CS8792 - CRYPTOGRAPHY AND NETWORK SECURITY - UNIT 1 - TOPIC 9.3 -PLAYFAIR CIPHER IN TAMIL BY ABISHA

The Playfair cipher is a classical symmetric encryption technique that was invented by Sir Charles Wheatstone in 1854, but it was named after Lord Playfair, who promoted its use. It's a type of substitution cipher that encrypts pairs of letters (digraphs), making it more secure than simple substitution ciphers. Here's how the Playfair cipher works: Key Table Setup: 1. Key Square (5x5 Grid): A key square is created by placing a keyword (without repeating letters) in a 5x5 grid. The remaining letters of the alphabet (excluding the ones in the keyword) are added to the grid in order. Example Key Square (using the keyword "KEYWORD"): ``` K E Y W O R D A B C F G H I L M N P Q S T U V X Z ``` Encryption Process: 1. Breaking the Message into Digraphs: - Break the plaintext message into pairs of letters (digraphs). - Add a filler (like 'X') if there is an odd number of letters. 2. Rule for Same Letter: - If both letters of a digraph are the same, add a filler letter ('X') after the first letter. 3. Letter Pairs in Same Row: - If both letters are in the same row of the key square, replace each letter with the letter to its right (wrapping around to the left if at the end of the row). 4. Letter Pairs in Same Column: - If both letters are in the same column of the key square, replace each letter with the letter below it (wrapping around to the top if at the bottom of the column). 5. Letter Pairs in Different Rows and Columns: - Form a rectangle with the two letters and replace each letter with the letter at the other end of the rectangle. 6. Handling Repeated Letters: - If a letter is repeated in the same digraph, insert a filler letter ('X') between them and proceed. Decryption: 1. The decryption process is the reverse of encryption. It involves finding the positions of the letters in the key square and moving accordingly. Example: Let's encrypt the message "HELLO" using the key square provided above. 1. Break the message into digraphs: "HE", "LL", "O". 2. Apply the Playfair rules to encrypt each digraph. - "HE" becomes "BY" (H and E are in the same row). - "LL" becomes "AO" (Ls are in the same column). - "O" becomes "ON" (O and N form a rectangle). So, the encrypted message is "BYAOON." Keep in mind that the Playfair cipher has limitations and is vulnerable to frequency analysis, but it provides a higher level of security compared to simpler substitution ciphers. CS8792 - CRYPTOGRAPHY AND NETWORK SECURITY - UNIT 1 - TOPIC 9.3 -PLAYFAIR CIPHER IN TAMIL BY ABISHA LIKE SHARE SUBSCRIBE ANY DOUBTS, COMMENT. HAVE A HAPPY LEARNING