color (± 7 – decimal value). As shown by Table 2,
case no. 1, if they are equal, then the value zero (00 – Having stated that LSB insertion is good for
binary value) is set to the array. Table 2, case no. 2, if the steganography, we can try to improve one of its major
data value and the red value are not equivalent then the drawbacks: the ease of extraction. We don't want that a
value will be compared with the green color, if they are malicious attacker be able to read everything we are
equals (± 7 – decimal value) then the array is set to be one sending.
(01- binary value). Table 2, case no. 3, if the data value and This is usually accomplished with two complementary
the green value are not equivalent then the value will be techniques:
compared with the blue color, if they are equals (± 7 –
decimal value) then the value two (10 – binary value) is set  Encryption of the message, so that who extracts it
to the array. Finally (refer to Table 2, case no. 4), If in case must also decrypt it before it makes sense
the secret data didn’t equal any of the previous three  Randomizing the placement of the bits using a
conditions then the LSBs method is used to embed the data cryptographical random function (scattering), so that
inside the selected pixel, and the value three (11 – binary it's almost impossible to rebuild the message without
value) is set to the array. In this case, the data value will be knowing the seed for the random function.
distributed as follows:
In this way, the message is protected by two different
1. The first three bits of the data are replaced by the three keys, acquiring much more confidentiality than before.
least significant bits of the red byte. This approach protects also the integrity of the message,
2. The second three data bits are replaced by the three least being much more difficult (we could say at least
significant bits of the green byte. computationally infeasible) to counterfeit the message.
3. The last two data bits are replaced by the two least The two most important issues in these problems are:
significant bits of the blue byte.  the choice of images
If 8 bit data ≈ Red Then Red value =  the choice of the format (24-bit or 8-bit, compressed
Case 1 00
(8 bit ) 8 bit data or not)
If 8 bit data ≈ Then Green value The cover image first of all must seem casual, so it must
Case 2 01
Green (8 bit ) = 8 bit data be chosen between a set of subjects that can have a reason
If 8 bit data ≈ Blue Then Blue value = to be exchanged between the source and the receiver. Then
Case 3 10 it must have quite varying colors, it must be "noisy", so that
(8 bit ) 8 bit data
the added noise is going to be covered by the already
Case 4 Otherwise Use LSBs Method 11 present one. Wide solid-color areas magnify very much any
little amount of noise added to them.
TABLE 2: THE FOUR MAIN CASES IN THE PROPOSED PUBLIC-KEY STEGO

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Second, there is a problem with the file size that involves used the matching method to get identical pixel's bytes.
the choice of the format. Unusually big files exchanged However, the proposed method resorts to the LSBs method
between two peers, in fact, are likely to arise suspicion. to distribute the secret data in case if the 8 bit of data is not
Since we need to have small image file sizes, we should matched with any of the previous three bytes (red, green,
resort in using 24-bit images, because their size is more and blue).
likely to be considered as normal.
CONCLUSION
Steganography is a really interesting subject and outside
of the mainstream cryptography and system administration
that most of us deal with day after day. As steganography
becomes more widely used in computing there are issues
that need to be resolved. There are a wide variety of
different techniques with their own advantages and
disadvantages.
This paper has shown the possibility of using matching
method in different regions of an image in public
FIGURE 4: THE RESULT OF EMBEDDING THE TEXT WITH S-TOOLS steganographic protocol. The security of the proposed
steganography depends on Encryption algorithm and
Diffie-Hellman public key exchange protocol. We can add
4. RESULTS AND DISCUSSION more security to the information which needs to be
We implemented the public-key steganography based on transmitted through public networks using this method.
matching method in different selected regions of an image ACKNOWLEDGMENTS
to show the performance of the proposed method.
In our implementation, we used 600×400 bitmap image I thank Dr. D. Srinivasa Kumar, for his helpful feedback
file to hide 5 KB text data. As discussed earlier, both of the on this work. I would also like to thank my family and
two communication parties should find the secret key friends who encouraged me in doing this work.
(stegokey) first by applying Diffie-Hellman public-key REFERENCES
exchange protocol to perform high level of security.
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