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[Powered by Google Translate] [Vigenère Cipher]

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[Nate Hardison - Chuo Kikuu cha Harvard]

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[Hii ni CS50. - CS50.TV]

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Kutana Alice.

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Alice ana kuponda juu Bob.

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Bahati nzuri kwa Alice, Bob pia ana macho kwa ajili yake.

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Bahati mbaya kwa mpenzi yao budding,

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si tu kufanya Alice wazazi onya Bob,

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lakini Alice bora rafiki, Evelyn, ina kuponda siri juu ya Bob

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na ubinafsi anataka kuweka peke yao kwa gharama zote.

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Ili kutuma ujumbe wa siri na kila mmoja kuwa Alice wazazi hawawezi kuelewa,

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>> Alice na Bob wamekuwa wakitumia cipher Kaisari,

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ambayo hufanya kazi kwa shifting alfabeti na idadi fulani ya barua

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kama njia ya kuzalisha alfabeti mpya.

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Kila barua katika alfabeti ya awali ni kisha kubadilishwa kwa barua yake sambamba

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katika alfabeti mpya kubadilishwa.

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Alice namba favorite ni 3, ambayo Bob anajua,

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hivyo yeye anatumia 3 kama ufunguo wake.

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Wakati yeye mabadiliko alfabeti ya Kiingereza na herufi 3,

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inakuwa D, B inakuwa E, C inakuwa F,

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na kadhalika.

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>> Wakati yeye anapata hadi mwisho wa alfabeti - kwa barua X, Y, na Z -

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yeye tu Wraps kuzunguka nyuma mwanzo wa alfabeti

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na substitutes X Y, na B, na Z na C.

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Hivyo wakati Alice huenda encrypt ujumbe wake siri na Bob,

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yaani "Meet yangu katika Hifadhi ya saa kumi na moja var kl,"

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yeye tu hufanya substitutions mwafaka.

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M inakuwa P, E inakuwa H, na kadhalika mpaka wake kimaandishi Nakala wazi ujumbe

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yamegeuka Nakala encrypted cipher:

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"Phhw ph DW wkh sdun DW hohyhq DP"

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ni dhahiri si sounding kimapenzi zaidi,

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lakini Alice kuamini kwamba itabidi kufanya.

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>> Alice anatoa ujumbe kwa Evelyn wa kutoa na nyumba Bob.

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Lakini Evelyn badala inachukua nyuma kwa nafasi yake na inajaribu ufa code.

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Moja ya mambo ya kwanza Evelyn matangazo ni kwamba H barua hutokea mara 7 katika ujumbe,

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wengi zaidi kuliko nyakati barua nyingine yoyote.

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Kujua kwamba E barua ni ya kawaida katika lugha ya Kiingereza,

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zinazotokea karibu 13% ya muda,

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Evelyn guesses kwamba H imekuwa kubadilishwa kwa E ili kufanya ujumbe siri

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na anajaribu kutumia ufunguo wa 3 ili kuisimbua.

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>> Ndani ya dakika, Evelyn takwimu nje mipango Alice na evilly wito wazazi Alice ya.

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Lau Alice na Bob kuchukuliwa CS50, wangeli inayojulikana ya hii

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frequency-uchambuzi mashambulizi cipher Kaisari,

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ambayo inaruhusu kuwa ni kuvunjwa kabisa haraka.

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Wao pia tunajua kwamba cipher ni urahisi chini ya mashambulizi brute-nguvu,

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ambapo Evelyn inaweza wamejaribu yote ya funguo iwezekanavyo 25,

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au mabadiliko ya alfabeti ya Kiingereza,

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ili decipher ujumbe.

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Kwa nini 25 funguo na si 26?

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>> Naam, jaribu shifting barua yoyote kwa nafasi 26, na utaona nini.

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Anyway, mashambulizi brute-nguvu kuyang Evelyn kidogo tena

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lakini si muda mrefu wa kutosha kutunza yake kutoka thwarting Alice na mipango Bob,

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hasa kama Evelyn ana misaada ya kompyuta

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ambayo inaweza mpasuko kupitia kesi zote 25 katika papo.

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Hivyo, tatizo hili pia wanakumbana wengine ambao kutumika cipher Kaisari,

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na kwa hiyo watu walianza majaribio na ciphers ngumu zaidi badala

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kwamba matumizi ya maadili kuhama nyingi badala ya moja tu.

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Moja ya wengi anajulikana ya hizi inaitwa Vigenère cipher.

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Jinsi gani sisi kupata maadili kuhama nyingi?

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Naam, badala ya kutumia idadi kama ufunguo, sisi kutumia neno kwa ajili ya muhimu.

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Tutaweza kutumia kila barua katika ufunguo wa kuzalisha idadi,

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na athari ni kwamba tutaweza kuwa na nyingi Kaisari funguo cipher-style kwa shifting barua.

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>> Hebu angalia jinsi hii matendo na encrypting ujumbe Alice kwa Bob:

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Kukutana na mimi katika Hifadhi ya saa 11:00

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Mimi, binafsi, nadhani Bacon ni ladha,

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hivyo hebu kutumia kama muhimu.

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Kama sisi kuchukua ujumbe katika muundo wake kimaandishi, wazi-maandishi,

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tunaona kwamba ni 25 barua kwa muda mrefu.

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Bacon ina barua tu 5, hivyo tunahitaji kurudia mara 5

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kufanya hivyo mechi ya urefu wa Nakala wazi.

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>> Bacon Bacon Bacon Bacon Bacon.

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Kama kifupi kando, ikiwa idadi ya herufi katika Nakala wazi

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hawakuwa kugawanya cleanly na idadi ya herufi katika muhimu,

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sisi tu kumaliza marudio ya mwisho ya ufunguo yetu mapema,

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kutumia tu barua sisi zinahitajika ili kufanya kila kitu match up.

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Sasa sisi kwenda juu ya kutafuta maadili kuhama.

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>> Sisi wanaenda kufanya hivyo kwa kutumia nafasi ya kila barua ya ufunguo yetu - Bacon -

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katika A kwa alfabeti Z.

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Tangu sisi ni kompyuta wanasayansi, sisi kama kuanza kuhesabu saa sifuri badala ya 1,

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hivyo sisi ni kwenda kusema kwamba msimamo wa barua ya kwanza ya Bacon - B -

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ni katika nafasi ya 1 katika sifuri-indexed kwa alfabeti Z,

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si 2, na msimamo wa ni sifuri, si 1.

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Kutumia algorithm hii, tunaweza kupata maadili kuhama kwa kila herufi.

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>> Encrypt Nakala wazi na kuzalisha cipher maandishi,

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sisi tu kuhama kila barua katika Nakala wazi kwa kiasi fulani,

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tu kama sisi kufanya na cipher Kaisari, wrapping kutoka Z nyuma kama ni lazima.

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M anapata kubadilishwa na mahali 1 kuwa N.

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Barua ya kwanza haina kuhama wakati wote, lakini sisi kuhama E pili na maeneo 2 kwa G

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na T na maeneo 14 H.

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Kama sisi kazi kwa njia ya maandishi wazi, sisi kuishia na,

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"Negh ZF Av HUF pcfx bt gzrwep oz."

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Tena, si sana kimapenzi-sounding lakini dhahiri cryptic.

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Kama Alice na Bob angejua kuhusu Vigenère cipher,

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ingekuwa wamekuwa salama kutoka macho Evelyn wa prying?

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Unafikiri?

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Je, unataka kuingia katika akaunti yako ya benki kama benki yako aliamua kutumia

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>> Vigenère cipher encrypt mawasiliano yako kwa kutumia nywila yako kama ufunguo wako?

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Kama ningekuwa wewe, napenda.

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Na wakati Evelyn inaweza kuwekwa busy muda wa kutosha kwa Alice na Bob kuwa wao kukutana-up,

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siyo thamani yake kwa Alice na Bob kwa nafasi yake.

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Vigenère cipher ni rahisi kuvunja kama unajua urefu wa muhimu

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kwa sababu kisha unaweza kutibu encrypted cipher Nakala

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kama bidhaa ya ciphers chache interwoven Kaisari.

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>> Kupata urefu wa muhimu si sana ngumu, aidha.

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Kama awali wazi-ujumbe wa maandishi ni muda wa kutosha kwamba baadhi ya maneno kutokea mara nyingi,

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hatimaye utaona marudio mseto juu katika maandishi encrypted cipher,

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kama katika mfano huu, ambapo unaona MONCY itaonekana mara mbili.

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Zaidi ya hayo, unaweza kufanya mashambulizi brute-nguvu juu ya cipher.

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Hii haina kuchukua kiasi kikubwa zaidi ya mashambulizi brute-nguvu juu ya cipher Kaisari,

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ambayo inaweza kufanyika karibu mara kwa kompyuta

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tangu badala ya 25 kesi ya kuangalia nimepata 26 ⁿ - 1 uwezekano,

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ambapo n ni urefu wa ufunguo haijulikani.

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>> Hii ni kwa sababu kila barua katika muhimu inaweza kuwa yoyote ya barua 26,

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kupitia Z, na mtu smart ingekuwa kujaribu kutumia ufunguo kwamba hawezi kupatikana katika kamusi,

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ambayo ina maana kwamba wewe d na kupima yote ya mchanganyiko weird barua, kama ZXXXFF,

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na si tu wanandoa laki maneno katika kamusi.

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bala 1 anakuja katika math kwa sababu wewe si unataka kutumia ufunguo na tu ndiyo,

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tangu kwa alfabeti yetu sifuri-indexed kwamba bila kutoa athari sawa

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kama kutumia cipher Kaisari na muhimu ya sifuri.

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Anyway, 26 ⁿ - 1 haina kupata kubwa badala haraka,

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lakini wakati wewe dhahiri si unataka kujaribu kuvunja cipher kwa mkono kwa njia hii,

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hii ni dhahiri doable na kompyuta.

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Bahati nzuri kwa Alice na Bob, na kwa online benki,

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cryptographers kuwa na maendeleo ya njia salama zaidi kwa encrypt ujumbe siri

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kutoka macho prying.

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>> Hata hivyo, hiyo ni mada kwa wakati mwingine.

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Jina langu ni Nate Hardison. Hii ni CS50.