Encryption of Decomposed Image by using ASCII Code based Carrier Signal

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 2962
Encryption of Decomposed Image by using ASCII Code based Carrier
Signal
Reema Dhiman1, Butta Singh2
1 Student Mtech, Department of Electronics and Communication Engineering, GNDU RC, Jalandhar, India.
2 Assistant Professor, Department of Electronics and Communication Engineering, GNDU RC, Jalandhar, India.
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Abstract - Encryption is one of the best method to secure
picture data. An ASCII code based carrier signal and image
decomposition has been outlined in this paper. Image
decomposition is an efficienttechniquewhich isusedforimage
encryption and this decomposed image is further proceeding
for encryption process. The Carrier image is used for
encryption process which is to be generated by using ASCII
Codes. A sturdy password is used to encrypttheimage withthe
help of carrier. This method is applied on various images for
the calculation of image parameters. After evaluatingallthese
aspects, parameters like correlation, entropy is calculated for
both the encrypted as well as decrypted image.
Key Words: Carrier Image, ASCII Code, Entropy,
Correlation
1. INTRODUCTION
Security issues [1] have turned out to be increasingly
genuine with the fast improvement of the web and the
approach of advanced cell phones that use a lot of private
data, particularly pictures, which are presented to the
system. However, because of data size and the high excess
among the crude pixels of a computerized picture,
conventional encryption algorithms such as data encryption
standard (DES), international data encryption algorithm
(IDEA) and advanced encryption standard (AES) might not
be appropriate for image encryption. To forestall image data
spillage, many new image encryption algorithms have been
proposed by using different techniques, including chaos
theory [2], DNA coding [3], and compressed sensing [4].
Information security is one of the significant issues in the
current information age, as there is a continuous
development in the pace at which the information is being
distributed [5]. There are few techniques for image
encryption which manages their own thoughts or ideas. In
couple of algorithms, encryptionprocessdependsjustonthe
catch phrases; however in some different algorithms they
utilize some carrier image for encryption.Becauseofthis,we
have a thought to combine the current algorithms to get
another way for encryption by taking the benefits of
individual techniques. Consequently we concoct the idea of
decompose the original image and create carrier for Image
encryption to get profoundly contorted Image. Panduranga
et al proposed [6] a secure method by hybridizing the SCAN
pattern and the carrier image for image encryption to get
extremely distortedimage.Theydevelopedtheperceptionof
generating the carrier image withthehelpofdistinctivecode
called as 4 out of 8-code. The proposed hybrid approach for
image encryption gives very superior results but the
password used in this algorithm is not secure. So, in our
proposed approach, ASCII codes are used for generating the
carrier image and this carrier is used further for encryption
process.
2. PROPOSED METHODOLOGY
Encryption of an image should be possible at various stages
and in numerous ways. If the encryption process is only in
single stage then security is less as contrast with multistage
encryption [6]. In our proposed mechanism, the
decomposition of image is carried out over various levels
and this decomposed image is used for encryption process.
Now, the following steps are used for both the encryption
and decryption process.
2.1 Encryption Process
The encryption process is implemented in MATLABand
it involves the following steps:
Step 1: Load an image for encryption.
Step 2: Decompose the image into various levels in vertical
and horizontal direction. This decomposition is carried out
at 4 levels.
Step 3: Enter the prototype for arranging the decomposed
blocks at level 1, level 2, level 3 and level 4 as shown inFig-1.
Step 4: Enter the password for encryption and generate the
carrier image by using ASCII code. The password used in the
encryption process is '!~ "z#y$x $w%v &u*t+s,r-q.p/o 1n 2m
3l4k 5j 6i 7h8g 9f:e;d <c=b>a?`@_A^BCZDYEXFWGVHUITJS
KR LQMP NO'. With the help of this password,a carrierimage
is generated.
Step 5: Add the carrier image withthedecomposedimageas
shown in Fig-2.
Step 6: Finally, we get an encrypted image.

Shuffled Image
a) b)
Shuffled Image Shuffled Image
c) d)
Fig-1: Decomposed Images at a) Level 1 b) Level 2
c) Level 3 d) Level 4
Fig-2: Addition of Carrier with decomposed Image
In this way, encrypted image is generated at the transmitter
side. Now, this image is passing through the channel and
received at the receiver end.
2.2 Generation of Carrier Signal by using ASCII
Codes
Here we are characterizing another code called ASCII
code. This code is of 8 bit length and it gives an encoding of
128 characters.
log2 128= 7
A set of 94 conceivable combinations of the ASCII code
words and each code is allotted to an alphanumeric
character and additionally special characters. Depending
upon the keyword, carrier image is generatedandutilized as
a part of the addition process to create an encrypted image.
In this we choose the ASCII codes that is used for the
generation of strong password that comprises of special
characters which is having binary values as well as DEC
values. For Ampersand, the ASCII value is 38, for single
quote, the ASCII value is 39, for leftand rightparenthesis, the
ASCII values is 40 and 41. For Asterisk, the ASCII value is 42,
for Plus, the value is 43, for comma=44, minus=45,
period=46, slash=47, zero=48, One=49, Two=50, Three=51,
Four=52, Five=53, Six=54, Seven=55, Eight=56, Nine=57,
Colon=58, Semicolon=59, less than=60, equality sign=61,
greater than=62, question mark=63, at sign=64, capital
letters= 65 to 90, left squarebracket=91,Backslash=92,right
square bracket=93, caret / circumflex=94, Underscore=95,
grave / accent=96, small letters=97 to 122, left curly
bracket= 123- C3, vertical bar= 124-C4, right curly bracket=
125- C5, Tilde=126-C6, Delete=127- C7.
Following are the steps which are used to generate the
carrier image.
Step 1: Enter the password for encryption.
Step 2: Search the alphanumeric characters and symbols in
the ASCII code words.
Step 3: The binary values of ASCII code words is converted
into the decimal values.
Step 4: With the help of these decimal values, the carrier
image is generated with different patterns.
Hence, in this way, carrier image is generated for the
encryption process.
2.3 Decryption Process
The decryption processisimplementedinMATLABandit
involves the following steps:
Step 1: At receiver end, the encrypted image is received.
Step 2: Enter the password for decryption and generate the
carrier image by using ASCII code words.
Step 3: When the password match then it will subtract the
encrypted image from carrier image and we get an original
decomposed image.
Step 4: Enter the prototype for re-arranging the
decomposed blocks and then we get a decrypted image.
The above steps show the encryption as well as
decryption process.
3. RESULTS AND DISCUSSION
This section describes the implementation of proposed
methodology for different images. Here, the methodology is
used on different images and its results will be calculated.
The essential requirement to implement our approach are
MATLAB of version R2013a or higher. The parameters used
are correlation analysis and entropy analysis as discussed
below:
Carrier Image Encrypted Image
=+

3.1 Entropy Analysis
The mathematical determination of randomness in an
image and that can be utilized to describe the texture of the
input image quantity [7]. The Table-1 shows the results of
different images at different level of decomposition.
Table -1: Entropy Analysis of encrypted and decrypted
image
Image Entrop-
y of
original
image
Image
Decop-
osition
Level
Entropy
of
encrypte-
d image
Entropy
of
decrypte-
d imageOriginal Image
Lena
7.4571
Level 1 7.5193 7.4571
Level 2 7.5202 7.4571
Level 3 7.5197 7.4571
Level 4 7.5192 7.4571Original Image
Peppers
6.9924
Level 1 7.5115 6.9925
Level 2 7.5109 6.9925
Level 3 7.5117 6.9925
Camera-
man
7.1225
Level 1 7.5307 7.1227
Level 2 7.5306 7.1227
Level 3 7.5247 7.1227
Boats
7.2154
Level 1 7.5245 7.2154
Level 2 7.5249 7.2154
Level 3 7.5247 7.2154
Baboon
7.3738
Level 1 7.5136 7.3738
Level 2 7.5142 7.3738
Level 3 7.5310 7.3738
Level 4 7.5142 7.3738
The above table shows the entropy of original, encrypted
and decrypted images for different images at all the
decomposition levels. As observed the entropy of encrypted
image is increases as compared to the original image which
shows that the encrypted image has superior randomness.
Also, there is a slight difference between the original and
decrypted image which shows ouralgorithmgivesimproved
results.
3.2 Correlation Analysis
The effect of the image decomposition is related to the
correlation of adjacent pixels. In order to calculate the
correlation between the plain image and the original image
then different levels of decomposition are analyzed for both
the original and the plain image. Following are the formulae
which are used to calculate the correlationcoefficientsin the
horizontal, vertical and diagonal directions.
Where E(x) and D(x) are the mean and standard
deviation of the corresponding gray scale values of two-
adjacent pixels in the image and N is the number of duplets
(x,y) obtained from the image. The Table-2 shows the
various value for correlation.
Table -2: Correlation Analysis of encrypted and decrypted
image
Image Name of
Image
Image
Decomp
-osition
Level
Correlat
-ion for
encrypt-
ed with
original
image
Correlati
-on for
decrypt-
ed with
original
imageOriginal Image
Lena Level 1 0.0072 1
Level 2 0.0086 1
Level 3 0.0063 1
Level 4 0.0273 1Original Image
Peppers Level 1 -0.0110 1
Level 2 -0.0167 1
Level 3 0.0175 1
Camera-
man
Level 1 -0.0268 1
Level 2 0.0087 1
Level 3 0.0287 1
Boats Level 1 -0.0372 1
Level 2 0.0152 1
Level 3 0.0287 1
Baboon Level 1 0.0102 1
Level 2 0.0089 1
Level 3 0.0275 1
Level 4 0.0192 1

As observed the correlation of encrypted image is highly
correlated as compared to the original image. For effective
encryption, the correlationcoefficientshouldbeclosetozero
which can be observed in the above table. Also, the
correlation analysis between the original and decrypted
image is nearly one which means the the original and
decrypted image is same.
4. CONCLUSIONS
An alternative approach isproposedforimage encryptionin
which carrier image is generated by using ASCIIcodewords.
Here, the image is decomposed into 4 levels and after that
the decomposed image is used as an input image for
encryption process. A sturdy passwordisgeneratedbyusing
ASCII code words and then we get a highly encrypted image.
Calculation of entropy and correlation analysis between
encrypted and decrypted images is done for all the 4 levels.
This chapter concludes that the proposed algorithm for
image encryption gives better results as compared to other
encryption process. For the sake of complexity,weuseASCII
code words in which we can generate the carrier image by
using alpha-numeric as well as special characters. We
applied this approach on various imagesatdifferentlevels of
decomposition. i.e. level 1, level 2, level 3 and level 4 for the
complexity of algorithm. From all the experimental results,
we conclude that our algorithm is best suited for encryption
process.
ACKNOWLEDGEMENT
I would like to express my sincerest thanks to Dr. Butta
Singh, Department of Electronics and Communication
Engineering, who gave me support and encouragement and
also provided me valuable and countless resources.
REFERENCES
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[2] Xing-YuanWang, Sheng-Xian Gu, Ying-Qian Zhang,
“Novel image encryption algorithm based on cycle shift
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[3] RasulEnayatifar, Hossein JavedaniSadaei, Abdul
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[4] NanrunZhou, AidiZhang, FenZheng, LihuaGong, “Novel
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[5] Vinod patidar, N.K. Pareek, K.K. Sud, “A new
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