Vigenère cipher/Cryptanalysis: Difference between revisions
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Decrypted Text: THISWASTHEPOEMTHATALICEREADJABBERWOCKYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEBEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCHBEWARETHEJUBJUBBIRDANDSHUNTHEFRUMIOUSBANDERSNATCHHETOOKHISVORPALSWORDINHANDLONGTIMETHEMANXOMEFOEHESOUGHTSORESTEDHEBYTHETUMTUMTREEANDSTOODAWHILEINTHOUGHTANDASINUFFISHTHOUGHTHESTOODTHEJABBERWOCKWITHEYESOFFLAMECAMEWHIFFLINGTHROUGHTHETULGEYWOODANDBURBLEDASITCAMEONETWOONETWOANDTHROUGHANDTHROUGHTHEVORPALBLADEWENTSNICKERSNACKHELEFTITDEADANDWITHITSHEADHEWENTGALUMPHINGBACKANDHASTTHOUSLAINTHEJABBERWOCKCOMETOMYARMSMYBEAMISHBOYOFRABJOUSDAYCALLOOHCALLAYHECHORTLEDINHISJOYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEITSEEMSVERYPRETTYSHESAIDWHENSHEHADFINISHEDITBUTITSRATHERHARDTOUNDERSTAND |
Decrypted Text: THISWASTHEPOEMTHATALICEREADJABBERWOCKYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEBEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCHBEWARETHEJUBJUBBIRDANDSHUNTHEFRUMIOUSBANDERSNATCHHETOOKHISVORPALSWORDINHANDLONGTIMETHEMANXOMEFOEHESOUGHTSORESTEDHEBYTHETUMTUMTREEANDSTOODAWHILEINTHOUGHTANDASINUFFISHTHOUGHTHESTOODTHEJABBERWOCKWITHEYESOFFLAMECAMEWHIFFLINGTHROUGHTHETULGEYWOODANDBURBLEDASITCAMEONETWOONETWOANDTHROUGHANDTHROUGHTHEVORPALBLADEWENTSNICKERSNACKHELEFTITDEADANDWITHITSHEADHEWENTGALUMPHINGBACKANDHASTTHOUSLAINTHEJABBERWOCKCOMETOMYARMSMYBEAMISHBOYOFRABJOUSDAYCALLOOHCALLAYHECHORTLEDINHISJOYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEITSEEMSVERYPRETTYSHESAIDWHENSHEHADFINISHEDITBUTITSRATHERHARDTOUNDERSTAND |
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</pre> |
</pre> |
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=={{header|J}}== |
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Implementation: |
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<syntaxhighlight lang=J>NB. https://en.wikipedia.org/wiki/Kasiski_examination |
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kasiski=: {{ |
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grams=. ({: #"1~1 < ;@{.)|:(#/.~;"0~.) g=. 3 <\ y |
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deltas=. ;grams (2 -~/\ I.@E.)L:0 enc |
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{:,{.\:~(#/.~,.~.)1 -.~,+./~ deltas |
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}} |
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NB. https://en.wikipedia.org/wiki/Letter_frequency |
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AZ=: 8 u: 65+i.26 |
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lfreq=: 0.01*do{{)n |
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8.2 1.5 2.8 4.3 13 2.2 2 6.1 7 0.15 |
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0.77 4 2.4 6.7 7.5 1.9 0.095 6 6.3 9.1 |
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2.8 0.98 2.4 0.15 2 0.074 |
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}}-.LF |
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caesarkey=: {{ |
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freqs=. (<:#/.~AZ,y)%#y=. y ([-.-.) AZ |
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AZ{~(i. <./)lfreq +/&.:*:@:-"1 (i.26)|."0 1 freqs |
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}} |
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vigenerekey=: {{ caesarkey"1|:(-kasiski y) ]\y }} |
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uncaesar=: {{ 26&|@-&(AZ i.x)&.(AZ&i.) y }}"0 1 |
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unvigenere=: {{ ' '-.~,x uncaesar"0 1&.|:(-#x) ]\y }}</syntaxhighlight> |
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Task example: |
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<syntaxhighlight lang=J>enc=: {{)n |
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MOMUD EKAPV TQEFM OEVHP AJMII CDCTI FGYAG JSPXY ALUYM NSMYH |
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VUXJE LEPXJ FXGCM JHKDZ RYICU HYPUS PGIGM OIYHF WHTCQ KMLRD |
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ITLXZ LJFVQ GHOLW CUHLO MDSOE KTALU VYLNZ RFGBX PHVGA LWQIS |
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FGRPH JOOFW GUBYI LAPLA LCAFA AMKLG CETDW VOELJ IKGJB XPHVG |
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ALWQC SNWBU BYHCU HKOCE XJEYK BQKVY KIIEH GRLGH XEOLW AWFOJ |
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ILOVV RHPKD WIHKN ATUHN VRYAQ DIVHX FHRZV QWMWV LGSHN NLVZS |
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JLAKI FHXUF XJLXM TBLQV RXXHR FZXGV LRAJI EXPRV OSMNP KEPDT |
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LPRWM JAZPK LQUZA ALGZX GVLKL GJTUI ITDSU REZXJ ERXZS HMPST |
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MTEOE PAPJH SMFNB YVQUZ AALGA YDNMP AQOWT UHDBV TSMUE UIMVH |
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QGVRW AEFSP EMPVE PKXZY WLKJA GWALT VYYOB YIXOK IHPDS EVLEV |
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RVSGB JOGYW FHKBL GLXYA MVKIS KIEHY IMAPX UOISK PVAGN MZHPW |
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TTZPV XFCCD TUHJH WLAPF YULTB UXJLN SIJVV YOVDJ SOLXG TGRVO |
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SFRII CTMKO JFCQF KTINQ BWVHG TENLH HOGCS PSFPV GJOKM SIFPR |
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ZPAAS ATPTZ FTPPD PORRF TAXZP KALQA WMIUD BWNCT LEFKO ZQDLX |
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BUXJL ASIMR PNMBF ZCYLV WAPVF QRHZV ZGZEF KBYIO OFXYE VOWGB |
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BXVCB XBAWG LQKCM ICRRX MACUO IKHQU AJEGL OIJHH XPVZW JEWBA |
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FWAML ZZRXJ EKAHV FASMU LVVUT TGK |
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}}-.LF,' ' |
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vigenerekey enc |
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THECHESHIRECAT |
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_80]\'THECHESHIRECAT' unvigenere enc |
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THISWASTHEPOEMTHATALICEREADJABBERWOCKYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMB |
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LEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEBEWARETHEJABBERWOCKMYS |
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ONTHEJAWSTHATBITETHECLAWSTHATCATCHBEWARETHEJUBJUBBIRDANDSHUNTHEFRUMIOUSBANDERSNA |
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TCHHETOOKHISVORPALSWORDINHANDLONGTIMETHEMANXOMEFOEHESOUGHTSORESTEDHEBYTHETUMTUMT |
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REEANDSTOODAWHILEINTHOUGHTANDASINUFFISHTHOUGHTHESTOODTHEJABBERWOCKWITHEYESOFFLAM |
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ECAMEWHIFFLINGTHROUGHTHETULGEYWOODANDBURBLEDASITCAMEONETWOONETWOANDTHROUGHANDTHR |
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OUGHTHEVORPALBLADEWENTSNICKERSNACKHELEFTITDEADANDWITHITSHEADHEWENTGALUMPHINGBACK |
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ANDHASTTHOUSLAINTHEJABBERWOCKCOMETOMYARMSMYBEAMISHBOYOFRABJOUSDAYCALLOOHCALLAYHE |
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CHORTLEDINHISJOYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWER |
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ETHEBOROGOVESANDTHEMOMERATHSOUTGRABEITSEEMSVERYPRETTYSHESAIDWHENSHEHADFINISHEDIT |
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BUTITSRATHERHARDTOUNDERSTANDWYTWITSJWYAH |
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</syntaxhighlight> |
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As an aside, note that we could go directly from encrypted text to decrypted text, without showing the key. For example, using: |
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<syntaxhighlight lang=J>decaesar=: {{ |
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freqs=. (<:#/.~AZ,y)%#y=. y ([-.-.) AZ |
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ndx=. (i. <./)lfreq +/&.:*:@:-"1 (i.26)|."0 1 freqs |
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26&|@-&ndx&.(AZ&i.) y |
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}} |
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devigenere=: {{ ' '-.~,decaesar"1&.|:(-kasiski y) ]\y }}</syntaxhighlight> |
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That said, it's also worth noting that noise issues mean that if this were to be used in practical contexts the approach should instead be to expose more intermediate results, rather than less, with a special focus on the representations of frequency distributions (here, we're always picking the first alternative, but it's vaguely plausible that a different alternative might actually be useful in some cases). |
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=={{header|Java}}== |
=={{header|Java}}== |