Atbash
Template:Short description Template:One source
Atbash (Template:Langx; also transliterated Atbaš) is a monoalphabetic substitution cipher originally used to encrypt the Hebrew alphabet. It can be modified for use with any known writing system with a standard collating order.
Encryption
The Atbash cipher is a particular type of monoalphabetic cipher formed by taking the alphabet (or abjad, syllabary, etc.) and mapping it to its reverse, so that the first letter becomes the last letter, the second letter becomes the second to last letter, and so on. For example, the ISO basic Latin alphabet would work like this: Template:Aligned table
Because there is only one way to perform this, the Atbash cipher provides no communications security, as it lacks any sort of key. If multiple collating orders are available, which one was used in encryption can be used as a key, but this does not provide significantly more security, considering that only a few letters can give away which one was used.
History
The name derives from the first, last, second, and second to last Hebrew letters (Aleph–Taw–Bet–Shin).
The Atbash cipher for the modern Hebrew alphabet would be: Template:Aligned table By shifting the correlation one space to the left or the right, one may derive a variant Batgash (named for Bet–Taw–Gimel–Shin) or Ashbar (for Aleph–Shin–Bet–Reish). Either alternative mapping leaves one letter unsubstituted; respectively Aleph and Taw.
In the Bible
Several biblical words are described by commentators[n 1] as being examples of Atbash:[1][2][3]
- Jeremiah 25:26 – "The king of Sheshach shall drink after them" – Sheshach meaning Babylon in Atbash (<templatestyles src="Script/styles_hebrew.css" />בבל bbl → <templatestyles src="Script/styles_hebrew.css" />ששך ššk).
- Jeremiah 51:1 – "Behold, I will raise up against Babylon, and against the inhabitants of Lev-kamai, a destroying wind." – Lev-kamai meaning Chaldeans (<templatestyles src="Script/styles_hebrew.css" />כשדים kśdym → <templatestyles src="Script/styles_hebrew.css" />לבקמי lbqmy).
- Jeremiah 51:41 – "How has Sheshach been captured! and the praise of the whole earth taken! How has Babylon become a curse among the nations!" – Sheshach meaning Babylon (<templatestyles src="Script/styles_hebrew.css" />בבל bbl → <templatestyles src="Script/styles_hebrew.css" />ששך ššk).
Regarding a potential Atbash switch of a single letter:
- Script error: No such module "Bibleverse". - "Any place I will mention My name" (<templatestyles src="Script/styles_hebrew.css" />אזכיר) → "Any place you will mention My name" (<templatestyles src="Script/styles_hebrew.css" />תזכיר) (a → t), according to Yom Tov Asevilli[4]
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
See also
Notes
References
- Script error: No such module "citation/CS1".
External links
- ↑ Script error: No such module "citation/CS1".
- ↑ Script error: No such module "citation/CS1".
- ↑ Script error: No such module "Citation/CS1".
- ↑ Midrash Shmuel on Avot 3:6; see discussion in David Zvi Hoffmann to Exodus 20:20