How to resolve the algorithm Playfair cipher step by step in the J programming language

Published on 12 May 2024 09:40 PM
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How to resolve the algorithm Playfair cipher step by step in the J programming language

Table of Contents

Problem Statement

Implement a Playfair cipher for encryption and decryption.

The user must be able to choose   J  =  I     or   no   Q   in the alphabet. The output of the encrypted and decrypted message must be in capitalized digraphs, separated by spaces.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Playfair cipher step by step in the J programming language

Source code in the j programming language

choose=: verb define
  sel=. 'Q' e. y
  alph=: (sel { 'JQ') -.~ a. {~ 65 + i.26
  norm=: [: dedouble alph restrict ('I' I.@:=&'J'@]} ])`(-.&'Q')@.sel@toupper
  ''
)

restrict=: ] -. -.~

splitDigraph=: ,`([,'X',])@.((= {.) *. 2 | #@])
dedouble=: splitDigraph/&.|.                     NB. progressively split digraphs in string

choose 'Q'
 
setkey=: verb define
  key=. ~.norm y,alph
  ref=: ,/ 2{."1 ~."1 (,"0/~ alph) ,"1 norm 'XQV'
  mode=. #. =/"2 inds=. 5 5#:key i. ref
  inds0=. (0 3,:2 1)&{@,"2 inds
  inds1=. 5|1 0 +"1 inds NB. same column
  inds2=. 5|0 1 +"1 inds NB. same row
  alt=: key {~ 5 #. mode {"_1 inds0 ,"2 3 inds1 ,:"2 inds2
  i. 0 0
)
 
pairs=: verb define 
  2{."1 -.&' '"1 ~."1 (_2]\ norm y) ,"1 'XQV'
)
 
encrypt=: verb define
  ;:inv ;/ alt{~ref i. pairs y
)
 
decrypt=: verb define
  , ref{~alt i. pairs y
)


   choose 'IJ'

   setkey 'playfair example'
   encrypt 'Hide the gold in the tree stump'
BM OD ZB XD NA BE KU DM UI XM MO UV IF
   decrypt 'BM OD ZB XD NA BE KU DM UI XM MO UV IF'
HIDETHEGOLDINTHETREXESTUMP

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