Atbash Cipher Encoder & Decoder
What is the Atbash Cipher?
The Atbash cipher is a particular type of substitution cipher originally developed for the Hebrew alphabet, but can be applied to any alphabet. It works by substituting each letter with its "mirror" in the alphabet - the first letter becomes the last, the second becomes the second-to-last, and so on.
Historical Background
The name "Atbash" comes from the Hebrew alphabet. It's formed by taking the first letter (Aleph - א), the last letter (Tav - ת), the second letter (Bet - ב), and the second-to-last (Shin - ש), creating "A-T-B-Sh."
The Atbash cipher appears in the Hebrew Bible, where it was used to encrypt certain words. For example, in the Book of Jeremiah, the word "Sheshach" (ששך) is believed to be an Atbash encryption of "Babel" (בבל).
How Does It Work?
In the English alphabet, the substitution table looks like this:
| Plain | A | B | C | D | E | F | G | H | I | J | K | L | M |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cipher | Z | Y | X | W | V | U | T | S | R | Q | P | O | N |
| Plain | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cipher | M | L | K | J | I | H | G | F | E | D | C | B | A |
Self-Reciprocal Property
A unique property of the Atbash cipher is that it's self-reciprocal (also called an involution). This means that the same algorithm is used for both encoding and decoding. If you encode "HELLO" to get "SVOOL," encoding "SVOOL" will give you back "HELLO."
Example
| Original | Atbash | Result |
|---|---|---|
| HELLO | → | SVOOL |
| WORLD | → | DLIOW |
| CIPHER | → | XRKSVI |
Security Considerations
The Atbash cipher provides minimal security as it has no key - once you know the method, you can decode any message. It's easily broken through:
- Frequency analysis (common letters like E, T, A remain common, just substituted)
- Pattern recognition (short words like "the", "and" are easily identified)
- Simple trial-and-error
Despite its weakness, Atbash remains popular in puzzles, games, and as an educational introduction to cryptography.