Atbash Cipher Encoder & Decoder

Atbash is a substitution cipher that flips the alphabet. The first letter swaps with the last, the second with the second-to-last, and so on. Hello becomes Svool. Because each swap works both ways, running Atbash twice gives back the original text. Encoding and decoding are the same step.

It started with the Hebrew alphabet. The name spells out the first two pairs: Aleph swaps with Taw, and Bet with Shin, giving A-T-B-Sh. Commentators read several words in the Book of Jeremiah as Atbash. The best known is Sheshach in Jeremiah 25:26, which decodes to Babel, meaning Babylon.

A ↔ Z B ↔ Y C ↔ X D ↔ W E ↔ V F ↔ U G ↔ T H ↔ S I ↔ R J ↔ Q K ↔ P L ↔ O M ↔ N

A quick check: number the letters A = 1 to Z = 26, and each pair adds up to 27. H is 8, so it pairs with letter 19, which is S.

Write the alphabet on one line and the same alphabet backwards under it. For each letter of the coded message, find it on one line and read the letter on the other. Svool becomes S → H, v → e, o → l, o → l, l → o: Hello.

There is no key to find and no shift to guess. That makes Atbash easy to use, but anyone who knows the trick can read it, so it hides nothing from a curious reader. For anything private, use real encryption.

A few English words land on other real words: holy → slob, glow → told, hob → sly. And wizard becomes draziw, which is wizard spelled backwards.

Atbash and the Caesar cipher both replace one letter with another. A Caesar cipher moves every letter the same number of places (A → D with a shift of 3), so decoding needs the shift run backwards. Atbash mirrors the alphabet instead, so the same step does both jobs. ROT13, a shift of 13, also decodes itself, because 13 is half of 26.