International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013
A Review Based Study of Hybrid Security Schemes
Based on Compression, Encryption and Steganography
Jyoti Gaba#1, Dr Mukesh kumar sharma#2
#1
M.Tech Scholar, CSE Department, T.I.T&S Bhiwani (M.D.U. Rohtak), Haryana, India
#2
Professor, CSE Department, M.D.U. Rohtak, Haryana, India
Abstract— Information exchange over the network is no more
secure. Intruders and eavesdroppers always try to expose the
secret information either to take benefit out of it or just to show
their technical expertise. Encryption has been the tool to shelter
the text for a long time. Its main downside is that it draws
attention of unauthorized people due to the fact that message is
incomprehensible. Steganography avoids attention by hiding the
information behind some digitally representative media, but, it
carries the text as it is. The threats from the attackers have
increased tremendously in recent years and neither of these two
tools is secure enough in solitary. These two tools can be
combined to give the attacker a tough fight in discovering the
text. Lossless compression can be used to trim down the
information before encoding it. It can be united with encryption
and steganography so as to make the task even more complicated
for invader. This paper reviews some algorithms uniting these
techniques.
Keywords— Cryptography, Steganography, Compression
I. INTRODUCTION
the media.
Encryption makes the text unintelligible.
Steganography thwarts suspicion on the presence of data. The rest
of the paper is organized as follows. Section II provides some
background on cryptography, steganography and compression
techniques. Section III reviews some algorithms that combine
these three. Section IV concludes the paper.
II. BACKGROUND
A. Cryptographic Techniques
Three types of algorithms
cryptography:
are
used
generally
in
1) Symmetric Key Cryptography (SKC): Uses an identical
key for both encryption and decryption. These algorithms are
fast to implement. But in these techniques data is secure only
as long as the key is secure so it must be delivered with
utmost security.
2) Asymmetric Key Cryptography (PKC: Uses one key for
encryption and a different for decryption. These are drastically
slow in operation.
Cryptography and steganography are well accepted
techniques intended to enable secure data exchange between
two parties. These techniques use different approaches to
3) Hash Functions: Uses a mathematical transformation to
achieve this objective. The word cryptography is derived from
the Greek word kryptos, meaning ’hidden’. So, cryptography irretrievably "encrypt" information. Therefore, once the plain text
encrypts the text thus changing its meaning and making it is enciphered to generate the cipher text, the process cannot be
unintelligible.
reversed to generate plain text back from cipher text. These are
The word steganography is derived from the Greek words
steganos, meaning ’covered’, and graphy, meaning ’drawing’ generally used in password verification.
or ‘writing’. Steganography is the art and science of hiding
information so that its presence cannot be detected [1]. As a B. Steganography Techniques
result, steganography hides the existence of text and does not
In steganography, information can be hidden behind vast variety
raise suspicion in mind of the intruder [2]. If someone
suspects the presence of information, steganography has failed of media like images, audio, video, text, or some other digitally
to serve its purpose [3]. Compression is the technique used to representative code. There are quite a lot of appropriate carriers
compress plain text to generate compressed text in order to that can be used as the cover-object [4]:
decrease space utilization. Additionally, it reduces the i) Protocols such as TCP, IP and UDP.
ii) Audio files having formats such as midi, avi, mpeg, mpi
bandwidth requirements for transmitting the text.
and voc.
If we follow three steps: Initially, compress the data, then, encrypt
iii) Text files such as html and java.
it and finally, mask it behind some other media, it can provide
iv) File and Disk that can hide and append files by
incredible security. Thus, these three techniques, if combinedcan
using the slack space
can provide unbreakable security of confidential data.
v) Image files such as bmp, gif and jpg, including both color
Compression reduces storage space and bandwidth requirements to
transmit data. Moreover, it requires less data to be hidden behind
and gray-scale.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013
Basically Steganography techniques can be characterized as
follows [8]
1) Text Steganography: It is one of the toughest types of
coding as it involves altering the structure of a text file to hide
secret text. In this case, huge amounts of data are required to
hide the text. Its prevalent techniques are line-shift coding,
word-shift coding, feature coding etc.
Data compression techniques can be grouped into two
categories: lossy and lossless.
1) Lossy Compression techniques: Compresses data at the
cost that data cannot be exactly recovered as it was before
compression. The reason being these techniques remove
redundant information that cannot be reinstated. These are
generally used to compress images, audio, video etc. But these
techniques provide a larger compression ratio than lossless
ones.
2) Lossless Compression: These techniques compress data
such that it can be retrieved as it is after decompression.
Compression ratio achieved by these techniques is usually
smaller and more processing power is required to accomplish
the operation. Text files are generally compressed by this
technique. Various algorithms for lossy compression are run
length encoding, Huffman encoding, LZW encoding etc.
2) Image steganography: In this, the secret text is hidden
behind a cover image by modifying some bits of its pixels. It
is an effective technique because of the limitations of human III. ALGORITHMS C OMBINING C RYPTOGRAPHY, STEGANOGRAPHY AND
eye to identify minute change of colours. Its prevalent
C OMPRESSION
techniques are Least Significant Bits, Masking and filtering,
A. CCS (Compressed Crypto Stegno) Scheme
transformations etc.
To meet the ever increasing security needs G. Manikandan,
N. Sairam and M. Kamarasan proposed CCSM[6]
(Compressed Crypto Stegno Model) that unites three practices
described above. This proposal uses LZW lossless
compression algorithm to compress the data at the initial step.
The data can be perfectly reproduced at the other end due to
the lossless behavior of this algorithm. After compressing the
C. Comparing Cryptography with Steganography
data, it is encoded by BlowFish algorithm. BlowFish is a
Basically, both serve the same purpose. However, they fiestel based symmetric block cipher that comprises of 16
differ significantly. Cryptography hides the contents of a iterative rounds. This approach uses a modified F-function
secret message from malicious people, whereas steganography that substitutes 2 addition operations and one XOR operation
even conceals the existence of the message. Both can be by 2 XOR operations, one addition operation and one circular
shift operation. After enciphering the compressed text, the
contrasted as follows [5]
resultant data is masked behind an image using the LSB
(Least Significant Bit) approach which is a relatively simple
1) Known vs. unknown: Cryptography passes the message
technique. It substitutes the LSB of some selected pixels by a
consciously whereas steganography unsuspectingly.
bit from the cipher text. Thus this technique hides 3 bits in
every 24 bits value of a pixel. This results in a very
2) Detection vs. discovery: Cryptography conceal the contents of
insignificant alteration of the cover image that is
communication thus preventing its discovery whereas
imperceptible to human eye. After performing these three
steps at the sender side, exactly mirror image of these steps is
steganography hides the detection of the communication
performed by the other party. Thus, first extracting the
masked message from the cover image, then, decoding it and
3) Structure of message: Cryptography scrambels the structure
ultimately decompressing it to get the intended plain text. The
of confidential message whereas steganography does not.
following diagram depicts the sender side operations
4)
Technology: Cryptography has a huge range of performed in this model
algorithms and common technology whereas for
steganography technology is still being developed.
3) Audio steganography: In this technique, secret text is
masked behind an audio file. It is also a complex technique as
humans can determine a slight variation in audio quality.
Common techniques under this category are LSB coding,
phase coding, spread spectrum, echo hiding etc.
D. Compression Techniques
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013
C.
Information Hiding Using LSB Steganography and
Cryptography
This scheme proposed by S. Gupta, A. Goyal and B.
Bhushan combines public key cryptosystems such as RSA and
Diffie Hellman with LSB steganographic method [9]. The
scheme first encrypts the message with either RSA or Diffie
Hellman and then hides the binary equivalent of the encrypted
message behind Least Significant Bits of the carrier image.
The transmitted image when received at other side is used to
extract the embedded bits of the message from Least
Significant Bits. The same algorithm used for encryption at
the sender side is used at the receiver side to decrypt the
extracted bits. The authors have experimented by hiding
varying number of bits in each pixel of the carrier image. The
results indicate that as the size of the image increases, time
complexity increases proportionally. Moreover, with the
increase in number of bits hidden behind the image,
complexity also increases. RSA provides more security when
united with steganography but increases the time complexity
as compared to Diffie Hellman.
B. CrypSteg Algorithm
This scheme proposed by P. Bharti and R. Soni combines
both cryptography and steganography to satisfy the needs of
secure communication such as security, capacity and
robustness [7].
D. Twelve Square Substitution Cipher And Index Variable
Based Steganography
This approach proposes a new encryption algorithm namely
twelve square [10]. It can be used to encipher alphabets, digits
and special characters too. It uses two different tables
comprising of 6 squares each.
In the encryption process, the key value is concatenated 8
times and first 8 characters are selected. ASCII values of these
chosen characters are added together and the resultant is
divided by 1000 to achieve a three digit number. Let it be
denoted by N1N2N3. 1st ,4th ,7th ……… characters of the
plain text are shifted by N1, 2nd ,5th ,8th ……… characters are
shifted by N2 and 3rd ,6th ,9th ……… characters are shifted by
N3.
In the steganography process, the image is partitioned into
4*4 pixel blocks. The enciphered data is converted to binary
and masked behind Least Significant bits (LSB) of the
diagonal pixels. Thus, 4 bits are hidden behind 4*4 pixel
block. This algorithm is very competent for little amount of
data and for the cases where cover image has its pixels
homogenously scattered.
First table is used to encrypt alphabets and second table for
digits and special characters. For first character square 1st &
4th are used. The position of the character in 1st square is
located and the corresponding character at the same location
in 4th square is substituted for it. For 2nd character, 2nd and 5th
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013
squares and for 3rd character, 3rd and 6th squares are used,
wounding to 1st and 4th square for the next character and so on.
After encrypting the text, both the cipher text and the carrier
image are converted to binary form. The number of bytes in
the cipher text is divided by 3 to calculate an index variable
denoted by p. This index variable determines the particular
bits in the pixel behind which the bits of cipher text will be
masked. For p=0, 6th and 7th bits, for p=1, 7th and 8th bits and
for p=2, 6th and 8th bits of the pixel are used to hide the bits of
the cipher text. The value of p is incremented with every pixel.
This method is very much preventive against frequency
analysis attack due to the nature of the twelve square
substitution cipher.
E. Transmitting Cryptographic Data Through Steganography
This technique[11] combines the cryptography and
steganography approaches. To begin with the data is
enciphered with the assistance of a secret key and cipher text
is produced as a result. The encoded text is then embedded
and covered behind the cover-image. Finally, the stego-image
is transmitted to the other party. The other side performs the
reverse process. It first filters the received image and restores
the pixels so as not to alter the original cipher text. Then it
retrieves the plain text by decrypting the cipher text.
F.
A New Horizon in Data Security by Combining
Cryptography And Steganography
This paper designs a new system that comprises of four sub
components[12]
IV. CONCLUSIONS
Looking at the ever growing security requirement, the
cryptography and the steganography techniques are not
sufficient single-handedly to protect the secret data.
Cryptography draws attention towards the incomprehensible
text and attracts the malicious users to break it. Steganography,
though do not arise suspicion but, if compromised, may reveal
the secret data in its original form. These can be treated as one
entity to enhance the protection. They can further be
supplemented with compression to remove redundant data
before hiding the text which will also reduce storage
requirements. This paper provides a review of some common
algorithms and schemes that combine two or all three of these
techniques. Future work may encompass different
combinations of cryptography and steganography techniques
so as to decrease the time complexity and to boost the security.
REFERENCES
[1]
1) Compression component: It compresses the input text by
Huffman encoding scheme
[2]
2) Crypto component: This unit enciphers the compressed
text by using the AES symmetric encryption scheme using
128 bit key. The resultant is converted to hexadecimal form.
[4]
3) Security module: This unit hides the first 7 hex values
and uses the rest of them to produce a key. It adds additional
security to the system
4) Stego-module: To begin with, capture 7 hex values from
above component and jumble these values using 64 bit key.
Now take a gray scale image and calculate its DCT. Hide the
coded text by modifying DCTs. To find stego-image apply
inverse DCT.
[3]
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[6]
[7]
[8]
[9]
[10]
[11]
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