Abstract: security. The evolution of substitution moving towards


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

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Keywords:  substitution ,encryption, plaintext,



 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.

Basic Terms:


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 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”.



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.




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 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

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


Plain text:  MEET 

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


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. 


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.

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.



          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.
































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:

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

main features of polyalphabetic substitution cipher are:

 It uses a set of related monoalphabetic
substitution rules.

 It uses a key that determines which rules is
used for which transmission.  



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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