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Vigenère Cipher

- Substitution Cipher

The Vigenère Cipher is a classical cryptographic method that enhances the security of simple substitution ciphers. It was developed by the French diplomat Blaise de Vigenère in the 16th century.

In the Vigenère Cipher, the key to encryption is a secret word or phrase known only to the sender and recipient. Unlike the Caesar Cipher (a type of substitution cipher with a fixed shift value), the Vigenère Cipher uses a keyword of varying length. Each letter of the keyword corresponds to a specific shift value in the alphabet.

To encrypt a message using the Vigenère Cipher, the sender repeats the keyword as many times as necessary to match the length of the plaintext message. Each letter of the keyword is then aligned with a letter in the plaintext, and the corresponding shift value is applied.

By using different shift values for each letter of the keyword, the Vigenère Cipher creates a more complex encryption pattern that makes it challenging for cryptanalysts to decipher without knowing the keyword.

Decryption of the Vigenère Cipher requires the recipient to possess the correct keyword. By applying the reverse shift for each letter of the keyword, the original message is revealed.

Although the Vigenère Cipher was considered unbreakable for several centuries, it eventually succumbed to frequency analysis and other cryptographic techniques. Nonetheless, it remains a significant historical advancement in cryptography and continues to be a valuable tool for learning cryptographic principles and techniques.