An improvement on the Caesar cipher that uses more than one shift is called Multialphabet substitution.

An improvement on the Caesar cipher that uses more than one shift is called Multialphabet substitution.

• A. Multialphabet substitution
• B. Vigenère cipher
• C. Polyalphabetic substitution
• D. Monoalphabetic substitution

Answer: (A)

Using more than one shift changes a Caesar-style encoding into a polyalphabetic substitution. A fixed shift maps every letter to the same counterpart, making it vulnerable to frequency analysis. When shifts vary across the message, you effectively use multiple alphabets, so the same plaintext letter can map to different ciphertext letters depending on its position. That description matches the idea of using multiple shifts directly. Among the options, Multialphabet substitution is the phrasing that conveys that concept most closely. In standard terms, this is called polyalphabetic substitution, with the Vigenère cipher being a well-known implementation that uses a keyword to determine the sequence of shifts. The monoalphabetic option, by contrast, relies on a single alphabet and a fixed mapping, which doesn’t fit the “more than one shift” idea.

Using more than one shift changes a Caesar-style encoding into a polyalphabetic substitution. A fixed shift maps every letter to the same counterpart, making it vulnerable to frequency analysis. When shifts vary across the message, you effectively use multiple alphabets, so the same plaintext letter can map to different ciphertext letters depending on its position. That description matches the idea of using multiple shifts directly. Among the options, Multialphabet substitution is the phrasing that conveys that concept most closely. In standard terms, this is called polyalphabetic substitution, with the Vigenère cipher being a well-known implementation that uses a keyword to determine the sequence of shifts. The monoalphabetic option, by contrast, relies on a single alphabet and a fixed mapping, which doesn’t fit the “more than one shift” idea.