Caesar Ciphers

Ostensibly used by the Roman Empire, a Caesar cipher is a simple alphabetic rotation. The most popular implementation (used these days to obscure potentially offensive content or the answers to quizzes, on the presumption that everyone will be able to decrypt it, but may want not to see it upon first loading) is rot13, which performs this transformation:

a b c d e f g h i j k l m n o p q r s t u v w x y z
n o p q r s t u v w x y z a b c d e f g h i j k l m

(rot13's handy because performing the enciphering operation again deciphers. This is a property that's often attractive in ciphers.)

history WW II-era Ciphers bit-wise transformations
modern basics