Network Defense Essentials (NDE) Practice Exam 2025 - Free Network Defense Practice Questions and Study Guide

The correct answer is the transposition cipher. This type of cipher works by rearranging the letters of the plaintext to create the ciphertext, rather than substituting one letter for another. In a transposition cipher, the positions of the letters are changed according to a specific system or key, but the actual letters remain unchanged. This method relies on the order of the characters and their positions to disguise the original message.

For instance, if you have a word like "HELLO" and apply a transposition that moves the letters around, you might end up with "LEHOL" or another combination, maintaining the same letters but altering their sequence. This characteristic distinguishes transposition ciphers from others that fundamentally change the letters involved.

In contrast, a substitution cipher replaces each letter in the plaintext with a different letter, which does not focus on rearranging but rather on exchanging characters. Symmetric ciphers encompass a broader category that can include both substitution and transposition techniques, but they do not specifically focus on rearranging letters. Homophonic ciphers involve substituting letters with varying symbols to obscure frequency analysis but do not deal with rearranging the original text, often focusing on one-to-many substitutions for specific letters.