Apply the Atbash substitution, which mirrors the alphabet so A becomes Z and B becomes Y. It has no key, so it offers no security at all and is studied for its history.
Show calculation steps
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A mirrored alphabet
Atbash maps A to Z, B to Y and so on — the alphabet reversed. It has no key at all, which means it has exactly one possible decryption and offers no security whatsoever. It is a historical curiosity and a puzzle device.
Worked example
HELLO → SVOOL SVOOL → HELLO (applying it twice returns the original)
Its own inverse
Because the mapping is a mirror, encoding and decoding are the same operation. That property makes it convenient for puzzles and is shared with ROT13, which mirrors by rotation instead.
Where it came from
Atbash originates in Hebrew scribal practice, where the first letter maps to the last. Instances appear in the Hebrew Bible, which makes it one of the oldest substitution ciphers with a documented history.
Do not use it for anything
A monoalphabetic substitution with no key is broken by inspection: letter frequencies survive it completely, so E maps to V and stays the most common letter. If you need to protect something, use a vetted modern algorithm through a library. Transformation happens in your browser.
How to use the Atbash Cipher
- Paste your text.
- Click "Apply Atbash" – the same operation reverses it.
Frequently asked questions
Where does Atbash come from?
From Hebrew scribal tradition, where the first letter of the alphabet is exchanged with the last, the second with the second-last, and so on. The name itself encodes the rule using the first, last, second and second-last Hebrew letters. Instances appear in the Book of Jeremiah.
Why is Atbash weaker even than Caesar?
Because it has no key at all. Caesar at least has 25 possible shifts; Atbash has exactly one fixed mapping, so recognising the cipher is the same as breaking it.
Is it self-inverse?
Yes. The mapping is a mirror, so applying it twice returns the original text.
Break or check a simple cipher
Plaintext from a classical cipher, or confirmation of which one was used.
- ROT13 Encoder and DecoderTry ROT13 first: it is its own inverse, so one pass tells you immediately.
- Caesar Cipher Encoder and DecoderTry every Caesar shift, since ROT13 is only the shift-13 case.
- Atbash Cipher you are hereTry Atbash, which reverses the alphabet rather than rotating it.
- Vigenere Cipher Encoder and DecoderIf a single shift never works, the key is probably a word rather than a number.
