Which cipher uses multiple substitution alphabets?

• A. Transposition Cipher
• B. Caesar Cipher
• C. Substitution Cipher
• D. Polyalphabetic Cipher

Answer: (D)

Polyalphabetic ciphers use more than one substitution alphabet, rotating through different alphabets as you encrypt each letter. This means the same plaintext letter can map to different ciphertext letters depending on its position, which makes frequency analysis much harder.

A classic example is the Vigenère cipher, which uses a keyword to determine which of several shifted alphabets to apply at each step. In contrast, a simple substitution like a fixed shift (Caesar) or any single-alphabet substitution maps every instance of a given plaintext letter to the same ciphertext letter. A transposition cipher, on the other hand, merely rearranges letters rather than substituting them.

So, the cipher that uses multiple substitution alphabets is the polyalphabetic cipher.