Atbash (Hebrew: אתבש; also transliterated Atbaš) is a mono-alphabetic substitution cipher originally used to encode the Hebrew alphabet. It can be modified for use with any known alphabet.
Contents
History
The name derives from the first, last, second, and second to last Hebrew letters (Aleph-Tav-Beth-Shin).
The Atbash cipher for the modern Hebrew alphabet would be:
In the Bible
Several Biblical verses are described by commentators as being examples of Atbash:
Use
It works by substituting the first letter of an alphabet for the last letter, the second letter for the second to last and so on, effectively reversing the alphabet. An Atbash cipher for the Latin alphabet would be as follows:
An easier, simpler, and faster way of doing this is:
Examples
A few English words also 'Atbash' into other English words: "irk"="rip", "low"="old", "hob"="sly", "hold"="slow", "holy"="slob", "horn"="slim", "glow"="told", "grog"="tilt" and "zoo"="all". Some other English words 'Atbash' into their own reverses, e.g., "wizard" = "draziw."
Relationship to the affine cipher
The Atbash cipher can be seen as a special case of the affine cipher.
Under the standard affine convention, an alphabet of m letters is mapped to the numbers 0, 1, ..., m − 1. (The Hebrew alphabet has m = 22, and the standard Latin alphabet has m = 26). The Atbash cipher may then be enciphered and deciphered using the encryption function for an affine cipher, by setting a = b = (m − 1):
This may be simplified to:
If, instead, the m letters of the alphabet are mapped to 1, 2, ..., m, then the encryption and decryption function for the Atbash cipher becomes: