Abstract: security. The evolution of substitution moving towards

Abstract:                                                                    Thecurrent state of play in the field of encryption algorithm.

  A substitution technique is one of the methodin cryptography encrypting a plain text into cipher text.  In particular encryption are widely used forbulk data and link encryption.  Intoday’s world there are more popular and interesting substitution techniquesare currently in use.  This paper focusesmainly on the different kinds of substitution techniques.  Aim an extensive experimental study ofimplementation of various available substitution techniques.  This study extends to the performanceparameters used in substitution processes and analyzing on their securityissues.

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Keywords:  substitution ,encryption, plaintext,ciphertext.Introduction:      The high growth in the networkingtechnology leads a common culture for interchanging of the data verydrastically. In substitution technique is one of the method encrypting a plaintext into cipher text. Therefore the information has to be protected whiletransmitting it, Sensitive information like credit cards, banking transactionsand social security numbers and department of defense need to be protected.

Forthis many substitution  techniques areexisting which are used to avoid the theft of information. In recent days ofwireless communication, the encryption of data plays a major role in securingthe data in online transmission focuses mainly on its security across thewireless. Different substitution techniques are used to protect theconfidential data from unauthorized use. substitution is a very commontechnique for promoting the information security. The evolution of substitutionmoving towards a future of endless possibilities. This paper holds some ofthose recent existing substitution techniques and their security issues.

CryptographyBasic Terms:·        Plaintext:Plain text is aoriginal message.  Any communication inthe language that we speak that is the human language, takes the form of plaintext or clear text.  That is a message inplain text can be understood by anybody knowing the language as long as themessage is not converted in any manner.  The actual message that has to be send to the receiver is given aspecial name as plain text.  For example,”Hi Ramya” is a plain text  and send itto priya and priya receive the plain text message as “Hi Ramya”. ·        Ciphertext:  Cipher text is a coded message.  Plain text can be encrypted as cipher text bythe help of secret key.  Cipher text isthe encrypted result.

  Plain text canencrypted by encryption algorithm and converted into cipher text.  The message that cannot be understood byanyone called as cipher text.  Incryptography the original message is transformed into cipher text before thetransmission of actual message.  Forexample, “i8&yd$y” is a cipher text produced for “Hi Ramya”. ·        Encryption:The process of converting aoriginal text into cipher text are known as encryption.  Encryption is used to protect sensitiveinformation. The encryption technique is used to send the confidential messagesthrough an insecure channel.  The processof encryption the required information an encryption algorithm and a key.

  An encryption algorithm means the techniquethat 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 textinto plain text.

  Cryptography uses thedecryption technique at the receiver to obtain the original text into ciphertext.  The process of decryption requiresa decryption algorithm and a key.  Adecryption algorithm means the technique that has been used in decryption.  Generally the encryption and decryptionalgorithm are same. Substitutiontechniques:            Asubstitution techniques is one in which the letters of plain text are replacedby other letters or by numbers or symbols.

 If the plaintext is viewed as a sequence of bits, then substitutioninvolves replacing plaintext bit patterns with cipher text bit patterns. Types of substitutiontechniques:·        Caesar cipher·        Mono alphabetic cipher·        Play fair cipher·        Hill cipher·        Poly alphabetic cipher  Caesar cipher:The earliest known use of a substitution cipher, andthe simplest was by Julius Caesar.  TheCaesar cipher involves replacing each letter of the alphabet with the letterstanding three places further down the alphabet.  The shift Caesar cipher, caesar’s code orCaesar shift, is one of the simplest and most widely known encryptiontechniques. Plain text:  MEET MECipher 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 algorithmis  C=E(K,P)=(P+K) mod 26.  Where k takes on a value in the range 1 to25.

  The decryption algorithm is simply P=D(K,C)=(C-K)mod26Theencryption 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 25possible keys.

  The Caesar cipher is farfrom secure.  A dramatic increase in thekey space can be achieved by allowing an arbitrary substitution.   Plaintext:  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.Ciphertext:  D E F G H I J K L M N O P Q R S TU V W X Y Z A B C.            If instead the cipher line can beany permutation of the 26 alphabetic characters then there are 26! Or greaterthan 4*1026 possible keys.

 This is 10 orders of magnitude greater than the key space for DES.  Apart from single alphabet replacements, thecryptanalyst also looks for repeated patterns of word to try the attacks.  For example, the cryptanalyst might look fortwo-alphabet cipher text patterns since the word to occurs very frequently inEnglish.  If the cryptanalyst finds thattwo alphabet combination are found frequently in a cipher text message.  Next the cryptanalyst might try to find repeatingthree-alphabet patterns and try and replace them with the word the and so on.

  Playfaircipher:          The playfair cipher,also called as playfair square, is a cryptographic techniques that is used formanual encryption of data.  The bestknown multiple-letter encryption cipher is the playfair.  Which treats diagrams in the plain text assingle 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: Anotherinteresting multi letter cipher is the Hill cipher, development by themathematician Lester Hill invented in 1929. Hill cipher has its roots in matrix theory of mathematics.  More specifically, we need to know how tocompute the inverse of a matrix.

  Thisencryption algorithm takes m successive plaintext letters and substitutes forthe m cipher text letters.  The hill cipheris vulnerable to the known plain text.          C=KP mod 26.      Poly alphabetic cipher:           The mono alphabeticapproach is called as an poly alphabetic cipher.  Leon Battista invented the polyalphabeticsubstitution cipher in 1568.  This cipherhas been broken many times and yet it has been used extensively.  The vignere cipher and the Beaufort cipherare examples of polyalphabetic substitution cipher.

  This cipher uses multiple one characterkeys.  Each of the keys encrypts oneplain text character.  The first keyencrypts the first plain text character; the second key encrypts the secondplain text characters and so on.  Afterall the keys are used, they are recycled. Thus, if we have 30 one letter keys, every 30th character inthe plain text would be replaced with the same key.

  This number is called as the period of thecipher.Themain features of polyalphabetic substitution cipher are:1.      It uses a set of related monoalphabeticsubstitution rules.2.      It uses a key that determines which rules isused for which transmission.   Conclusion:     Inthis wireless world now a days, the security for the data has become highlyimportant since the communication by transmitting of digital products over theopen network occur very frequently.

In this paper, it has been surveyed thatthe existing works on the encryption substitution techniques. Those encryptionsubstitution techniques are studied and analyzed well to promote theperformance of the encryption methods also to ensure the security proceedings.To sum up, all the techniques are useful for real-time encryption. Eachtechnique is unique in its own way, which might be suitable for differentapplications. Everyday new encryption technique is evolving hence fast andsecure conventional encryption substitution techniques will always work outwith high rate of security.

                           Reference:1. William Stallings ” NetworkSecurity Essentials (Applications and Standards)”, Pearson Education, 2004.  2.Turki Al-Somani ,Khalid Al-Zamil “Performance Evaluation of ThreeEncryption/Decryption Algorithms on the SunOS and Linux Operating Systems”,Theses3.      www.

ijarcsse.com4.      Thambiraja,Ramesh, Umarani. A survey on various most common encryption techniques in theproceeding of the ijarcsse.

5.      Cryptographyand network security by Atul Kahate(second edition)6.      https://learncryptography.com7.      https://www.techopedia.com