Enhance Security of Playfair Matrix Using Two 12X8 Playfair Matrix

Transcription

1 Enhance Security of Playfair Matrix Using Two 12X8 Playfair Matrix Pavan Kumar*, Vedant Rastogi** Department of Computer Science & Engineering IET, Alwar - ABSTRACT In the last some decades in digital world, communication of information is very hazardous in the charisma of the third party on internet. There cryptography is used to safe and sound information in order to offer the solitude for the planned sender as well as receiver by managing the message with the Symmetric and Asymmetric key cryptography. The purpose of this work is to securing the message (cipher text) of playfair technique of size12x8 using second matrix of same size of 12X8. It s in two-part algorithm. In I st stage existing playfair cipher customized by mounting in size of matrix, so that restrictions of former works of playfair (PF) cipher using 5 5 matrix were conquer in proposed work. In this proposed scheme, use a 12 8 matrix that contains many alphabetic, numeric and special character use as input. This work is an step up to existing algorithms that uses 5 5 matrix to pick cipher characters. It makes use of alphabets both type lower case as well as upper case characters, number as well as special characters on behalf of constructing the contents of the matrix and after this we use the rotation factor to turn around the matrix. In II nd stage, we check the position of plain text in second matrix and make cipher text by it. This cipher text is sent to receiver end, at receiver end receiver check the position of this cipher text in second matrix and saves theses position and gets the plain text by seeing these positions in this first matrix. By these matrixes we can decrypt this cipher text and get plain text finally, security strength of whole system has been analyzed and tried to fulfill necessity of security. At the last, dissertation presents the scope for further work and concludes the dissertation. Keywords: Playfair=PF, Plaintext=PT, Plaintext1=PT1, Plaintext2=PT2, Cipher text= CT, Cipher text1= CT1, Cipher text2= CT2, Encryption Technique=ET, Decryption Technique=DT 1. INTRODUCTION 1.1 Introduction about PlayfairTechnique The basic Playfair cipher uses a matrix of 5 5 containing a key or phrase. Memorization of the key is achieved by generating a 5 5 key table and cipher text is created by applying four simple rules on this key table [1]. To generate the key table, one would first fill in the spaces in the table with the letters of the key (dropping any duplicate letters), then fill the remaining spaces with the rest of the letters of the alphabet in order (usually omitting "Q" to reduce the alphabet to fit; other versions put both "I" and "J" in the same space) [1]. The key can be written in the top rows of the table, from left to right, or in some other pattern, such as a spiral beginning in the upper-lefthand corner and ending in the center. The key together with the conventions for filling in the 5 5 table constitute the cipher key [1]. To encrypt a message, one would break the message into digraphs (groups of 2 letters) for example; "HELLO WORLD" becomes "HE, LL, OW, OR, LD", and maps them out on the key table. If needed, append a "Z" to complete the final digraph. The two letters of the digraph are considered as the opposite corners of a rectangle in the key table [2]. Note the relative position of the corners of this rectangle. Then apply the following 4 rules, in Page 1 of 10

2 order, to get encrypted message for each pair of letters in the PT [1] Rules for making CT using PF Matrix 1. Add an "X" after the first letter, if both letters are the same (or only one letter is left). Encrypt the new pair and continue doing this. Some variants of PF use "Q" instead of "X", but any uncommon monograph will do. 2. If both alphabets appear on the same row in table, replace them with the letters to their immediate right respectively (wrapping around to the left side of the row if a letter in the original pair was on the right side of the row). 3. If both alphabets appear on the same column in table, replace them with the letters immediately below respectively (wrapping around to the top side of the column if a letter in the original pair was on the bottom side of the column). 4. If both alphabets are not on the same row or column, replace them with the letters on the same row respectively but at the other pair of corners of the rectangle defined by the original pair. The order is important the first letter of the encrypted pair is the one that lies on the same row as the first letter of the PT pair. The decryption process, use the INVERSE (opposite) of the last 3 (2,3,4) rules, and the 1st as-is (dropping any extra "X"s (or "Q"s) that do not make sense in the final message when finished) [2] Limitations of 5 5 Matrix 1. The 5 5 Matrix considers the letters I and J as one character. 2. Only 26 letters alone can take as key without duplicates. 3. The Space between two words in the PT is not considered as one character. 4. The special characters cannot use as and numbers. 5. The uppercase alphabets are only used in 5x5 Matrix. 6. An extra letter X is added when the PT word consists of odd number of characters. In the DP this X is ignored. X is a valid character and creates confusion because it could be a part of PT, so we cannot simply remove X in DP. 7. X is used a filler letter while repeating letter falls in the same pair are separated. 2. PROPOSED WORK The proposed work consists of the following two steps: construct a modified table of Playfair cipher technique of size 12X8, which contain all the alphabets from A to Z upper case and a to z in lower case, all the special characters which are on the keyboard and all numeric values (from 0 to 9). Construct second matrix of same size 12X8 with ASCII code 8 values from 128 to 223. The PF encryption technique is dividing into two phases: a) First phase is creation and population of first Matrix (by using the key and rotate the matrix with rotation factor after insert the key without duplicate). Check the position of the character in pair of two characters in the first matrix. b) The second phase is encryption process of the plain text message with the help of the Matrix. Make the Cipher text (CT1) of the plain text. Playfair Cipher Phase -1:Creation matrix with the help of Playfair key and population of matrix after inserting key and rotate the matrix with rotation factor. Phase-2:Encryption Process Fig. 2.1 Playfair cipher encryption steps [4] Page 2 of 10

3 At the Receiver ends. Step 2: Construct second matrix of same size 12X8 with ASCII code 8 values from 128 to 223. Take the CT in pair of two characters and check its positions in the second matrix. Step 4: construct a modified table of Playfair cipher technique of size 12X8, which contain all the alphabets form A to Z upper case and a to z in lower case, all the special characters which are on the keyboard and all numeric values (from 0 to 9). The PF decryption technique is divided into two phases: c) First phase is creation and population of Matrix (by using the key). d) The second phase is decryption process of the cipher text (CT1) by the position in the second matrix with the help of the first matrix and makes the plain text. Playfair Cipher Phase -1:Creation matrix with the help of Playfair key and population of matrix after inserting key and rotate the matrix with rotation factor. Phase-2:Decryption Process Fig. 2.2 Playfair cipher decryption steps[4] 1. In the second step, use the key as a PT in RSA algorithm to make the PT of the key and send to the receiver. At the receiver end decrypt the PT into PT (key). By this key make the PF Matrix and decrypt the message. 3. ALGORITHM At the sender ends. Step 1: In the first phase: 1. If in plaintext if there is odd number of character then add the Null character in the last of the key. i. Use two PF matrix size of ii. In First matrix we insert the key without duplicate and fill up the key in the PF matrix without any duplicate from left side to right side and from top to bottom of the PF matrix side, then fill the remaining cells with the upper given tables. iii. In second matrix we use the ASCII code from 128 to If both alphabets appear on the same row in PF matrix table, replace them with the letters which is their immediate in right side respectively (if a letter in the original PT pair was on the right side of the row of PF matrix than wrapping around to the left side of the row) [29]. 3. If both alphabets appear on the same column in PF matrix table, replace them with the letters which is their immediately below side respectively (if a letter in the original PT pair was on the bottom side of the column of PF matrix then wrapping around to the top side of column of the PF matrix) [29]. 4. If both alphabets of PT are not on the same row or column of the PF matrix, replace them with the letters on the same row respectively but at the other pair of the corners of the rectangle in PF matrix defined by the original pair. The order is important the encrypted first letter of the pair of PT is the one that lies on the same row of the PF matrix as the first letter of the PT pair [5]. By this make the cipher text (CT) of the plain text. Send this CT at the receiver end. At the receiver ends. 1. Apply deception process on CT using matrix 2 to get the position of the character and save these position. 2. Construct the Matrix 1 at the receiver end; first insert the key without duplicate and after this insert the remaining characters in upper given tables. 3. According the position of the CT characters (in pair of 2 characters until end of cipher text) decrypt it using matrix 1 and get the original plain text. 4. Decrypt the CT to get the original PT by the extended PF Matrix. Page 3 of 10

4 4) FLOW CHART Start End Input key for the playfair matrix, input plain text PT1 If key length of playfair is Make the playfair matrix of size 12X8 of ASCII 7 code and rotate it with rotation Input plain text, take first two char as a pair and so on untill end of plain. Check position of these characters in first Add null in last of Fig. 4.1 Flow Chart of Algorithm 5. Experiment Analysis The proposed work is dividing in two phases: The first phase for Matrix construction uses all the rules of traditional Play fair matrix with these changes: The two I and J letters in upper case and lower case are considered as two different letters (I and J are different and i and j are different). It allows more than 26 (up to 96 characters without any duplicate) characters as key. It is case sensitive; it uses the upper case as well as lower case characters. Combinations of numbers efficiently can easily encrypted and decrypted efficiently by user. Combination of operators, brackets, special characters, can easily encrypted and decrypted efficiently by user. This algorithm adds the Null character to complete the pair, because the Null character can t affect the PT at the end of the word or sentence. Space between two words in PT considered as one character. In second matrix, we use the ASCII code from value 128 to 223 Save these positions Take second matrix check these positions in second matrix and make cipher text (CT) and send to. At receiver end check CT from matrix 2 save their positions make first matrix with the key and rotate the matrix with rotation factor, then decrypt CT. Page 4 of 10

5 TABLE 5.1 LIST OF UPPER CASE LETTERS, LOWER CASE LETTER, NUMERIC VALUES, OPERATORS, BRACKETS AND SPECIAL. CHARACTERS Table 5.3 Char form of the table Table 5.2 ASCII code use in second table. The key length is very large in comparison with the previous algorithms, here, so it is very difficult to find the plain text from CT without knowing a key. This algorithm can t separate a repeating PT letters with a filter letter. Page 5 of 10

6 EXAMPLE AND SNAPSHOT 6.1 Example Table 6.2 of plain text i am ram Table 6.1 second matrix for all example Inputs in examples Key=playfairexample and plain text is= i am ram for all examples After remove duplicate =playfirexm Example 1 with rotation 0 TABLE 4.5 First 12 8 playfair matrix at sender end and receiver end for example 1, rotation 0 Fig 6.1. output of example 1 with rotation Example 1 with rotation 1 TABLE 6.3 First 12 8 playfair matrix at sender end and receiver end for example 1, rotation 1 Plain text= i am ram Page 6 of 10

7 TABLE 6.5 First 12 8 playfair matrix at end and the receiver end for example 1, rotation 3 Fig. 6.2 output of example 1 with rotation Example 1 with rotation 2 TABLE 6.4 First 12 8 playfair matrix at sender end and receiver end for example 1, rotation 2 Fig. 6.5 output of example 1 with rotation 3 Fig. 6.3 output of example 1 with rotation Example 1 with rotation Example 1 with rotation 4 Page 7 of 10

8 TABLE 4.7 First 12 8 playfair matrix at sender and receiver end for example 1, rotation 4 TABLE 4.11 First 12 8 playfair matrix at sender and receiver end for example 1, rotation 5 Fig. 6.7 output of example 1 with rotation Example 1 with rotation 6 TABLE 6.12 First 12 8 playfair matrix at sender and receiver end for example 1, rotation 6 Fig. 6.6 output of example 1 with rotation Example 1 with rotation 5 Page 8 of 10

9 Fig.6.9 output of example 1 with rotation Example 1 with rotation 7 TABLE 6.10 First 12 8 playfair matrix at sender and receiver end for example 1, rotation 7 Fig output of example 1 with rotation 7 6. CONCLUSION So far the encryption technique adopting concept of PLAY-FAIR CIPHER MATRIX of size 5X5 has been programmed for calculating the Cipher Text. Finally, we have pointed the merits and demerits of traditional PF algorithm. In order to overcome demerits, we have proposed an extension to traditional PF cipher algorithm; which can be used more efficiently even for the Plain Text containing alphanumeric values and special characters and use the rotation factor for the high avalanche effect. Complete mathematical derivation is given to show the exact result at both sender and receiver sides the previous encryption technique is also a part of this system. After completion of program the strength of the technique has been checked and this encryption technique can also be used for other networks. In this algorithm playfair matrix is used for creating the cipher text. Page 9 of 10

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