Abstract:

The

current state of play in the field of encryption algorithm. A substitution technique is one of the method

in cryptography encrypting a plain text into cipher text. In particular encryption are widely used for

bulk data and link encryption. In

today’s world there are more popular and interesting substitution techniques

are currently in use. This paper focuses

mainly on the different kinds of substitution techniques. Aim an extensive experimental study of

implementation of various available substitution techniques. This study extends to the performance

parameters used in substitution processes and analyzing on their security

issues.

Keywords: substitution ,encryption, plaintext,

ciphertext.

Introduction:

The high growth in the networking

technology leads a common culture for interchanging of the data very

drastically. In substitution technique is one of the method encrypting a plain

text into cipher text. Therefore the information has to be protected while

transmitting it, Sensitive information like credit cards, banking transactions

and social security numbers and department of defense need to be protected. For

this many substitution techniques are

existing which are used to avoid the theft of information. In recent days of

wireless communication, the encryption of data plays a major role in securing

the data in online transmission focuses mainly on its security across the

wireless. Different substitution techniques are used to protect the

confidential data from unauthorized use. substitution is a very common

technique for promoting the information security. The evolution of substitution

moving towards a future of endless possibilities. This paper holds some of

those recent existing substitution techniques and their security issues.

Cryptography

Basic Terms:

·

Plain

text:

Plain text is a

original message. Any communication in

the language that we speak that is the human language, takes the form of plain

text or clear text. That is a message in

plain text can be understood by anybody knowing the language as long as the

message is not converted in any manner.

The actual message that has to be send to the receiver is given a

special name as plain text. For example,

“Hi Ramya” is a plain text and send it

to priya and priya receive the plain text message as “Hi Ramya”.

·

Cipher

text:

Cipher text is a coded message. Plain text can be encrypted as cipher text by

the help of secret key. Cipher text is

the encrypted result. Plain text can

encrypted by encryption algorithm and converted into cipher text. The message that cannot be understood by

anyone called as cipher text. In

cryptography the original message is transformed into cipher text before the

transmission of actual message. For

example, “i8&yd$y” is a cipher text produced for “Hi Ramya”.

·

Encryption:

The process of converting a

original text into cipher text are known as encryption. Encryption is used to protect sensitive

information. The encryption technique is used to send the confidential messages

through an insecure channel. The process

of encryption the required information an encryption algorithm and a key. An encryption algorithm means the technique

that has been used in encryption.

Encryption takes place at the sender side.

·

Decryption:

The reverse process of encryption is known as decryption. It is a process of converting cipher text

into plain text. Cryptography uses the

decryption technique at the receiver to obtain the original text into cipher

text. The process of decryption requires

a decryption algorithm and a key. A

decryption algorithm means the technique that has been used in decryption. Generally the encryption and decryption

algorithm are same.

Substitution

techniques:

A

substitution techniques is one in which the letters of plain text are replaced

by other letters or by numbers or symbols.

If the plaintext is viewed as a sequence of bits, then substitution

involves replacing plaintext bit patterns with cipher text bit patterns.

Types of substitution

techniques:

·

Caesar cipher

·

Mono alphabetic cipher

·

Play fair cipher

·

Hill cipher

·

Poly alphabetic cipher

Caesar cipher:

The earliest known use of a substitution cipher, and

the simplest was by Julius Caesar. The

Caesar cipher involves replacing each letter of the alphabet with the letter

standing three places further down the alphabet. The shift Caesar cipher, caesar’s code or

Caesar shift, is one of the simplest and most widely known encryption

techniques.

Plain text: MEET

ME

Cipher text: PHHW PH

Algorithm used:

C=E(3,P)=(P+3) mod 26.

A shift may be of any amount so that the general Caesar algorithm

is C=E(K,P)=(P+K) mod 26. Where k takes on a value in the range 1 to

25. The decryption algorithm is simply

P=D(K,C)=(C-K)mod

26

The

encryption and decryption algorithms are known.

There are only 25 keys to try.

The language of the plaintext is known and easily recognizable.

Mono alphabetic cipher:

There is only 25

possible keys. The Caesar cipher is far

from secure. A dramatic increase in the

key space can be achieved by allowing an arbitrary substitution.

Plain

text: a b c d e f g h i j k l m n o p q r s t u v w x y z.

Cipher

text: D E F G H I J K L M N O P Q R S T

U V W X Y Z A B C.

If instead the cipher line can be

any permutation of the 26 alphabetic characters then there are 26! Or greater

than 4*1026 possible keys.

This is 10 orders of magnitude greater than the key space for DES. Apart from single alphabet replacements, the

cryptanalyst also looks for repeated patterns of word to try the attacks. For example, the cryptanalyst might look for

two-alphabet cipher text patterns since the word to occurs very frequently in

English. If the cryptanalyst finds that

two alphabet combination are found frequently in a cipher text message. Next the cryptanalyst might try to find repeating

three-alphabet patterns and try and replace them with the word the and so on.

Playfair

cipher:

The playfair cipher,

also called as playfair square, is a cryptographic techniques that is used for

manual encryption of data. The best

known multiple-letter encryption cipher is the playfair. Which treats diagrams in the plain text as

single units and translates these units into cipher text.

P

L

A

Y

F

I

R

E

X

M

B

C

D

G

H

K

N

O

Q

S

T

U

V

W

Z

1. No repeating letters.

2. Remove the letter J.

3. Insert the desire keyword in the table.

4. Followed by the rest of the alphabet.

Hill cipher:

Another

interesting multi letter cipher is the Hill cipher, development by the

mathematician Lester Hill invented in 1929.

Hill cipher has its roots in matrix theory of mathematics. More specifically, we need to know how to

compute the inverse of a matrix. This

encryption algorithm takes m successive plaintext letters and substitutes for

the m cipher text letters. The hill cipher

is vulnerable to the known plain text.

C=KP mod 26.

Poly alphabetic cipher:

The mono alphabetic

approach is called as an poly alphabetic cipher. Leon Battista invented the polyalphabetic

substitution cipher in 1568. This cipher

has been broken many times and yet it has been used extensively. The vignere cipher and the Beaufort cipher

are examples of polyalphabetic substitution cipher. This cipher uses multiple one character

keys. Each of the keys encrypts one

plain text character. The first key

encrypts the first plain text character; the second key encrypts the second

plain text characters and so on. After

all the keys are used, they are recycled.

Thus, if we have 30 one letter keys, every 30th character in

the plain text would be replaced with the same key. This number is called as the period of the

cipher.

The

main features of polyalphabetic substitution cipher are:

1.

It uses a set of related monoalphabetic

substitution rules.

2.

It uses a key that determines which rules is

used for which transmission.

Conclusion:

In

this wireless world now a days, the security for the data has become highly

important since the communication by transmitting of digital products over the

open network occur very frequently. In this paper, it has been surveyed that

the existing works on the encryption substitution techniques. Those encryption

substitution techniques are studied and analyzed well to promote the

performance of the encryption methods also to ensure the security proceedings.

To sum up, all the techniques are useful for real-time encryption. Each

technique is unique in its own way, which might be suitable for different

applications. Everyday new encryption technique is evolving hence fast and

secure conventional encryption substitution techniques will always work out

with high rate of security.

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1. William Stallings ” Network

Security Essentials (Applications and Standards)”, Pearson Education, 2004.

2.

Turki Al-Somani ,Khalid Al-Zamil “Performance Evaluation of Three

Encryption/Decryption Algorithms on the SunOS and Linux Operating Systems”,

Theses

3. www.ijarcsse.com

4. Thambiraja,

Ramesh, Umarani. A survey on various most common encryption techniques in the

proceeding of the ijarcsse.

5. Cryptography

and network security by Atul Kahate(second edition)

6. https://learncryptography.com

7. https://www.techopedia.com