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#!/usr/bin/perl
# https://perlweeklychallenge.org/blog/perl-weekly-challenge-015/
# Challenge #2
# Write a script to implement Vigen�re cipher.
# The script should be able encode and decode.
# Checkout wiki page for more information.
# https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher
use strict;
use warnings;
die "Usage: $0 <-e plaintext|-d ciphertext> <key>" unless (@ARGV == 3);
my $action = $ARGV[0];
if ($action eq '-e') {
print encode($ARGV[1],$ARGV[2]);
}
elsif ($action eq '-d') {
print decode($ARGV[1],$ARGV[2]);
}
else {
print "Valid actions are: -e (encode) or -d (decode)\n";
}
sub encode { vigenere(@_, 1) }
sub decode { vigenere(@_,-1) }
sub vigenere {
my $text = clean(shift);
my $key = clean(shift);
my $sign = shift;
my $repeat = int(length($text)/length($key))+1;
my $keyext = $key x $repeat; # repeat key string up to text length
my @letters = 'A' .. 'Z';
my %charcode = map { $letters[$_] => $_ } 0 .. 25;
my $plain = '';
foreach my $i (0 .. length($text)-1) {
# the magic begins: Vigen�re algebraically applied
$plain .= $letters[
( $charcode{substr($text,$i,1)}
+ $sign * $charcode{substr($keyext,$i,1)}
) % 26
];
}
return $plain;
}
sub clean {
my $text = shift;
$text =~ s/[^a-z]//gi; # remove non-alphabetic characters
return (uc $text); # uppercase characters
}
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