Atbash ( he, אתבש; also transliterated Atbaš) is a monoalphabetic

substitution cipher In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the "units" may be single letters (the most common), pairs of letters, trip ...

originally used to

encrypt In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...

the

Hebrew alphabet The Hebrew alphabet ( he, wikt:אלפבית, אָלֶף־בֵּית עִבְרִי, ), known variously by scholars as the Ktav Ashuri, Jewish script, square script and block script, is an abjad script used in the writing of the Hebrew languag ...

. It can be modified for use with any known

writing system A writing system is a method of visually representing verbal communication, based on a script and a set of rules regulating its use. While both writing and speech are useful in conveying messages, writing differs in also being a reliable form ...

with a standard collating order.

Encryption

The Atbash cipher is a particular type of monoalphabetic cipher formed by taking the

alphabet An alphabet is a standardized set of basic written graphemes (called letters) that represent the phonemes of certain spoken languages. Not all writing systems represent language in this way; in a syllabary, each character represents a syll ...

(or

abjad An abjad (, ar, أبجد; also abgad) is a writing system in which only consonants are represented, leaving vowel sounds to be inferred by the reader. This contrasts with other alphabets, which provide graphemes for both consonants and vowels ...

syllabary In the linguistic study of written languages, a syllabary is a set of written symbols that represent the syllables or (more frequently) moras which make up words. A symbol in a syllabary, called a syllabogram, typically represents an (optiona ...

, 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

Latin alphabet The Latin alphabet or Roman alphabet is the collection of letters originally used by the ancient Romans to write the Latin language. Largely unaltered with the exception of extensions (such as diacritics), it used to write English and the o ...

would work like this: Due to the fact that there is only one way to perform this, the Atbash cipher provides no communications security, as it lacks any sort of

key Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that controls the operation of a cryptography algorithm * Key (lock), device used to control access to places or facilities restricted by a lock * Key (map ...

. 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 Aleph (or alef or alif, transliterated ʾ) is the first letter of the Semitic abjads, including Phoenician , Hebrew , Aramaic , Syriac , Arabic ʾ and North Arabian 𐪑. It also appears as South Arabian 𐩱 and Ge'ez . These letter ...

– Taw–

Bet Black Entertainment Television (acronym BET) is an American basic cable channel targeting African-American audiences. It is owned by the CBS Entertainment Group unit of Paramount Global via BET Networks and has offices in New York City, Los A ...

–

Shin Shin may refer to: Biology * The front part of the human leg below the knee * Shinbone, the tibia, the larger of the two bones in the leg below the knee in vertebrates Names * Shin (given name) (Katakana: シン, Hiragana: しん), a Japanese ...

). The Atbash cipher for the modern Hebrew alphabet would be:

In the Bible

Several

biblical The Bible (from Koine Greek , , 'the books') is a collection of religious texts or scriptures that are held to be sacred in Christianity, Judaism, Samaritanism, and many other religions. The Bible is an anthologya compilation of texts of a ...

words are described by commentators

Rashi Shlomo Yitzchaki ( he, רבי שלמה יצחקי; la, Salomon Isaacides; french: Salomon de Troyes, 22 February 1040 – 13 July 1105), today generally known by the acronym Rashi (see below), was a medieval French rabbi and author of a compre ...

and

Radak ''Cervera Bible'', David Qimhi's Grammar Treatise David Kimhi ( he, ר׳ דָּוִד קִמְחִי, also Kimchi or Qimḥi) (1160–1235), also known by the Hebrew acronym as the RaDaK () (Rabbi David Kimhi), was a medieval rabbi, biblical commen ...

on each of the first three verses. Also other commentators. as being examples of Atbash: * Jeremiah 25:26 – "The king of ''

Sheshach Sheshach ( he, ששך), whose king is mentioned in the Hebrew Bible in Jeremiah 25:26, is supposed to be equivalent to Babel (Babylon), according to a secret mode of writing practiced among the Jews of unknown antiquity, which consisted in substitu ...

'' shall drink after them" – Sheshach meaning

Babylon ''Bābili(m)'' * sux, 𒆍𒀭𒊏𒆠 * arc, 𐡁𐡁𐡋 ''Bāḇel'' * syc, ܒܒܠ ''Bāḇel'' * grc-gre, Βαβυλών ''Babylṓn'' * he, בָּבֶל ''Bāvel'' * peo, 𐎲𐎠𐎲𐎡𐎽𐎢 ''Bābiru'' * elx, 𒀸𒁀𒉿𒇷 ''Babi ...

in Atbash ( ''bbl'' → ''ššk''). * Jeremiah 51:1 – "Behold, I will raise up against Babylon, and against the inhabitants of ''Lev-kamai'', a destroying wind." – Lev-kamai meaning

Chaldea Chaldea () was a small country that existed between the late 10th or early 9th and mid-6th centuries BCE, after which the country and its people were absorbed and assimilated into the indigenous population of Babylonia. Semitic-speaking, it was ...

ns ( ''kšdym'' → ''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 ( ''bbl'' → ''ššk''). Regarding a potential Atbash switch of a single letter: * - "Any place ''I'' will mention My name" () → "Any place ''you'' will mention My name" () (a → t), according to

Yom Tov Asevilli Yom Tov ben Abraham of Seville ( 1260 – 1320; also Asevilli, Assevilli, Ashbili) commonly known by the Hebrew acronym Ritva, ( he, ריטב"א) was a medieval rabbi and rosh yeshiva of the Yeshiva of Seville, known for his commentaries on the T ...

Midrash Shmuel on Avot 3:6
see discussion in

David Zvi Hoffmann David Zvi Hoffmann (November 24, 1843, Verbó, Austrian Empire – November 20, 1921, Berlin) (Hebrew: דוד צבי הופמן), was an Orthodox Rabbi and Torah Scholar. He headed the Yeshiva in Berlin, and published research on the Pent ...

br>to Exodus 20:20

Relationship to the affine cipher

The Atbash cipher can be seen as a special case of the

affine cipher The affine cipher is a type of monoalphabetic substitution cipher, where each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. The formula used means that eac ...

. Under the standard affine convention, an alphabet of ''m'' letters is mapped to the numbers (The Hebrew alphabet has and the standard Latin alphabet has The Atbash cipher may then be enciphered and deciphered using the encryption function for an affine cipher by setting :

\mathrm(x) = \mathrm(x) = \big((m - 1) x + (m - 1)\big) \bmod m.

This may be simplified to :

\begin
 \mathrm(x) &= (m - 1)(x + 1) \bmod m \\
               &= -(x + 1) \bmod m.
\end

If, instead, the ''m'' letters of the alphabet are mapped to then the encryption and decryption function for the Atbash cipher becomes :

\mathrm(x) = (-x \bmod m) + 1.

Notes

References

External links

Online Atbash decoder
{{Cryptography navbox , classical Classical ciphers Jewish mysticism Hebrew-language names