The kind of cipher where “A becomes B, B becomes C” is called a Caesar cipher , also known as a shift cipher. In this type of cipher, every letter in the plaintext is shifted forward (or backward) by a fixed number of positions in the alphabet.

What this cipher does

  • It uses a single substitution rule: each letter is replaced by another letter a fixed distance away in the alphabet (for example, shift by 1 makes A→B, B→C, …, Z→A).
  • Because the same rule applies to every letter, it is a very simple, classical encryption method and is easy to break with modern techniques.

Related quick fact

  • Modern descriptions often group the Caesar cipher under “classical substitution ciphers,” where each plaintext letter always maps to the same ciphertext letter.