cipher | Definition, Types, & Facts | Britannica

Cipher, any method of transforming a message to conceal its meaning. The term is also used synonymously with ciphertext or cryptogram in reference to the ... cipher Sections&Media Article Introduction FastFacts Facts&RelatedContent Media Images AdditionalInfo MoreArticlesOnThisTopic Contributors ArticleHistory Home Geography&Travel Languages cipher cryptology Alternatetitles:ciphersystem,cryptosystem,single-keycryptography Print Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/topic/cipher More GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). 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ExternalWebsites Cryptography-SimpleSubstitutionCiphers KhanAcademy-Ciphersvs.codes BritannicaWebsites ArticlesfromBritannicaEncyclopediasforelementaryandhighschoolstudents. ciphersandcodes-StudentEncyclopedia(Ages11andup) By TheEditorsofEncyclopaediaBritannica | ViewEditHistory ADFGVXcipher Seeallmedia KeyPeople: AgnesMeyerDriscoll ...(Showmore) RelatedTopics: DataEncryptionStandard public-keycryptography transpositioncipher substitutioncipher productcipher ...(Showmore) Seeallrelatedcontent→ cipher,anymethodoftransformingamessagetoconcealitsmeaning.Thetermisalsousedsynonymouslywithciphertextorcryptograminreferencetotheencryptedformofthemessage.Abrieftreatmentofciphersfollows.Forfulltreatment,seecryptology.Allciphersinvolveeithertranspositionorsubstitution,oracombinationofthesetwomathematicaloperations—i.e.,productciphers.Intranspositionciphersystems,elementsoftheplaintext(e.g.,aletter,word,orstringofsymbols)arerearrangedwithoutanychangeintheidentityoftheelements.Insubstitutionsystems,suchelementsarereplacedbyotherobjectsorgroupsofobjectswithoutachangeintheirsequence.Insystemsinvolvingproductciphers,transpositionandsubstitutionarecascaded;forexample,inasystemofthistypecalledafractionationsystem,asubstitutionisfirstmadefromsymbolsintheplaintexttomultiplesymbolsintheciphertext,whichisthensuperencryptedbyatransposition.Alloperationsorstepsinvolvedinthetransformationofamessagearecarriedoutinaccordancetoaruledefinedbyasecretkeyknownonlytothesenderofthemessageandtheintendedreceiver. BritannicaQuiz Codes,Secrets,andCiphersQuiz Whatisthebest-knownpublic-keyschemecryptoalgorithm?Whoweretheinventorsofthefirst transpositioncipher?Testyourknowledge.Takethequiz. Cipherdevicesormachineshavecommonlybeenusedtoencipheranddeciphermessages.ThefirstcipherdeviceappearstohavebeenemployedbytheancientGreeksaround400bceforsecretcommunicationsbetweenmilitarycommanders.Thisdevice,calledthescytale,consistedofataperedbatonaroundwhichwasspirallywrappedapieceofparchmentinscribedwiththemessage.Whenunwrappedtheparchmentboreanincomprehensiblesetofletters,butwhenwrappedaroundanotherbatonofidenticalproportions,theoriginaltextreappeared.OthersimpledevicesknownascipherdiskswereusedbyEuropeangovernmentsfordiplomaticcommunicationsbythelate1400s.Thesedevicesconsistedoftworotatingconcentriccircles,bothbearingasequenceof26letters.Onediskwasusedtoselectplaintextletters,whiletheotherwasusedforthecorrespondingciphercomponent.In1891ÉtienneBazeries,aFrenchcryptologist,inventedamoresophisticatedcipherdevicebasedonprinciplesformulatedbyThomasJeffersonoftheUnitedStatesnearlyacenturyearlier.Bazeries’sso-calledcylindricalcryptographwasmadeupof20numberedrotatabledisks,eachwithadifferentalphabetengravedonitsperiphery.Thediskswerearrangedinanagreed-uponorderonacentralshaftandrotatedsothatthefirst20lettersofthemessageplaintextappearedinarow;theciphertextwasthenformedbyarbitrarilytakingoffanyotherrow.Theremaininglettersofthemessageweretreatedinthesameway,20lettersatatime.Advancesinradiocommunicationsandelectromechanicaltechnologyinthe1920sbroughtaboutarevolutionincryptodevices—thedevelopmentoftherotorciphermachine.Onecommontypeofrotorsystemimplementedproductcipherswithsimplemonoalphabeticsubstitutionciphersasfactors.Therotorsinthismachineconsistedofdiskswithelectricalcontactsoneachsidethatwerehardwiredtorealizeanarbitrarysetofone-to-oneconnections(monoalphabeticsubstitution)betweenthecontactsonoppositesidesoftherotor.TherotorciphermachinewasusedextensivelybyboththeAlliedandtheAxispowersduringWorldWarII,withthemostnotablesuchdevicebeingtheGermanEnigmamachine.Theapplicationofelectroniccomponentsinsubsequentyearsresultedinsignificantincreasesinoperationspeedthoughnomajorchangesinbasicdesign.Sincetheearly1970s,cryptologistshaveadaptedmajordevelopmentsinmicrocircuitryandcomputertechnologytocreatenew,highlysophisticatedformsofcryptodevicesandcryptosystems,asexemplifiedbytheFibonaccigeneratorandtheimplementationoftheDataEncryptionStandard(DES)throughtheuseofmicroprocessors.TheEditorsofEncyclopaediaBritannicaThisarticlewasmostrecentlyrevisedandupdatedbyErikGregersen.