Atbash Cipher

About this calculator

This tool applies the Atbash cipher, one of the oldest known substitution ciphers, originally used for the Hebrew alphabet and later adapted to Latin script. It works by mirroring each letter's position in the alphabet: A becomes Z, B becomes Y, C becomes X, and so on, following the rule that a letter at position n maps to position (27 − n).

Because the mapping is symmetric, Atbash is its own inverse — running the cipher twice returns the original text, so the same tool both encodes and decodes. It's taught in cryptography courses as an introduction to substitution ciphers and appears in puzzles, escape rooms, and historical texts (including some Biblical cryptograms), though it offers no real security since there's only one possible key.