An Adaptive Dual Image Encryption
Ramyashree A.N1
4th Sem, M.Tech (DECE)
Dept. Of Electronics & Communication Engineering.
Akshaya Institute of Technology, Tumkur
ramyanarayan.an26@gmail.com,
Abstract-Information must be secure in the fast
growing internet technology. To secure the
information encryption is also used. Integrity
and Cryptography are the core principles of
information security. Integrity means that data
cannot be modified undetectably. The hash
functions in cryptography are message integrity.
This paper presents an approach to improve the
entropy of an encrypted image using hill-cipher
and to provide authentication. Dual image
encryption process involves the following three
stages. In first stage, Hill-cipher with invertible
matrix or Hill cipher with non-invertible matrix
are applied, depending on the switch value. In
stage two each pixels of both the images are bitwise rotated and reversed to change the pixel
value. In third stage, higher nibbles in each pixel
of two resultant images are exchanged, finally
get encrypted images.
Keywords—Hill cipher, bit-rotation, nibble
exchange, entropy, SHA.
I.
INTRODUCTION
The advent of electronic commerce applications,
an urgent need to solve the issue of information
security in an open network environment is
required. Encryption is a method of transforming
original data, called plaintext or clear text, into a
form that appears to be random and unreadable,
which is called cipher text. Plaintext is either in a
form that can be understood by a person (a
document) or by a computer (executable code).
Once it is not transformed into cipher text, human
nor can machine properly process it until it is
decrypted. This enables the transmission of
confidential information over insecure channels
without unauthorized disclosure. When data is
stored on a computer, it is usually protected by
logical and physical access controls. When this
Manjunatha C.N2
Lecturer, Dept. Of Electronics & Communication
Engineering.
Akshaya Institute of Technology, Tumkur,
cnmmanjunath@gmail.com
same sensitive information is sent over a network, it
can no longer take these controls for granted, and the
information is in a much more vulnerable state.
So many methods for image encryption with some
advantages and disadvantages.
Panduranga H.T et. al [1] have presented a novel
image encryption technique using multi wave based
carrier image. Here carrier image pixels are created by
amplitude values of multiple sine waves generated by
alphanumeric password. S. R. M. Prasanna et. al[2]
presented an image encryption method with magnitude
and phase manipulation using carrier images. They
used the concept of one dimensional Discrete Fourier
Transform and carrier images for encryption purpose.
Ismail I.A et.al[3] presented novel technique for the
existing hill cipher algorithm. Here they used different
key for each block encryption. Panduranga H.T
et.al[4] a hybrid technique for image encryption which
employs the concept of carrier image and SCAN
patterns generated by SCAN methodology.
Although it involves existing method like SCAN
methodology. Carrier image is created with the help of
alphanumeric key word. Alphanumeric key generated
by 4 out of 8-code. Advanced Hill encryption
algorithm uses involutory matrix generation method
and key matrix is itself invertible. It is the a fast
encryption technique with normal hill cipher [5].
Bibhudendra Acharya et.al[6],to repair flaws in the
original hill cipher it uses involutory ,permuted and
reiterative key matrix. Novel digital image encryption
scheme using a secrete key of 144 bits. Here image is
divided into blocks and subsequently into colour
components. Each colour component is modified by
performing bitwise operation which depends on secret
key as well as a few most significant bits of its
previous and next colour component [7] Encryption
method [8] uses cover image which acts as key image
for encryption which is shared by both sender and
receiver and other. In the first step of encryption XOR
the cover image with informative image , and in the
next step resultant image is decomposed in to (n*n)
blocks which is passed to the hill cipher algorithm
to get encrypted blocks.
The organization of the paper is as follows:
following the introduction, section II explains the
concept of Bits Rotation & Reversal technique. Hill
Cipher technique is explained in Section III. SHA
explained in section IV The proposed method for
dual image encryption is explained in section V.
Section VI concludes this work and future
enhancement.
II.
So that the weight of each pixel is responsible for its
colour, the change occurred in the weight of each pixel
of input image due to Bits Rotation & Reversal
generates the encrypted image.
Hill Cipher Method
Hill cipher is an application of linear algebra
to cryptography, developed by the mathematician
Lester Hill. Image encryption using hill cipher
algorithm is derived from the work presented by
Bibhudendra
Acharya
et.al[4,5].Hill
cipher
algorithm is one of the symmetric key algorithm, it
takes n successive plaintext letters and substitutes n
cipher text letters. If switch value is ‘0’ hill cipher
with invertible matrix is performed, if switch value
is ‘1’ hill cipher with non-invertible matrix is
performed.
III. Bits rotation and Reversal
technique for image encryption
Here each pixel values of an input image is
converted into equivalent eight bit binary number.
M bits from the eight bit binary number are rotated
to right and reversed.
For example, Pin(i,j) is the pixel values of an input
image. [B1B2 B3 B5 B6 B7 B8] is equivalent eight
bit binary representation of Pin(i,j).
IV. Proposed Dual Image Encryption
Method
The above image encryption method contains three
stages. In the first stage Bits Rotation and Reversal
operation is applied to both input images. Lower
nibbles of corresponding pixels of both resultant
images are exchanged in stage two. And in stage three
Hill cipher with invertible matrix and Hill cipher with
non-invertible matrix operation depending on the
switch input value. Fig.1 shows the block diagram of
proposed Dual Image Encryption Algorithm.
Image1
Switch
Hill cipher
using Noninvertible
matrix
Image2
Hill cipher
using
invertible
matrix
Decimal to binary
i.e. Pin(i,j)
.
[B1B2 B3 B5 B6 B7 B8]
If M=5, five bits of input byte are rotated right to
generate resultant byte as [B4 B5 B6 B7 B8 B1 B2
B3].
After rotation, rotated five bits i.e. B4 B5 B6 B7 B8,
decimal
get reversed as B8 B7 B6 B5Binary
B4 toand
hence we get
the resultant byte as [B8 B7 B6 B5 B4 B1 B2
B3].This resultant byte is converted to equivalent
decimal number Pin(i,j).
[B8 B7 B6 B5 B4 B1 B2 B3]
Bit-wise Rotation by M times
Higher nibble of each corresponding
pixels of two images are exchanged
Encrypted
Image1
Encrypted
Image2
Pout(i,j)
here Pout(i,j) is the output pixel value of resultant
image.
Fig.1: Block diagram of proposed Dual Image
Encryption
Image1
Image2
A detail study has been conducted and the results
are summarized as followings. Different images have
been tested, and similar results are obtained.
1) Histogram of Encrypted Images
In order to appear random, the histograms of the
encrypted image should be uniform distributed in all
gray levels. Fig.3. shows the histograms of original
and the encrypted images. It can be observed that a
flat histogram is resulted from the encrypted image.
Fig.3: Histograms of input and output images. First shows
histograms of two input images (Cameraman.tif and lena.gif).
Second row shows, histograms of two respective encrypted
images.
2) Correlation of Adjacent Pixels
Fig.2: Input and Encrypted images. Row 1 consists of two
input images, row 2 consists of output of stage 1 and 2, row
3 consists of encrypted image using invertible matrix and
row 4 consists of encrypted image using non invertible
matrix.
v.
Results and Discussions
In this section, some security analysis of results
on the proposed approach are described, including
the most important ones like statistical analysis, and
differential analysis.
A. Statical Analysis
In order to resist the statistical attacks, the
encrypted images should possess certain random
properties.
The correlation between two vertically adjacent
pixels, two horizontally adjacent pixels in a cipher
image can be computed by using the formula
Where x and y are gray levels of two adjacent pixels in
the image. Fig.6. shows the correlations of two
adjacent pixels in the input images and in the
respective encrypted images. The correlation
coefficients of both images are computed in both
horizontal and vertical directions and tabulated in
TABLE 1. In Fig.4, correlation of adjacent pixels is
represented graphically.
TABLE I
Image Horizontal
1
Vertical
Image Horizontal
2
Vertical
Input Image
0.9863
Encrypted
Image
0.1419
0.7313
0.8580
0.0150
0.0072
0.7001
0.0018
They are Number of Pixel Change Rate
(NPCR)and Unified Average Changing Intensity
(UACI).The NPCR is used to measure the number
of pixels in difference of gray level in two images.
Let C (i, j) and C’ (i, j) be the ith row and jth
column pixel of two images C and C’, respectively,
the NPCR can be defined as
Where N is the total number of pixels in the image
and D (i, j) is defined as
Another quantity, Unified Average Changing
Intensity (UACI) measures the average intensity of
differences between the two images. It can be
defined as
Two quantities, NACP and UACI are calculates for
various images using eq. (3) and eq. (4)
respectively. The results are tabulated in the
TABLE II.
TABLE II
Fig. 4.Correlation of adjacent pixels of input and
encrypted images. Row 1 shows, horizontal &
vertical correlation of adjacent Pixels of input
image 1. Row 2 shows, horizontal& vertical
correlation of adjacent Pixels of input image
2.Row 3 & 4 show, horizontal & vertical
correlation of adjacent Pixels of respective
encrypted images.
3) Differential analysis
The major requirement of all the encryption
techniques is the encrypted image should be
greatly different from its original form. Two
measures are adopted to quantify this
requirement.
Name of Input
Image
NPCR
UACI
Cameraman
pandu
99.5987
99.7055
34.4
12.2
Along with Statistical Analysis & Differential
Analysis, Mean Square Error (MSE) , Peak Signal
to Noise Ratio (PSNR) and Image Entropy for the
proposed technique has been computed for different
images. We know that, as the MSE increases,
PSNR decreases, resulting more randomness in the
encrypted image. MSE is calculated using the
formula
References
Where, C (i, j) and C’ (i, j) be the ith row and jth
column pixel of two images C and C’,
respectively. M and N are number of rows and
columns of original image.
PSNR can be computed by
2] S.R.M.Prassana et al. “An Image Encryption
Method with Magnitude and Phase Manipulation
using Carrier Images”. IJCS,2006,Vol.1,no.2,pp.132137.
Where R is 255 as we used 8-bit image for
experiment.
Calculated results of MSE and PSNR are
tabulated in TABLE III.
TABLE III
Name of Input Image
MSE
Cameraman
Lena
105.3766
234.3521
1] Panduranga H T, Naveen kumar S K,”A novel
image encryption technique using multi wave based
carrier image” 1877-7058 © 2012 Published by
Elsevier Ltd.
PSNR
8.3628
4.8909
Image Entropy of input and encrypted images are
calculated and tabulated in TABLE IV.
3] ISMAIL I.A.1”How to repair the Hill cipher 2006
7(12):2022-2030
4] Panduranga H T, Naveen kumar S K, “Hybrid
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and Reiterative key Matrix generation Methods for
TABLE IV
Hill Cipher System”. International Journal of Recent
Input Image Encrypted Image Trends in Engineering, Vol.1, No.4, May 2009,
7.0097
7.7344
Image 1
pp.106-108
0.9658
7.9736
Image 2
7] Narendra K Pareek, “Design and analysis of a novel
Increase of entropy in encrypted images can be digital image encryption scheme”, IJNSA, Vol.4,
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entropy of encrypted image is almost equal to
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Permutation and Hill Cipher”
eight.
VI.
Conclusion
In this paper we presented an approach for
image encryption which has three stages. If we
use only Bits Rotation and Reversal only Hill
Cipher technique for images with uniform back
ground, we can predict original images. But it is
difficult predict the original images. The
performance of the proposed approach is
evaluated based on the Statistical Analysis,
Differential Analysis, MSE, PSNR and Image
Entropy. We conclude that the encrypted images
using combinational approach is more scrambled
as compare to individual technique.