CISSP Practice Exam 2025 – Complete Prep Guide

The correct choice, which refers to a monoalphabetic cipher, relies on a single alphabet for encryption by substituting one character for another consistently throughout the text. This means each letter from the plaintext is replaced by a corresponding letter in the ciphertext, and this substitution does not change as the text progresses. For example, if a 'D' is always replaced with an 'H', it remains the same throughout the encryption process.

This method is straightforward yet can be vulnerable to frequency analysis, where attackers analyze the frequency of letters to decipher the encrypted message. Because the encryption process uses a single fixed substitution, patterns become evident if enough text is analyzed.

In contrast, transposition ciphers rearrange the letters of the plaintext according to a certain system without altering the letters themselves, making them operate quite differently from monoalphabetic ciphers. Polyalphabetic ciphers utilize multiple substitution alphabets at different points in the message for greater security, while symmetric ciphers refer generally to cryptographic systems that use the same key for both encryption and decryption, encompassing various types of ciphers including both monoalphabetic and polyalphabetic methods. Thus, the key characteristic of a monoalphabetic cipher is its reliance on a single alphabet for direct letter substitution