1. The document summarizes the Playfair cipher and Vigenere cipher. The Playfair cipher encrypts text as digraphs (pairs of letters) using a 5x5 grid, while the Vigenere cipher uses a polyalphabetic substitution cipher where the alphabet is shifted according to a repeating keyword. 2. The Playfair cipher encryption involves splitting the plaintext into pairs, and then looking at the letters' positions in the grid to determine which letters to substitute. If both letters are in the same row/column, letters are taken from that row/column. Otherwise, a rectangle is formed to find the substitution. 3. The Vigenere cipher adds the letters of the plaintext and keyword modulo 26

1. PLAYFAIR AND VIGENERE CIPHER
Name: Md Fazle Rabbi
ID:16CSE057

2. CONTENTS
 Introduction of Playfair
 Encryption Technique of Playfair
 Introduction of Vigenere Cipher
 Technique of Vigenere Cipher
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3. INTRODUCTION OF PLAYFAIR
 The Playfair cipher was the first practical digraph
substitution cipher. The scheme was invented
in 1854 by Charles Wheatstone but was named after
Lord Playfair who promoted the use of the cipher.
 It was used for tactical purposes by British forces in the
Second Boer War and in World War I and for the same
purpose by the Australians during World War II. This was
because Playfair is reasonably fast to use and requires no
special equipment.
 In this scheme, pairs of letters are encrypted, instead of
single letters as in the case of simple substitution cipher.
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4. ENCRYPTION TECHNIQUE
 Pair cannot be made with same letter. Break the
letter in single and add a bogus letter to the
previous letter.
Plain Text: “hello”
After Split: ‘he’ ‘lx’ ‘lo’
Here ‘x’ is the bogus letter.
 2. If the letter is standing alone in the process of
pairing, then add an extra bogus letter with the
alone letter
Plain Text: “helloe”
AfterSplit: ‘he’ ‘lx’ ‘lo’ ‘lz’
Here ‘z’ is the bogus letter.
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5.  If both the letters are in the same column: Take
the letter below each one (going back to the top if at
the bottom).
For example:
Diagraph: "me"
Encrypted Text: cl
Encryption:
m -> c
e -> l
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6.  If both the letters are in the same row: Take the
letter to the right of each one (going back to the
leftmost if at the rightmost position).
For example:
Diagraph: "sty“
Encrypted Text: tl
Encryption:
s -> t
t -> l
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7.  If neither of the above rules is true: Form a
rectangle with the two letters and take the letters on
the horizontal opposite corner of the rectangle.
For example:
Diagraph: "nt"
Encrypted Text: rq
Encryption:
n -> r
t -> q
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8. INTRODUCTION OF VIGENERE CIPHER
 Vigenere Cipher is a method of encrypting
alphabetic text. It uses a simple form
of polyalphabetic substitution.
 A polyalphabetic cipher is any cipher based on
substitution, using multiple substitution alphabets .
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9. TECHNIQUE OF VIGENERE CIPHER
 The alphabet used at each point depends on a
repeating keyword.
 Encryption The plaintext(P) and key(K) are added
modulo 26.
 Ci = (Pi + K) mod 26
 Decryption:
 Pi = (Ci - K) mod 26
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10. VIGENERE CIPHER ENCRYPTION
 Encryption The plaintext(P) and key(K) are added
modulo 26.
 Ci = (Pi + K) mod 26
 Decryption:
 Pi = (Ci - K) mod 26
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11. VIGENERE CIPHER ENCRYPTION
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12. VIGENERE CIPHER ENCRYPTION
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13. VIGENERE CIPHER DECRYPTION
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14. THE END