Shifting each letter in the alphabet a fixed number of spaces to the right or left is an example of what?

Shifting each letter in the alphabet a fixed number of spaces to the right or left exemplifies single substitution encryption. In this method, each letter in the plaintext is replaced by another letter a fixed number of positions away in the alphabet, defining a straightforward one-to-one relationship between the letters. This technique is characterized by the use of a single substitution method that remains constant throughout the message, hence the term "single substitution."

This particular encryption method is simple and forms the basis for classic ciphers like the Caesar Cipher. The predictable nature of the shift means that if the shift amount is known, anyone can easily decode the message.

In contrast, multi-alphabet encryption, transposition ciphers, and polyalphabetic ciphers involve more complex forms of encryption that either use multiple substitution alphabets or rearrangement of the letters. These methods offer greater security by obscuring the relationships between the plaintext and ciphertext letters more effectively than a simple fixed shifting technique.