Atbash Cipher Encoder & Decoder

Mirror each letter of the alphabet — A↔Z, B↔Y. Encoding and decoding are the same.

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💡 Tip: Atbash maps each letter to its mirror — A↔Z, B↔Y, M↔N. Apply Atbash twice and you get the original text back.

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What is the Atbash Cipher?

The Atbash cipher is a simple monoalphabetic substitution cipher in which each letter is replaced by its mirror in the alphabet: A↔Z, B↔Y, C↔X, and so on. Originally devised for the Hebrew alphabet, it adapts naturally to any alphabet of fixed length.

Because the substitution is its own inverse, the same operation both encodes and decodes Atbash messages — no key management required.

How the Atbash Cipher Works

Substitution table:

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

Example:

Plaintext: HELLO WORLD
Ciphertext: SVOOL DLIOW

Mathematical Formula

Atbash(x) = 25 − x
Where x is the position of the letter (A=0, Z=25). Self-inverse: Atbash(Atbash(x)) = x.

History of the Atbash Cipher

Atbash originated with Hebrew scribes around 500–600 BCE. The name itself encodes the rule: Aleph–Tav, Beth–Shin — the first letter swaps with the last, the second with the second-to-last, and so on.

The cipher appears in the Book of Jeremiah, where the word “Sheshach” is widely interpreted as Atbash for “Babel” (Babylon). It is one of the oldest documented cryptographic techniques.

Atbash Security

Atbash is not secure:

  • There is no key — the substitution is fixed and public.
  • Letter frequencies are perfectly preserved (E↔V, T↔G), making frequency analysis trivial.
  • It is best treated as a historical curiosity or puzzle aid, not as encryption.