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Polyalphabetic Cipher

- Substitution Cipher

The Polyalphabetic Cipher is a type of substitution cipher that enhances the security of traditional ciphers by introducing multiple alphabets or cipher alphabets. In this encryption technique, each letter of the plaintext is substituted with a corresponding letter from one of several different cipher alphabets, based on a secret key or keyword.

To encrypt a message using the Polyalphabetic Cipher, the sender selects a keyword or keyphrase that determines the arrangement of the cipher alphabets. Each letter of the keyword is used to create a distinct cipher alphabet, and these alphabets are then applied cyclically to the plaintext.

During encryption, the same letter in the plaintext may be encrypted differently depending on its position within the keyword and the corresponding cipher alphabet. This variability introduces a higher level of complexity and makes it more challenging for cryptanalysts to decipher the message through frequency analysis.

The Polyalphabetic Cipher gained significant historical prominence with the invention of the Vigenère Cipher, a well-known example of a polyalphabetic cipher. The Vigenère Cipher uses a tabula recta (a table of alphabets) to encode and decode messages, making it an effective and popular encryption method during its time.

While the Polyalphabetic Cipher offers stronger security compared to monoalphabetic ciphers, it is not as robust as modern cryptographic methods. Nonetheless, it remains an essential step in the historical evolution of encryption techniques, paving the way for more advanced and secure encryption systems used today.