an enhanced symmetric-key block cipher algorithm to manage network security

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IPASJ International Journal of Computer Science(IIJCS)Web Site: http://www.ipasj.org/IIJCS/IIJCS.htm

A Publisher for Research Motivation ........ Email: [email protected]

Volume 3, Issue 5, May 2015 ISSN 2321-5992

Volume 3 Issue 5 May 2015 Page 58

ABSTRACT

This paper describes the cryptography and enhancement in AES cipher. An iteration of the byte sub , mix column ,shift row , add

round key steps is called a round. The dependency of the amount of rounds of the algorithm is on the key size. There is a use of S-

box creation to perform the task we discussed the enhancement in advanced encryption standard with the various parameters in this

paper. In this , a polynomial multiplication (poly-mult) function is used and we compared the various parameters like periodicity,entropy , histogram, autocorrelation, N-gram.

Keywords: Advanced Encryption Standard, plain text , cipher,polynomial multiplication, entropy, ,encryption ,decryption,

histogram.

1. INTRODUCTION

Cryptography is a Greek word that virtually means that the art of writing secrets. Practical, cryptography is that the task of

transforming data into a type that’s unintelligible, but simultaneously allows the intended recipient to retrieve the original

data using a secret key. Cryptographic algorithms (or ciphers, as they are often called) are special programs designed to

protect sensitive data on open communication links. At the time of encryption, ciphers transform the original plaintext

message into unintelligible cipher text. Decryption means that the method of retrieving plaintext from cipher text.

1.1 AES Algorithm

AES is an iterated symmetric block cipher, meaningly:

-By repeating the same defined steps multiple times AES works.

-AES is An algorithm called secret key encryption algorithm.

-On a fixed number of bytes AES operates.

AES as well as most encryption algorithms is reversible. This implies that almost the same steps are performed to complete

both encryption and decryption in reverse order. As the AES algorithm operation is done on bytes, which makes it easy to

implement and explain. This key is expanded into individual sub keys , that is for each operation round. This process is

known as KEY EXPANSION. As mentioned before AES is an iterated block cipher. That means the same operations are

performed many times on a fixed number of bytes. These operations can simpler be broken down to the following functions:ADD ROUND KEY

BYTE SUB

An Enhanced Symmetric-key block cipher

algorithm to manage network security 1Swati Kashyap , Er. Richa

2

1 Student, Haryana Engineering College,

2 lecturer, Haryana Engineering College.







SHIFT ROW

MIX COLUMN

SubByte transformation: (S-box substitution) provides non linearity and confusion, created by multiplicative inverse and

transformation.

ShiftRow: (rotations) provides inter-column diffusion wherever the bytes within the last three rows of the states arecyclically shifted.

MixColumn: (linear combination) provides inter-byte diffusion wherever every column vector is multiplied by a fixed

matrix. The bytes are considered as polynomials instead of numbers.

AddRoundKey: (means that round key bytes XOR with every byte of the state and the round key) provides confusion .

Histogram

It represents the frequency distribution of individual characters of document. The horizontal axis that is x-axis of the

histogram contains all the characters in the character set: In a text window the character set contains the letters of the

alphabet selected in Text Options, whereas in a window for hexadecimal inputs and outputs , the numbers 0 -255 contained

by the character set .The each character frequency is shown (as a percentage) on the vertical axis.

Autocorrelation

Autocorrelation means that a text is compared to shifted copies of the same text. From both texts the characters that match

one another in such a comparison, are examined. Thus, it is possible to crack the Vigenère cipher. Repeatedly repeatingmaximum values of matching characters indicate the key length of the Vigenère cipher.The autocorrelation analysis is more

efficient and clearer than the Friedman or Kasiski test. The versatile analysis is their and can also be used for example in

signal processing. A frequency analysis is a complex calculation and thus it is advisable to use locally installed tools such as

CrypTool for large texts.

Entropy

The entropy of a document is an index of its information content. The calculation of entropy is done in bits per character.

From the information theory point of view, in the current window the data can be viewed as a message source. To calculate

the information content one examines the probability distribution of this source. Here ,It is supposed as that the individual

messages (characters in the document / file) are stochastically independent of each other and are transmitted by the source

with a uniform probability.

The content information of M[i] that is a message is defined by Information content (M[i]):= log(1/p[i]) = -log(p[i])

Where message M[i] is transmitted by the message source and p[i] (probability) and log denotes logarithms to base 2 (asindeed it does elsewhere in this document).

1.2 MATLAB

MATLAB is widely used in all areas of applied mathematics, in research and education at industry, and in the universities.

MATLAB describes as MATrix LABoratory and the software is built up around vectors and matrices. Particularly this

makes the software useful for linear algebra but MATLAB is also a great tool for solving algebraic and differential

equations and for numerical integration. It has powerful graphic tools and can produce nice pictures in both 2D and 3D. It

is also called as a programming language, and for writing mathematical programs, it is one of the easiest programming

languages. MATLAB has some tool boxes useful for optimization , signal processing, image processing etc.

MATLAB is case sensitive. This means that MATLAB knows a difference between letters written as

lower and upper case letters. Like , in MATLAB sin(2) will be understood but Sin(2) will not be

understood .

Variables in MATLABWe can easily define our own variables in MATLAB. Suppose we need to use the value of ,instead of

typing 3.5*sin(2.9)over and over again, 3.5sin(2.9) repeatedly. we can denote this variable as x by typing the following:

x=3.5*sin(2.9)

(Please try this in MATLAB.) Now type

x+1

and observe what happens. Note that we did not need to declare x as a variable that is supposed to hold a floating point

number as we would need to do in most programming languages.

Often, we may not want to have the result of a calculation printed-out to the command window. To crush this output, we puta semi-colon at the end of the command; In "the background” MATLAB still performs the command . If you defined x as

above, now type







y=2*x;

y

and observe what happened.

In many cases we want to know what variables we have declared. By typing whos ,we can do this. Alternatively, by

openning the "Workspace" window, values can be viewed. By selecting the Workspace option from the View menu this can

be done. Type clear if you want to erase all variables from the MATLAB memory. To erase a specific variable , x ,

type clear x. To clear two specific variables, say x and y, type clear x y, that is separate the different variables with a space.

By selecting them in the Workspace window and selecting the delete option ,Variables can be cleared.

1.3 CRYPTOOL

CrypTool is a freeware and open source program which enables you to apply and analyze cryptographic mechanisms.

CrypTool contains extensive online help, that can be known without exhaustive knowledge of cryptography. CrypTool has

been developed continuously since 1998 . It is available in German, English, Polish, Spanish and Serbian. CrypTool has

implemented almost all state-of-the-art crypto functions and allows you to learn about and use cryptography within the same

environment. For obtaining the key starting from knowledge of the encrypted document and any additional information (theunencrypted document or the language of the document) , Automatic analysis tools are allowing that for the classic

encryption algorithms. To support your own analysis of documents, CrypTool can display a histogram of the document,

determine the statistics for any n-grams and calculate entropy and autocorrelation.

2. RELATED WORK

Bahar Saini [1] , AES algorithm is considered as a secured algorithm. Still, some issues like security lie in the S-box and

key used In this, their is focus on the S-box rotation so that information become highly secured .As the standard AES

consists of four stages while in the new design, there is five stages The extra stage is known as S-box rotation

.Implementation of proposed work and Experimental results are to be discuss here.

A.E.Rohiem, F.M.Ahmed and A.M.Mustafa [2],In this paper, a novel method of using customized (AES) variable

parameters is introduced. This method depends on a continuous parameters reconfiguration and a customization of each

internal block. The customization depends on varying the four transformations (polynomial and affine transformations forS-Box (SB), ShiftRows (SR) transformation, and MixColumn (MC) transformation). Internal AES blocks (SB, SR, and

MC) are varied each round. Further more, these blocks are randomly interconnected during

each session. The ciphered output was tested using avalanche, strict avalanche, and other NIST tests. This method

overcomes (ECB) mode problems which appear when there is high redundancy in the plain data and also increasing

strength against brute force attacks. The proposed AES is implemented on Field programmable Gate Arrays (FPGAs).

Alan Kaminsky, Michael Kurdziel, Stanislaw Radziszowski [3], Since its release in November 2001, the Advanced

Encryption Standard (NIST FIPS-197) has been the subject of extensive cryptanalysis research. This research importance

has intensified since AES was named, by NSA as a Type-1 Suite B Encryption Algorithm (CNSSP-15) in 2003. As such,

AES is now authorized to protect classified and unclassified national security systems and information. An overview of

current cryptanalysis research on the AES cryptographic algorithm is provided by this paper. Discussion is given on the

impact by each technique to the strength of the algorithm in national security applications. The conclusion of this paper is

with an attempt at a forecast of the usable life of AES in these applications.

Amritpal Singh, Mohit Marwaha, Sandeep Singh ,Baljinder Singh[4], In today world importance of exchange of data over

internet and other media type is eminent; the search for best data protection against security attacks and a method to timely

deliver the data without much delay is the matter of discussion among security related communities. Cryptography is a

method that provides the security mechanism in timely driven fashion. The 2 main quality that identify and differentiate

encryption algorithm from another are their capability to secure the protected data against attacks and their speed and

effectiveness in securing the data. A comparative study between four such widely used encryption algorithms RSA, DES,

3DES and AES is provided by this paper on the basis of their ability to secure and protect data against attacks and speed of

encryption and decryption

PROPOSED WORK

In this paper , we have done the enhancement in AES cipher that is advanced encryption cipher by using the poly mult

function. A cipher text is produce by applying poly mult function in MATLAB. The cipher and the inverse cipher text is

produce by applying the aes rounds in MATLAB. As shown below in the figures.







Figure 1: cipher

Figure 2: inverse cipher

key_hex = {'2b' '7e' '15' '16' '28' 'ae' 'd2' 'a6' 'ab' 'f7' '15' '88' '09' 'cf' '4f' '3c'};

plaintext_hex = {'22' '33' '44' '55' '66' '77' '88' '99' 'ab' 'ba' 'aa' 'bb' 'ac' 'ad' 'ae' 'af'};

Compared AES cipher

Figure 3: cipher of compared AES

Figure 4: inverse cipher of compared AES

2.1 RESULTS AND DISCUSSION

Here we firstly shows the results of cipher having parameters histogram ,autocorrelation.







Histogram –

Figure 5: histogram of enhanced AES

Figure 6: histogram of compared AES

So, in enhanced AES cipher we got the repeated character less as compare to the old AES cipher as shown in the figures. In

old cipher the repeated character is four having frequency greater than 20 but in enhanced cipher the two repeated character

is present and having frequency greater 20.

Autocorrelation-

Figure 7: autocorrelation of enhanced AES

Figure 8: autocorrelation of compared AES






Volume 3 Issue 5 May 2015 3

In this autocorrelation ,the number of characters that match is less in enhanced cipher. Now showing the result of inverse

cipher with the parameters entropy, histogram.

Figure 9: histogram of enhanced AES.

FIGURE 10: histogram of compared AES.

In histogram the enhanced AES cipher have 38 frequency at maximum where as in compared AES the frequency is 41.

Entropy

Figure 11: Entropy of enhanced AES.







figure 12: Entropy of compared AES.

In this , the entropy of enhanced AES is greater than the compared AES . figures shows the result.

Table 1 : shows comparision for enhanced AES cipher

parameters Enhanced AES

cipher

Compared

AES cipher

Autocorrelation High Less

Histogram Frequency is

maintained

Not

maintained

N-Gram 2 characters

more than 20

4 characters

more than 20

Periodicity no no

Table 2 : shows comparision for enhanced AES inverse cipher

parameters Enhanced AES

cipher

Compared

AES cipher

Autocorrelation High Less

Histogram Frequency is

maintained

Not

maintained

N-Gram 2 characters

more than 20

4 characters

more than 20

Periodicity no no

3.CONCLUSIONS

We conclude our result paper as we have done the comparision of enhanced AES cipher with the parameters like histogram,

n-garm , autocorrelation , entropy . so we achieved our goal as we got higher entropy and histogram in inverse cipher and

higher histogram and autocorrelation in cipher in comparision with the old AES cipher. The results shows that the

enhanced AES cipher is better and improved entropy , autocorrelation and histogram than the old cipher.

References[1].

Bahar Saini,” Implementation of AES using S-BOX rotation”, International journal of advanced research in

computer science and software engineering, May 2014.







[2].

A.E.Rohiem, F.M.Ahmed and A.M.Mustafa, “FPGA Implementation of reconfigurable parameters AES algorithm”,

13th international conference on AEROSPACESCIENCE AND AVIATION TECHNOLOGY, ASAT-13, May 26-29,

2009.

[3].

Alan Kaminsky, Michael Kurdziel, Stanislaw Radziszowski,”An overview of cryptanalysis research for the advanced

encryption standard”, Rochester institute of Technology , NY,Horris corp, RF communication Div.,Rochester,NY.[4].

Amritpal Singh, Mohit Marwaha, Baljinder Singh, Sandeep Singh,” Comparative study of DES, 3DES, AES and

RSA”.

[5].

Eltayeb Salih Abuelyman, and Mohamed Ahmed El-Affendi, An Optimized Real Time Generation of S-Box Inverses

Using Arithmetic Modulo Powers of Two, IJCSNS International Journal of Computer Science and Network Security,

VOL.7 No.12, December 2007

[6].

Ming-Haw Jing, Zih-Heng Chen, Jian-Hong Chen, Yan-Haw Chen, Reconfigurable system for high-speed and

diversified AES using FPGA, Microprocessors and Microsystems 31 (2007) 94–102.

AUTHOR

Swati received the B.tech. degree in computer Engineering from Haryana engineering college in 2013

an enhanced symmetric-key block cipher algorithm to manage network security

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