khoor

KHOOR is the ciphertext produced when the plaintext word HELLO is encrypted using a Caesar cipher with a right shift of three. In this scheme each letter is replaced by the letter three positions later in the alphabet, wrapping around after Z. Because H becomes K, E becomes H, L becomes O, and O becomes R, HELLO maps to KHOOR. Therefore KHOOR is not an English word but a simple encoded form of HELLO.

The Caesar cipher is one of the oldest known substitution ciphers. It operates on the 26-letter Latin alphabet by applying a fixed shift to every letter. A shift of three is the canonical example often used to illustrate the method, and shifts of other values generalize to the family of ciphers known as ROT-n.

Decryption is the inverse operation: apply a left shift of three (or a right shift of 23) to recover HELLO from KHOOR. In algebraic terms, if letters are mapped to numbers A=0 through Z=25, encryption is E(x) = (x + 3) mod 26 and decryption is D(y) = (y - 3) mod 26.

KHOOR commonly appears in puzzles and educational demonstrations of basic cryptography. It illustrates how a simple, easily reversible transformation can obfuscate a message, and it serves as a stepping stone to understanding more complex cipher techniques.