Keyed Caesar Cipher

A monoalphabetic substitution cipher that shifts a plaintext alphabet by a certain number of places to the right to produce a cipher alphabet. In a variation known as the keyed Caesar cipher, the plaintext alphabet is 'keyed' (prefixed) with non-repeating letters from a chosen passphrase or word, and the resulting keyed alphabet is then shifted. Of particular note is a Caesar cipher of shift 13 performed on the English alphabet—known as rot13—because enciphering and deciphering are symmetric operations.