 Open Access
 Total Downloads : 439
 Authors : Miss.Amrita Singh, Miss.Laxmi Goswami, Aijaz Ur Rahman Khan
 Paper ID : IJERTV2IS90975
 Volume & Issue : Volume 02, Issue 09 (September 2013)
 Published (First Online): 27092013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
A Novel Image ENCRYTION Algorithm for Enhanced Security
Miss.Amrita Singh, 
Miss.Laxmi Goswami 
Aijaz Ur Rahman Khan 
Asst. Professor 
Asst. Professor 
Asst.Professor 
Dr.C.V.Raman University 
Dr.C.V.Raman University 
M.M.College of Technology 
Bilaspur (C.G.) 
Bilaspur (C.G.) 
Raipur(C.G.) 
AbstractThe main aim of this paper is to develop a novel encryption algorithm for increasing the security of encryption so that only the intended person is able to decrypt the image. In this algorithm, original image is first encrypted using SCAN based encryption operation followed by ElGamel based encryption method. Various analysis has been done to test the performance of proposed algorithm.
Keywords : Image encryption, SCAN , Spiral, Orthogonal, Diagonal, Raster, MSE.

INTRODUCTION
The advancement in communication and internet technology has given a quick and fast mode of communication using world wide web. Though this mode of information interchange is very fast but at the same it also creates security problem. Encryption is one way of ensuring the security in text, image, audio and video data. Image encryption play very important role in telemedicine, medical imaging, military communication,multimedia system. Various image encryption method has been proposed by different researcher in the past which include chaosbased image encryption method[1],SCANlanguage based encryption method[25],tree structurebased encryption
method[6] and some other method[79].Some methods provides better security while other method are very efficient in term of speed. In any kind of public key crypto system, security depends on the difficulty of factoring. In 1985 [10],[11] ElGamel proposed an encryption method whose security depends on the difficulty of computing the discrete algorithms. His method of encryption require a large prime number p and its primitive root r.High level of security is ensured by using big key size[12] because big size key require a very extensive computation and hence more difficult to decrypt[13].In this paper an effort has been made to design a novel and more secure method of encryption by combining two different methods.
The proposed encryption method starts by rearranging the image pixel. In this method pixel rearrangement is carried out by different scan pattern using SCAN methodology. Scanning pattern of an image is simply a arrangement order of a pixel. Since different scan pattern has different arrangement order therefore it can be used for encryption by
generating a large number of scan pattern .Once the image is encrypted using SCAN based methodology then it is again encrypted using elgamel encryption method to enhance the security of encryption. Since ElGamel encryption method provides good security and least complexity therefore it is chosen along with the SCAN based methodology.

SCANNING METHOD
SCAN [25] is a formal language based method of accessing or arranging the position of pixels in an image.Using SCAN language,large number of scanning path can be generated. SCAN is actually a group of formal language and can be termed as Simple SCAN, Generalized SCAN, Extended SCAN. Each SCAN language follows some basic rules and grammer. There are some basic pattern of scanning and rule in each SCAN language which are used to generate some simple scanning pattern which later on can be used to generate complex scan pattern. In this proposed method four basic scan pattern has been used which are known as continuous diagonal(D),continuous raster(C),con tinuous orthogonal(O), spiral(S).Each of these basic pattern can have eight different transformations which can be numbered from 0 to 7.Transformation 0,2,4,6 are the reverse transformation of 1,3,5,7.Different types of basic scanning pattern[16] is shown in figure
(a) (b)
(c) (d)
Figure 2 (a) Spiral (b) Raster
(c) Diagonal (d) Orthogonal
We can apply each of these basic pattern individually in single image or alternatively divide the image into different parts and apply these basic pattern in different parts.
A. Partition Pattern
Partition pattern define the order by which each subregions of the image are scanned and these partition order are denoted by letter A,B, C and
E. Each partition order can also have six different transformations or pattern.
Figure 3 Partition order for
different letter
Here letter A represent the partition order which starts from left upper (denoted by 1). And goes to the rest of the three part in 6 different ways or in other words has 6 different transformation.
Figure 4 Partition pattern for A
B. Key Generation
In order to generate a key for this encryption and decryption we encode all the scanning pattern and its eighttransformation as C1C8(for continuous raster), D1D8(for Diagonal),O1O8( for orthogonal),S1S8(for Spiral).
Figure 5 SCAN Pattern Diagram
In a similar way in this method,4 different partition order (A,B,E,X) and its six transformation are being used therefore it can be encoded as A1A6,B1B6,E1E6,X1X6.
For example the key for following figure is shown below
Figure 6 Encryption Key Generation

ELGAMEL ENCRYPTION
This method is based on the facts that if p is a large prime number then the primitive root of this number p is a number r which satisfy the following property
R (mod p) r2(mod p)r2(mod p) .
rp1(mod p) 0 (1)

mod of p taken over the power of number r yield distinct and nonzero number and all are also relative prime to p. For example consider a prime number 7.The primitive root can be any integer number from 1 to 6 which satisfy the equation (1).From the table it is clear that only number 3 and 5 satisfy the equation (1) and hence these number are primitive root of prime number 7.
Figure 7


PROCEDURE FOR ELGAMEL METHOD
In this method a user has to choose the private key on the basis of which, a public key is calculated. Let p be a prime number of large value and be the primitive root of p.Suppose the selected private key is represented by r then the public key is computed by
=r (mod p) .(2)
Choose any random integer and compute b by b=k (mod p) ..(3)
If the plain text is T then compute cipher text by C=kT (mod p) ..(4)
Now, for decryption at the receiver side can be computed by
T = Cbr(mod p) ..(5)
This is due to the fact that
C br = k T (k)r
= (r )k T (k)r
= rk T rk
= T (6)
Algorithm steps for ELGamel method are as follows

Encrytion Process
Step 1 First of all choose any large prime number p
Step 2 Compute the primitive root of p and choose any one primitive root .
Step 3 Select a private key a and compute the corresponding public key using equation 2.
Step 4 Take the first pixel of the Red channel and encrypt it using equation 4 for a selected random number k
Step 5 Repeat step 4 for the pixel of Green channel.
Step 6 Repeat step 4 for the pixel of blue channel.
Step 7 Repeat step 3 to 6 till all the pixel gets encrypted.
Step 8 Merge all encrypted Red, Green and Blue pixel to get the encrypted image.
A. Decrytion Process
Step 1 Get the encrypted image and separate the Red, Gree and Blue channel.
Step 2 Compute the value of b using equation 3.
Step 3Take the first encrypted pixel of Red channel and decrypt it using equation 5.
Step 4 Repeat step 4 for Green and Blue channel.
Step 5 Merge all the decrypted Red, Green and Blue pixel to get back the decrypted image.


PROPOSED METHOD
Proposed encryption process consists of two part.The first part encrypt the original image using scanning technique as describe in the part II.Scanning technique works by changing the pixel position only. The value of each pixel remain intact. In the second part the encrypted image obtained by the first part is again encrypted using Elgamel method as described in part IV.

Encrytion Process
Encryption process is summarized as

Get the Original Image.

Encrypt the Image by applying SCAN method as describe in part II and generate the key1.

The encrypted image obtained after step 2 is again encrypted by applying ELgamel method as described in part IV and using key2.
The whole process of encryption is shown in Figure 8
Figure 8 Encryption Process


Decrytion Process
Since in this method two key are used one for scanning based method of image encryption and
another is for ELGamel method ,therefore the security of this method gets enhanced manifold.In order to decrypt the image, person must know both the keys which is difficult in this algorithm.
The decrytion process is summarized as –

Get the Encrypted image

Perform the Elgamel decryption operation using key2.

Perform the SCAN based decryption operation using key1 to get back the original image.
The decryption process is shown in figure 9



EXPERIMENTAL RESULT Proposed method is implemented in the computer having dual core processor and 2GB
RAM.In order to evaluate the performance of proposed method, Mean square error has been computed for testing the distortion between original image and decrypted image. Execution time for this algorithm is also computed and tabulated in Table 1From the Table 1 and figure 10 it is clear that the proposed method is fast and produce no distortion in decrypted image and at the same it also give enhanced security because of using two different keys for decryption.
Figure 9 Decryption Process
TABLE 1:Execution time,MSE Between Original and Decrypted Image
Image 
Image size 
MSE between Original and Decrypted Image (For Lenna Image) 
Execution Time (in second) 
Peppers.png 
256×256 
0.00 
0.30 
Peppers.png 
512×512 
0.00 
0.35 
Football.jpg 
256×256 
0.00 
0.29 
Football.jpg 
512×512 
0.00 
0.33 
Kids.jpg 
256×256 
0.00 
0.30 
Kids.jpg 
512×512 
0.00 
0.34 

(b)
(c) (d)
(a) (b)
(c) (d)
(a) (b)
(a) (b)
Figure 10 (a) original image (b)Image encrypted using SCAN method (c)Image Encrypted using ELGmel method (d) Dcrypted Image
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