알파벳으로 구성된 평문을 2개의 값으로 shift하는 key table로 암호화한 암호문이 주어졌을때 평문을 찾는 문제입니다.
소문제 1번은 경우 암호문길이가 길어서 풀 수 있었는데, 2번의 경우 길이가 너무 짧아 못풀었습니다.
제출한 답안 그대로 올릴겠습니다
1-1.
복구된 평문:
youneedtomanageyourresourcesspeednolongermattersitusedtobethecasethatprogramstookareallylongtimetoruncpuswereexpensivememorywasexpensiverunningtimeofaprogramusedtobeanimportantmetriccomputerswereveryexpensiveandsowastheelectricitytorunthemoptimizationoftheseresourceswasdonebecauseofaneternalbusinesslawoptimizeyourmostexpensiveresourcehistoricallythemostexpensiveresourcewascomputerruntimethisiswhatleadtothestudyofcomputersciencewhichfocusesonefficiencyofdifferentalgorithmshoweverthisisnolongertrueassiliconisnowcheaplikereallycheapruntimeisnolongeryourmostexpensiveresourceacompanysmostexpensiveresourceisnowitsemployeestimeorinotherwordsyouitsmoreimportanttogetstuffdonethantomakeitgofastinfactthisissoimportantiamgoingtoputitagainrighthereasifitwasaquoteforthosewhoarejustbrowsingitsmoreimportanttogetstuffdonethantomakeitgofastyoumightbesayingmycompanycaresaboutspeedibuildawebapplicationandallresponseshavetobefasterthanxmillisecondsorwehavehadcustomerscancelbecausetheythinkourappistooslowiamnottryingtosaythatspeeddoesntmatteratalliamsimplytryingtosaythatitsnolongerthemostimportantthingitsnotyourmostexpensiveresourcespeedspeedistheonlythingthatmatterswhenyousayspeedinthecontextofprogrammingyoutypicallymeanperformanceakacpucycleswhenyourceosaysspeedinthecontextofprogramminghemeansbusinessspeedthemostimportantmetricistimetomarketultimatelyitdoesntmatterhowfastyourproductwebappisitdoesntmatterwhatlanguageitswritteninitdoesntevenmatterhowmuchmoneyittakestorunattheendofthedaytheonethingthatwillmakeyourcompanysurviveordieistimetomarketimnotjusttalkingaboutthestartupideaofhowlongittakestillyoumakemoneybutmoresothetimeframeoffromideatocustomershandstheonlywaytosurviveinbusinessistoinnovatefasterthanyourcompetitorsitdoesntmatterhowmanygoodideasyoucomeupwithifyourcompetitorsshipbeforeyoudoyouhavetobethefirsttomarketoratleastkeepuponceyouslowdownyouaredonetheonlywaytosurviveinbusinessistoinnovatefasterthanyourcompetitorsacaseofmicroservicescompanieslikeamazongoogleandnetflixunderstandtheimportanceofmovingfasttheyhavecreatedabusinesssystemwheretheycanmovefastandinnovatequicklymicroservicesarethesolutiontotheirproblemthisarticlehasnothingtodowithwhetherornotyoushouldbeusingmicroservicesbutatleastacceptthatamazonandgooglethinktheyshouldbeusingthemmicroservicesareinherentlyslowtheveryconceptofamicroserviceistobreakupaboundarybyanetworkcallthismeansyouaretakingwhatwasafunctioncallacouplecpucyclesandturningitintoanetworkcallthereisntmuchyoucoulddothatisworseintermsofperformancenetworkcallsarereallyslowcomparedtothecpubutthesebigcompaniesstillchoosetousemicroservicestherereallyisntanarchitectureslowerthanmicroservicesthatiknowofmicroservicesbiggestconisperformancebutgreatestproistimetomarketbybuildingteamsaroundsmallerprojectsandcodebasesacompanyisabletoiterateandinnovateatamuchfasterpacethisjustgoestoshowthatverylargecompaniesalsocareabouttimetomarketnotjuststartupscpuisnotyourbottleneckifyouwriteanetworkapplicationsuchasawebserverchancesarecputimeisnotthebottleneckofyourapplicationwhenyourwebserverhandlesarequestitprobablymakesacouplenetworkcallssuchastoyourdatabaseorperhapsacacheserverlikerediswhiletheseservicesthemselvesmaybefastthenetworkcalltothemisslowthereisareallygreatblogarticleonthespeeddifferencesofcertainoperationsinthearticletheauthorscalescpucycletimesintomoreunderstandablehumantimesifasinglecpucyclewastheequivalentofonesecondthenanetworkcallfromcaliforniatonewyorkwouldbetheequivalentoffouryearsthatishowmuchslowernetworkisforsomeroughestimatesletssayanormalnetworkcallinsidethesamedatacentertakesaboutthreemsthatwouldbetheequivalentofthreemonthsinourhumanscalenowimagineyourprogramisverycpuintensiveittakesahundredthousandcyclestorespondtoasinglecallthatwouldbetheequivalentofjustoveronedaynowletssayyouusealanguagethatisfivetimesasslownowittakesaboutfivedayswellcomparethattoourthreemonthnetworkcallandthefourdaydifferencedoesntreallymattermuchatallifsomeonehastowaitatleastthreemonthsforapackageidontthinkanextrafourdayswillreallymatterallthatmuchtothemwhatthisultimatelymeansisthatevenifpythonisslowitdoesntmatterthespeedofthelanguageorcputimeisalmostnevertheissuegoogleactuallydidastudyonthisveryconceptandtheywroteapaperonitthepapertalksaboutdesigningahighthroughputsystemintheconclusiontheysayitmayseemparadoxicaltou
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시프트 값 : 13, 21
풀이:
테이블이 n번 움직인 후에는 초기의 테이블과 같은 모양을 띌 것으로 생각했다. 그리고 길이 n위치마다 있는 알파벳은 같은 키테이블로 암호화되기 때문에 일반적인 알파벳의 빈도를 따를 것으로 생각했다.
반복되는 길이를 추측하기 위해 암호문을 n의 길이로 나누고 같은 위치를 같은 문자끼리 합하였다.
그리고 index of coincidence를 계산하였다. 그 결과 키 길이(테이블이 처음과 같은 상태로 돌아오는 길이)에서 일반적인 알파벳의 index of coincidence값인 0.6정도가 나왔다.
이후 암호문을 26의 길이잡고 알파벳의 빈도를 분석하였다. 빈도 분석 후에 자주 사용되는 2글자, 3글자를 대입해봄으로써 비밀정보를 구할 수 있었다.
1-2.
답안:
문제 1-1과 같은 방법으로 접근하여 반복되는 길이가 26인 것은 확인하였으나. 그 외의 비밀정보는 찾지 못하였다. 1-1에 비해 주어진 데이터가 적어 구하기 못하였다.
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