Editing Vigenère cipher (section)

{{short description|Simple type of polyalphabetic encryption system}}
[[File:Vigenere.jpg|right|thumbnail|The Vigenère cipher is named after [[Blaise de Vigenère]] (pictured), although [[Giovan Battista Bellaso]] had invented it before Vigenère described his [[autokey cipher]].]]
[[File:Confederate cipher disk.png|right|thumb|A reproduction of the [[Confederate States of America|Confederacy]]'s [[cipher disk]] used in the [[American Civil War]] on display in the [[National Cryptologic Museum]]]]

The '''Vigenère cipher''' ({{IPA|fr|viʒnɛːʁ}}) is a method of [[encryption|encrypting]] [[alphabetic]] text where each letter of the [[plaintext]] is encoded with a different [[Caesar cipher]], whose increment is determined by the corresponding letter of another text, the [[key (cryptography)|key]].

For example, if the plaintext is <code>attacking tonight</code> and the key is <code>oculorhinolaryngology</code>, then

*the first letter of the plaintext, <code>a</code>, is shifted by 14 positions in the alphabet (because the first letter of the key, <code>o</code>, is the 14th letter of the alphabet, counting from zero), yielding <code>o</code>; 

*the second letter, <code>t</code>, is shifted by 2 (because the second letter of the key, <code>c</code>, is the 2nd letter of the alphabet, counting from zero) yielding <code>v</code>;

*the third letter, <code>t</code>, is shifted by 20 (<code>u</code>), yielding <code>n</code>, with wrap-around;
and so on.  

It is important to note that traditionally spaces and punctuation are removed prior to encryption<ref>{{Cite web |title=Wolfram Challenges: Programming Puzzles for the Wolfram Language |url=https://challenges.wolframcloud.com/challenge/vigenere-cipher |access-date=2025-03-27 |website=challenges.wolframcloud.com}}</ref> and reintroduced afterwards. 

* In this example the tenth letter of the plaintext <code>t</code> is shifted by 14 positions (because the tenth letter of the key <code>o</code> is the 14th letter of the alphabet, counting from zero.) Therefore, the encryption yields the message <code>ovnlqbpvt hznzeuz</code>. 

If the recipient of the message knows the key, they can recover the plaintext by reversing this process.

The Vigenère cipher is therefore a special case of a [[polyalphabetic cipher|polyalphabetic substitution]].<ref>{{cite book |author1=Bruen, Aiden A. |author2=Forcinito, Mario A. |title=Cryptography, Information Theory, and Error-Correction: A handbook for the 21st Century|publisher=John Wiley & Sons|year=2011|isbn=978-1-118-03138-4|page=21 |url = https://books.google.com/books?id=fd2LtVgFzoMC&pg=PA21}}</ref><ref>{{cite book|author=Martin, Keith M.|title=Everyday Cryptography|publisher=Oxford University Press|year=2012|isbn=978-0-19-162588-6 |page=142 |url = https://books.google.com/books?id=1NHli2uzt_EC&pg=PT142}}</ref>

First described by [[Giovan Battista Bellaso]] in 1553, the cipher is easy to understand and implement, but it resisted all attempts to break it until 1863, three centuries later. This earned it the description ''le chiffrage indéchiffrable'' ([[French language|French]] for 'the indecipherable cipher').  Many people have tried to implement encryption schemes that are essentially Vigenère ciphers.<ref name="Smith1955">{{cite book|author=Laurence Dwight Smith|title=Cryptography: The Science of Secret Writing|url=https://books.google.com/books?id=8EERL-T-ziwC&pg=PA80|year=1955|publisher=Courier Corporation|isbn=978-0-486-20247-1|page=81}}</ref> In 1863, [[Friedrich Kasiski]] was the first to publish a general method of deciphering Vigenère ciphers.

In the 19th century, the scheme was misattributed to [[Blaise de Vigenère]] (1523–1596) and so acquired its present name.<ref>{{Citation |last= Rodriguez-Clark |first= Dan |title= Vigenère Cipher |publisher= Crypto Corner |year= 2017 |url= https://crypto.interactive-maths.com/vigenegravere-cipher.html }}</ref>