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A Competitive Study of Cryptography Techniques over Block Cipher

Ashwak M. AL-Abiachi, Faudziah Ahmad, Ku Ruhana

Information Technology Department, University Utara Malaysia, 06010, Sintok, Malaysia

ashwakalabaichi2007@yahoo.com, fudz@uum.edu.my, ruhana@uum.edu.my

Abstract—The complexity of cryptography does not allow

many people to actually understand the motivations and

therefore available for practicing security cryptography.

Cryptography process seeks to distribute an estimation of

basic cryptographic primitives across a number of

confluences in order to reduce security assumptions on

individual nodes, which establish a level of fault-tolerance

opposing to the node alteration. In a progressively networked

and distributed communications environment, there are more

and more useful situations where the ability to distribute a

computation between a number of unlike network

intersections is needed. The reason back to the efficiency

(separate nodes perform distinct tasks), fault-tolerance (if

some nodes are unavailable then others can perform the task)

and security (the trust required to perform the task is shared

between nodes) that order differently. Hence, this paper aims

to describe and review the different research that has done

toward text encryption and description in the block cipher.

Moreover, this paper suggests a cryptography model in the

block cipher.

Keywords: Cryptography, text encryption, block cipher, AES

I.

INTRODUCTION

Unclassified nature of the algorithm cannot be stressed

enough. However, by publishing the algorithm, it gives the

cryptographer choices to be seen by a wide range of

academic cryptography, keen to break into the system to

publish articles demonstrating how smart they are. The real

secret is that the key and its length are very important,

considering a simple combination is safer. The general

principle is that figures are inserted in sequence and the key

is secret. A key length of two digit means that there are 100

possibilities. A three-digit key length is 1000 possibilities

and a key length of six figures means a million. As longer

the key is, with greater workload (work factor) that the

cryptanalyst has to do. Work factor to break the system by

the exhaustive search in the digit space is exponential in

relation to the key length [1]. The secret comes from

having a strong algorithm (but public) and a long key. To

prevent the younger brother to read other mail, there are

enough 64-bit keys. To keep at distance powerful enemies

the needed are at least 256 bits keys [2].

Encryption methods have historically been divided into

two categories: substitution ciphers and transposition

ciphers. Stallings had explained each of these ciphers as

essential information for

cryptography [3].

An example of encryption algorithms is AES (Rijndael)

which identifies as a symmetric algorithm. This means that

the encryption key can be calculated from the

corresponding decryption and vice versa [4]. Security an

algorithm based on symmetric key, which must be remains

secret [5]. The AES block cipher as acting in plaintext in

groups of each bit time which are called blocks [6]. Typical

understanding modern

size of a block is 64 bits. Each round transformation

consists of three separate transformations called layers:

?

Linear mixing layer;

?

Non-linear layer;

?

Key addition layer.

Before the first round of AES processing algorithms, a

key addition layer takes place. The linear mixing layer of

the final round is different than the other rounds. Each

round of treatment consists

transformations that compose 3 layers [7].

However, AES is an iterative algorithm with variable

size block processing and key which can be 128, 192 or

256 bits. The interim results of the algorithm after each

transformation called State [8]. Each State is expressed as a

rectangular table of data bytes [9]. The table blow has 4

rows, while the number of batteries (NB) is the size of the

block processing divided by 32. Similarly, the encryption

key (cipher key) expressed as rectangular table with data

bytes. The table has 4 rows and number of columns [10] is

the key length divided by 32. Each table element is one

byte.

of four different

Table1: State (with Nb = 6) and encryption key (with Nk =

4)

Round

ShiftRow

AddRoundKey (State, RoundKey);}The final round

is defined as follows:

FinalRound (State, RoundKey) {{ByteSub (State);

ShiftRow (State); AddRoundKey

RoundKey);}

(State, RoundKey)

(State);

{ByteSub (State);

(State); MixColumn

(State,

2011 UKSim 13th International Conference on Modelling and Simulation

978-0-7695-4376-5/11 $26.00 © 2011 IEEE

DOI 10.1109/UKSIM.2011.85

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Moreover, each column is referred as "word" or "4-byte

vector". Each table can be considered as one-dimensional

table of elements "4-byte vectors". The entrance and exit of

AES can be regarded as dimensional data tables with 8-bit

(byte) numbered from 4 * Nb-1. Similarly, the key

numbered 0 to 4 * Nk-1. H entrance cipher (plaintext) is

shown in bytes of the table with the State series:

The number of laps made by the algorithm denoted by

Nr and depends on the values Nb and Nk as shown in table

1.

Table 2: The values of Nr, Nb, Nk

A block cipher cryptosystem consists of two algorithms,

the encryption algorithm and decryption algorithm that are

illustrated in Figure 1. The encryption algorithm takes as

input an n-bit plaintext M and a k-bit key K and outputs an

n-bit ciphertext C; the decryption algorithm takes as input

an n-bit ciphertext C and a k-bit key K and outputs an n-bit

plaintext M [11]. For any fixed key, the decryption

algorithm acts as the inverse process of the encryption

algorithm as in following equation (1.1), (1.2).

C=Ek(M) (1.3)

M=Dk (C) =E-1(Ek(M)) (1.4)

The block cipher breaks M into successive blocks M1,

M2, and enciphers each M1 with the same key K; that is as

in equation (1.5).

Ek(M)=Ek(M1) Ek(M2) (1.5)

Typically, each block is several characters long. Two

important block ciphers classes are substitution and

transposition ciphers. Simple substitution and homophonic

substitution ciphers are blocks ciphers even thought the

unit of encryption is a single character. This is due to the

same key being used for each character [12].

Figure 1: The encryption and decryption operations in

block cipher algorithm (ref…)

Several groups of researchers that have analyzed

some of the block algorithms already found a way to

determine their strength or weakness. Apparently, there are

some properties that determine the block algorithms

strength or weakness.

? Complementation

The complexity of a brute-force attack is reduced factor

of two by using this complementation property. The simple

relation can be defined by the following rule IF Ek (P) = C

THEN EK’ (P’) = C' P’, C’, and K' are the bit-wise

complements of P, C and K [13].

There are no simple relations in a high-quality block

cipher. Weaknesses in the block cipher are created by this

property. An example that has this property is the DES

algorithm.

? The Strict Avalanche Criteria (SAC)

The avalanche effect is a property that seems to be very

important: it deals with the number of S-Box output bits

change when the subsets of the inputs bits are changed.

Conditions can be easily imposed on the Boolean

function to satisfy particular avalanche criteria but the

difficult task is constructing them [14].

SAC guarantees that exactly half of the output bits

change when one input bit is changed [15].

II.

EXISTING ISSUES

Generally, the utilization of the encryption techniques

has raises different security issues, which consisted mostly

on how to effectively manage the encryption keys to ensure

that they are safeguarded throughout their life cycle and are

protected from unauthorized disclosure and modification.

a0,0, a1,0, a2,0, a3,0, a0,1,a1,1, a2,1, a3,1, a4,1, … (1)

*While byte key shown in the table key in the order:

k 0,0, k 1,0, k 2,0, k 3,0, k 0,1, k 1,1, k 2,1, k 3,1, k 4,1, ....(2)

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Encryption keys are a sequence of symbols used with a

cryptographic algorithm, which enables encryption and

decryption. It is imperative that an efficient key

management program be established and facilitated

throughout public safety agencies. Key management

ensures that critical and sensitive radio transmissions are

protected with proper encryption methods and that

encryption keys are controlled and securely stored during

their life cycle. For purposes of this report, encryption is

defined as the process of transforming plain text into

unintelligible form by using a cryptographic system. The

cryptosystem is hardware and software providing the

means to encrypt and decrypt transmissions. Figure 2

presents a basic encryption concept.

The basic meteorological of encryption comprise the

algorithm (i.e., a mode of changing information), the key

(i.e., a secret introducing point for the algorithm), and the

key authority (i.e., key management). The key is

characteristically recognized as a binary number used with

a cryptographic algorithm to authorize the encryption and

decryption of information over the block cipher. The key

jurisdictions the algorithmic alteration executed to

information transmission during encryption and description

process that must be anticipated so that a corresponding

decryption algorithm can backtrack the operation by

employing a suitable key. Several reasons in the encryption

of information over block cipher are observed in terms

of key management, which known as an important issue to

the public safety community, most of these issues

addressed the following:

?

Difficulties in addressing the security issues

regarding encryption key management;

?

Lacks in providing a suitable details about the

different threats in terms of decision makers on

the importance of key management;

?

Difficulties in

recommendations for establishing proper key

management.

generating the suitable

Figure 2: Basic Encryption Concept

III.

RELATED WORKS

Chan & Fekri develooped a new private key

cryptosystem based on the finite-field wavelet. The

encryption and decryption are performed by the synthesis

and analysis banks of the nonlinear finite-field wavelet

transform whose filter coefficients are determined by the

keys of the users. Authors illustrate the polyphone

representation of the wavelets to introduce a shared key

mechanism for the wavelet cryptosystem. As well as adopt

the wavelets that operate over GF (256) and a nonlinear

device that performs a mapping on the field elements to

their inverse in the field. The block cipher system has a key

length of 16 symbols (128 bits) and an input block size of

30 symbols (240 bits). To evaluate the efficiency of the

developed two-round wavelet cryptographic scheme, the

study also has compared with DES and AES. The results

indicated that the wavelet cryptosystem has comparable

computational complexity to AES and approximately half

the complexity of DES. The security is tied to the length of

the wavelet basis function and to the nonlinearity within

the wavelet transform. Finally, Chan & Fekri conclude that

the lowest complexity of any of these attacks is greater than

an exhaustive key search [11].

Another study by Mousa & Hamad invistigates the

analysis process of the effect of different parameters of the

RC4 encryption algorithm that was performed to illustrate

the performance of RC4 algorithm based on changing some

of these parameters. Mousa & Hamad examined the

execution time as a function of the encryption key length

and the file size, which recognized as a complexity and

security. Meanwhile, the study demonstrated a different

data types and the role of the data type. The results have

been analyzed and interpreted as mathematical equations

showing the relationship between the examined data and

hence can be used to predict any future performance of the

algorithm under different conditions. The order of the

polynomial to approximate the execution time was justified

[16].

Additionally, Ray & Das, descirbed the Cellular

Automata [5] as a computing model of complex System

using simple rule. Ray & Das highlights the main issues in

the space, which divided into number of cell and each cell

can be one or several final state. Cells are affected by

neighbors with the application of simple rule. Furthermore,

the study deals with the Cellular Automata in cryptography

for a class of Block Ciphers through a new block

encryption algorithm based on programmable cellular

automata. The proposed algorithm belongs to the class of

symmetric key systems [17].

IV.

PROPOSED MODEL

Sequentially, providing a secure and flexible cryptography

mechanism raises the needs for analyzing and comparing

different encryption algorithms for the aim of enhancing

the security during the encryption process. Hence, this

paper suggested a cryptography mechanism in the block

cipher by managing the keys sequentially, which classified

into encryption-secret-key, description-secret-key,

shared-secret-key. These keys will works dependently for

extracting and generating the content relation to be

and

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managed later by the key management that helps to

communicate and share sensitive information. In particular,

the importance of thorough, consistent key management

processes among public safety agencies with interoperable

functions cannot be overstated. This model aims to secure

dissemination, loading, saving, and eliminating faults of

keys to make encryption implementations effective. There

are inherent possibilities if suitable key management

processes are not accompanied because of the intricacy of

dispensing keys to all block in a certain fashion. This risk

can be meaningfully appeased through sufficient key

controls and proper education on encryption key

management.

g

Figure 3: Cryptography Model over Block Cipher

V.

EXPECTED BENEFITS

The suggested cryptography model for block cipher will be

expected to:

?

Obtain a high security during the encryption and

decryption process of the text contents;

?

Simplify the management process of keys;

?

Justify and eliminate faults and other relevant

errors during the encryption process.

VI.

CONCLUSION

Cryptography can be a technology that develops, but as

long as security is made by man, cryptography is as good

as the practice of people who uses it. This paper focused on

the different security issues for providing a secure and

effective cryptography technique over the block cipher.

Most of these issues occurred when users leave keys

unattended, keys that were chosen were easy to remember

or maintain the same keys for years. This can be resolved

by the suggested model, using the encrypting key that

existed independently as an external tool by managing keys

sequentially.

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