How to resolve the algorithm Substitution cipher step by step in the Picat programming language

Published on 12 May 2024 09:40 PM
#Picat

How to resolve the algorithm Substitution cipher step by step in the Picat programming language

Table of Contents

Problem Statement

Substitution Cipher Implementation - File Encryption/Decryption

Encrypt an input/source file by replacing every upper/lower case alphabets of the source file with another predetermined upper/lower case alphabets or symbols and save it into another output/encrypted file and then again convert that output/encrypted file into original/decrypted file. This type of Encryption/Decryption scheme is often called a Substitution Cipher.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Substitution cipher step by step in the Picat programming language

Source code in the picat programming language

main =>
  S = "The quick brown fox jumped over the lazy dog",
  cypher(S,E),  % encrypt
  println(E),

  cypher(D, E), % decrypt
  println(D),

  S == D,
  println(ok).

cypher(O, S) :-
  nonvar(O),
  var(S),
  sub_chars(O,S).
cypher(O, S) :-
  nonvar(S),
  var(O),
  sub_chars(O,S).

base("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz ").
subs("VsciBjedgrzyHalvXZKtUPumGfIwJxqOCFRApnDhQWob LkESYMTN").
 
sub_chars(Original,Subbed) :-
  base(Base),
  subs(Subs),
  maplist($sub_char(Base,Subs),Original,Subbed).

sub_char([Co|_],[Cs|_],Co,Cs) :- !.
sub_char([_|To],[_|Ts], Co, Cs) :- sub_char(To,Ts,Co,Cs).

maplist(Goal, List1, List2) :-
    maplist_(List1, List2, Goal).

maplist_([], X, _) :- X = []. 
maplist_([Elem1|Tail1],
         [Elem2|Tail2],
         Goal) :-
    call(Goal, Elem1, Elem2),
    maplist_(Tail1, Tail2, Goal).

main =>
  S = "The quick brown fox jumped over the lazy dog!!!",
  E = encrypt(S),
  println(E),
  D = decrypt(E),
  println(D),

  D == S,
  println(ok),
  nl.

encrypt(L) = [EncryptMap.get(C,C) : C in L] =>
  base(Base),
  subs(Subs),
  EncryptMap = new_map([B=S : {B,S} in zip(Base,Subs)]).

decrypt(L) = [DecryptMap.get(C,C) : C in L] =>
  base(Base),
  subs(Subs),
  DecryptMap = new_map([S=B : {B,S} in zip(Base,Subs)]).

base("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz ").
subs("VsciBjedgrzyHalvXZKtUPumGfIwJxqOCFRApnDhQWob LkESYMTN").

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