Atbash — Bench tool
Published 2 Sep 2026 ·
Atbash folds the alphabet in half and glues A to Z, B to Y, C to X. There is no key at all — knowledge of the method is the whole secret. It is the cleanest possible illustration of what a substitution alphabet is, and it is its own inverse, which is a property later ciphers spend real effort trying to achieve.
- Era
- Antiquity
- Type
- Substitution
- Key space
- 1 key
- Level
- Starter
IWhat this tool does
Write the 26 letters in a row. Write them a second time in reverse underneath. Read vertically.
A B C D E F G H I J K L M
Z Y X W V U T S R Q P O N
The word LOOM becomes OLLN. The word BRASS becomes YIZHH. Nothing is shifted; everything is folded.
The fold has a visible side effect: letters in the middle of the alphabet swap with near neighbours. M and N trade places, L and O trade places. The further a letter sits from the centre, the further it travels — A walks the full 25 places to Z while M only walks one.
| Plain | Cipher | Distance travelled |
|---|---|---|
| A | Z | 25 |
| G | T | 13 |
| M | N | 1 |
| N | M | 1 |
| Z | A | 25 |
IIThe key
Zero. There is one mapping and everyone who knows the method has it.
This is worth pausing on, because the term 'key' has just been shown to be optional. A cipher can be perfectly well defined, fully reversible, and completely public. Its only protection is that most people have never heard of it.
A cipher whose secret is 'nobody has read the manual' has a key space measured in ignorance.
Modern equivalents of the same mistake: hiding an admin panel at an unlisted URL, or trusting an unpublished API endpoint. The atbash keyspace and the atbash threat model both survive into the present day.
IIIWhat it will not protect
Historical ciphers are for study and recreation and are not suitable for protecting real information. The full analysis is in the cipher entry.
Read the full entry, with deciphering steps and weakness analysis →