Editing Voynich manuscript (section)

=== Ciphers ===
According to the "letter-based cipher" theory, the Voynich manuscript contains a meaningful text in some European language that was intentionally rendered obscure by mapping it to the Voynich manuscript "alphabet" through a [[cipher]] of some sort—an [[algorithm]] that operated on individual letters. This was the working hypothesis for most 20th-century deciphering attempts, including an informal team of [[NSA]] cryptographers led by [[William F. Friedman]] in the early 1950s.<!--more names? SSG?--><ref name=Reeds1994 />

[[File:Vigenère square shading.svg|thumb|The Vigenère square or table may have been used for encryption and decryption.]]
The counterargument is that almost all cipher systems consistent with that era fail to match what is seen in the Voynich manuscript. For example, simple [[substitution cipher]]s would be excluded because the distribution of letter frequencies does not resemble that of any known language, while the small number of different letter shapes used implies that [[nomenclator cipher|nomenclator]] and [[homophonic cipher]]s should be ruled out, because these typically employ larger cipher alphabets. [[Polyalphabetic cipher]]s were invented by [[Leone Battista Alberti|Alberti]] in the 1460s and included the later [[Vigenère cipher]], but they usually yield ciphertexts where all cipher shapes occur with roughly equal probability, quite unlike the language-like letter distribution which the Voynich manuscript appears to have.

However, the presence of many tightly grouped shapes in the Voynich manuscript (such as "or", "ar", "ol", "al", "an", "ain", "aiin", "air", "aiir", "am", "ee", "eee", among others) does suggest that its cipher system may make use of a "verbose cipher", where single letters in a plaintext get enciphered into groups of fake letters. For example, the first two lines of page ''f15v'' contain "{{not a typo|oror or}}" and "{{not a typo|or or oro r}}", which strongly resemble how [[Roman numerals]] such as "CCC" or "XXXX" would look if verbosely enciphered.<ref name=Pelling2009>{{cite web |last=Pelling |first=Nick |date=27 August 2009 |title=Voynich cipher structure |url=http://ciphermysteries.com/2009/08/27/voynich-cipher-structure |access-date=29 June 2016|archive-date=6 July 2016|archive-url=https://web.archive.org/web/20160706174531/http://ciphermysteries.com/2009/08/27/voynich-cipher-structure |url-status=live}}</ref>