How to resolve the algorithm Vigenère cipher/Cryptanalysis step by step in the J programming language

Published on 12 May 2024 09:40 PM
#J

How to resolve the algorithm Vigenère cipher/Cryptanalysis step by step in the J programming language

Table of Contents

Problem Statement

Given some text you suspect has been encrypted with a Vigenère cipher, extract the key and plaintext. There are several methods for doing this. See the Wikipedia entry for more information. Use the following encrypted text: Letter frequencies for English can be found here. Specifics for this task:

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Vigenère cipher/Cryptanalysis step by step in the J programming language

Source code in the j programming language

NB. https://en.wikipedia.org/wiki/Kasiski_examination
kasiski=: {{ 
  grams=. ({: #"1~1 < ;@{.)|:(#/.~;"0~.) g=. 3 <\ y
  deltas=. ;grams (2 -~/\ I.@E.)L:0 enc
  {:,{.\:~(#/.~,.~.)1 -.~,+./~ deltas
}}

NB. https://en.wikipedia.org/wiki/Letter_frequency
AZ=: 8 u: 65+i.26
lfreq=: 0.01*do{{)n
 8.2 1.5 2.8 4.3 13 2.2 2 6.1 7 0.15
 0.77 4 2.4 6.7 7.5 1.9 0.095 6 6.3 9.1
 2.8 0.98 2.4 0.15 2 0.074
}}-.LF


caesarkey=: {{
  freqs=. (<:#/.~AZ,y)%#y=. y ([-.-.) AZ
  AZ{~(i. <./)lfreq +/&.:*:@:-"1 (i.26)|."0 1 freqs
}}
vigenerekey=: {{ caesarkey"1|:(-kasiski y) ]\y }}

uncaesar=: {{ 26&|@-&(AZ i.x)&.(AZ&i.) y }}"0 1
unvigenere=: {{ ' '-.~,x uncaesar"0 1&.|:(-#x) ]\y }}


enc=: {{)n
MOMUD EKAPV TQEFM OEVHP AJMII CDCTI FGYAG JSPXY ALUYM NSMYH
VUXJE LEPXJ FXGCM JHKDZ RYICU HYPUS PGIGM OIYHF WHTCQ KMLRD
ITLXZ LJFVQ GHOLW CUHLO MDSOE KTALU VYLNZ RFGBX PHVGA LWQIS
FGRPH JOOFW GUBYI LAPLA LCAFA AMKLG CETDW VOELJ IKGJB XPHVG
ALWQC SNWBU BYHCU HKOCE XJEYK BQKVY KIIEH GRLGH XEOLW AWFOJ
ILOVV RHPKD WIHKN ATUHN VRYAQ DIVHX FHRZV QWMWV LGSHN NLVZS
JLAKI FHXUF XJLXM TBLQV RXXHR FZXGV LRAJI EXPRV OSMNP KEPDT
LPRWM JAZPK LQUZA ALGZX GVLKL GJTUI ITDSU REZXJ ERXZS HMPST
MTEOE PAPJH SMFNB YVQUZ AALGA YDNMP AQOWT UHDBV TSMUE UIMVH
QGVRW AEFSP EMPVE PKXZY WLKJA GWALT VYYOB YIXOK IHPDS EVLEV
RVSGB JOGYW FHKBL GLXYA MVKIS KIEHY IMAPX UOISK PVAGN MZHPW
TTZPV XFCCD TUHJH WLAPF YULTB UXJLN SIJVV YOVDJ SOLXG TGRVO
SFRII CTMKO JFCQF KTINQ BWVHG TENLH HOGCS PSFPV GJOKM SIFPR
ZPAAS ATPTZ FTPPD PORRF TAXZP KALQA WMIUD BWNCT LEFKO ZQDLX
BUXJL ASIMR PNMBF ZCYLV WAPVF QRHZV ZGZEF KBYIO OFXYE VOWGB
BXVCB XBAWG LQKCM ICRRX MACUO IKHQU AJEGL OIJHH XPVZW JEWBA
FWAML ZZRXJ EKAHV FASMU LVVUT TGK
}}-.LF,' '

   vigenerekey enc
THECHESHIRECAT
   _80]\'THECHESHIRECAT' unvigenere enc
THISWASTHEPOEMTHATALICEREADJABBERWOCKYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMB
LEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEBEWARETHEJABBERWOCKMYS
ONTHEJAWSTHATBITETHECLAWSTHATCATCHBEWARETHEJUBJUBBIRDANDSHUNTHEFRUMIOUSBANDERSNA
TCHHETOOKHISVORPALSWORDINHANDLONGTIMETHEMANXOMEFOEHESOUGHTSORESTEDHEBYTHETUMTUMT
REEANDSTOODAWHILEINTHOUGHTANDASINUFFISHTHOUGHTHESTOODTHEJABBERWOCKWITHEYESOFFLAM
ECAMEWHIFFLINGTHROUGHTHETULGEYWOODANDBURBLEDASITCAMEONETWOONETWOANDTHROUGHANDTHR
OUGHTHEVORPALBLADEWENTSNICKERSNACKHELEFTITDEADANDWITHITSHEADHEWENTGALUMPHINGBACK
ANDHASTTHOUSLAINTHEJABBERWOCKCOMETOMYARMSMYBEAMISHBOYOFRABJOUSDAYCALLOOHCALLAYHE
CHORTLEDINHISJOYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWER
ETHEBOROGOVESANDTHEMOMERATHSOUTGRABEITSEEMSVERYPRETTYSHESAIDWHENSHEHADFINISHEDIT
BUTITSRATHERHARDTOUNDERSTANDWYTWITSJWYAH


decaesar=: {{
  freqs=. (<:#/.~AZ,y)%#y=. y ([-.-.) AZ
  ndx=. (i. <./)lfreq +/&.:*:@:-"1 (i.26)|."0 1 freqs
  26&|@-&ndx&.(AZ&i.) y
}}
devigenere=: {{ ' '-.~,decaesar"1&.|:(-kasiski y) ]\y }}

You may also check:How to resolve the algorithm SEDOLs step by step in the Common Lisp programming language
You may also check:How to resolve the algorithm Hello world/Newline omission step by step in the 11l programming language
You may also check:How to resolve the algorithm SEDOLs step by step in the AWK programming language
You may also check:How to resolve the algorithm Non-continuous subsequences step by step in the Perl programming language
You may also check:How to resolve the algorithm Singleton step by step in the Perl programming language