Final answer:
Alex should utilize the method of confusion to change a single character of plaintext into multiple characters of ciphertext. This method enciphers text to make the relationship between the ciphertext and the key complex, different from diffusion, steganography, and obfuscation.
Step-by-step explanation:
To fulfill the requirement of changing a single character of plaintext into multiple characters of ciphertext, Alex should use a method called confusion. Confusion is a cryptographic technique where the relationship between the key and the ciphertext is as complex as possible to thwart attempts at cryptanalysis. Unlike confusion, the other options such as diffusion spreads out the influence of a single plaintext symbol over many ciphertext symbols, steganography hides a secret message within another object to make it undetectable, and obfuscation makes something unclear or unintelligible rather than encrypting it.
The Zimmerman Telegram is an example that used a form of encryption known as a transposition cipher. This type of cipher rearranges the letters in the plaintext according to a set rule. By dividing the plaintext into blocks, and applying the same rule to change the order of the letters within each block, a keyword can often determine both the size of the blocks and the specific rearrangement that will occur within each block.