Write a short note on the cipher 'Viginiere' (10-Marks Question)
Answers
Answer:
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Explanation:
Vigenère 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 .The encryption of the original text is done using the Vigenère square or Vigenère table.
The table consists of the alphabets written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet, corresponding to the 26 possible Caesar Ciphers.
At different points in the encryption process, the cipher uses a different alphabet from one of the rows.
The alphabet used at each point depends on a repeating keyword.
Example:
Input : Plaintext : GEEKSFORGEEKS Keyword : AYUSH Output : Ciphertext : GCYCZFMLYLEIM For generating key, the given keyword is repeated in a circular manner until it matches the length of the plain text. The keyword "AYUSH" generates the key "AYUSHAYUSHAYU" The plain text is then encrypted using the process explained below.
Encryption
The first letter of the plaintext, G is paired with A, the first letter of the key. So use row G and column A of the Vigenère square, namely G. Similarly, for the second letter of the plaintext, the second letter of the key is used, the letter at row E and column Y is C. The rest of the plaintext is enciphered in a similar fashion.