Final answer:
Brielle's research has led her to the ROT13 cipher, a type of substitution cipher where the alphabet is rotated by 13 positions to encrypt or decrypt a message.
Step-by-step explanation:
The cipher that Brielle is researching, where the entire alphabet is rotated 13 steps, is known as the ROT13 cipher. This is a specific type of substitution cipher where each letter in the plaintext is replaced by a letter 13 positions down the alphabet. For example, 'A' becomes 'N', 'B' becomes 'O', and so on. It is a simple and common method for obfuscating text because applying the same process again reverses the encryption. In the context of the Zimmerman Telegram, a different cipher was used, namely a Transposition Cipher. Unlike substitution ciphers like ROT13, in a transposition cipher, the letters are rearranged rather than replaced. A keyword can influence the rearrangement, resulting in a scrambled message hard to decipher without the right key.