Vigenère cipher/Cryptanalysis: Difference between revisions
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Decrypted Text: THISWASTHEPOEMTHATALICEREADJABBERWOCKYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEBEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCHBEWARETHEJUBJUBBIRDANDSHUNTHEFRUMIOUSBANDERSNATCHHETOOKHISVORPALSWORDINHANDLONGTIMETHEMANXOMEFOEHESOUGHTSORESTEDHEBYTHETUMTUMTREEANDSTOODAWHILEINTHOUGHTANDASINUFFISHTHOUGHTHESTOODTHEJABBERWOCKWITHEYESOFFLAMECAMEWHIFFLINGTHROUGHTHETULGEYWOODANDBURBLEDASITCAMEONETWOONETWOANDTHROUGHANDTHROUGHTHEVORPALBLADEWENTSNICKERSNACKHELEFTITDEADANDWITHITSHEADHEWENTGALUMPHINGBACKANDHASTTHOUSLAINTHEJABBERWOCKCOMETOMYARMSMYBEAMISHBOYOFRABJOUSDAYCALLOOHCALLAYHECHORTLEDINHISJOYTWASBRILLIGANDTHESLITHYTOVESDIDGYREANDGIMBLEINTHEWABEALLMIMSYWERETHEBOROGOVESANDTHEMOMERATHSOUTGRABEITSEEMSVERYPRETTYSHESAIDWHENSHEHADFINISHEDITBUTITSRATHERHARDTOUNDERSTAND
</pre>
=={{header|J}}==
Implementation:
<syntaxhighlight lang=J>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 }}</syntaxhighlight>
Here, kasiski finds all 3-grams (sequences of three adjacent letters) which appear more than once, finds all of the distances between nearest pairs of these sequences, and then further pairs each of these distances with all other distances, finding the greatest common divisor of those distance pairs. Finally, these LCDs are ordered by how many times they appear and the most frequent LCD is taken as the kasiski result.
uncaesar works by finding the frequency of occurrence of each letter of the alphabet (in alphabetical order), and then each of the 26 rotations of that sequence are compared with a text frequency alphabet (obtained from a wikipedia table). The rotation with the least root-mean-square sum of differences is chosen as the correct location, and its index is reported as a letter of the alphabet (0=A, 1=B, etc.)
(And, the length provided by kasiski is used to break out the sequences to be analyzed by uncaesar...)
Task example:
<syntaxhighlight lang=J>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
</syntaxhighlight>
As an aside, note that we could go directly from encrypted text to decrypted text, without showing the key. For example, using:
<syntaxhighlight lang=J>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 }}</syntaxhighlight>
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).
=={{header|Java}}==
Line 3,272 ⟶ 3,354:
{{trans|Kotlin}}
{{libheader|Wren-math}}
{{libheader|Wren-
{{libheader|Wren-str}}
{{libheader|Wren-fmt}}
<syntaxhighlight lang="
import "./
import "./str" for Char, Str
import "./fmt" for Fmt
var encoded =
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