Polyalphabetic Cipher

Polyalphabetic Cipher is a Substitution Cryptographic #algorithm where the same plaintext letter could be replaced by several ciphertext letters depending on its position in plaintext. The relationship between a character in the plaintext and a character in the ciphertext is one-to-many, thus make it hard to crack using Frequency Analysis# and more secure than Monoalphabetic Cipher.

However, it is not without possible attacks. If the key length is too short, then Kasiski Method# could be used to crack out the plaintext.

The following examples employed some form of Polyalphabetic Cipher:

Vigenère Cipher#

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Vigenère Cipher

Vigenère Cipher is a #Polyalphabetic Cipher which is basically multiple interwoven Shift Cipher# using a long key with the length of the list of alphabets used.
TAC3121 Chapter 3: Classic Ciphers

Polyalphabetic Cipher
Substitution Cryptography

Polyalphabetic Cipher#
Kasiski Method

Kasiski Method is a #Cryptanalytic Attack, developed by Baddage and Kasiski, attempts to break #Polyalphabetic Cipher by deducing the length of the keyword. The repetition in the ciphertext, especially in Vigenère Cipher gives clues to the key length by examining the period apart between multiple identical ciphertext patterns and find out the common factor# of the distances (excluding 1 as a possible key length). After that, we could easily do a Frequency Analysis on the ciphertext.

#cryptography #algorithm