Which of the following is an example of a multialphabet cipher?

• A. Vigenère
• B. Caesar
• C. Playfair
• D. Atbash

Answer: (A)

Multialphabet (polyalphabetic) ciphers change the substitution alphabet as you progress through the text. The Vigenère cipher achieves this by using a keyword to determine a different shift for each plaintext letter, effectively cycling through a set of alphabets. Because the same plaintext letter can map to different ciphertext letters depending on its position, frequency patterns are harder to spot.

Caesar uses a single fixed shift for every letter, so it relies on one alphabet. Playfair encrypts digraphs using a fixed 5x5 square rather than switching alphabets, and Atbash simply maps each letter to its opposite in the alphabet, also with one fixed substitution. Hence, the Vigenère example is the one that demonstrates a multialphabet approach.