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#!/usr/bin/env perl
#
# Write a script to implement Vigenère cipher.
# (https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher)
################################################################################
use strict;
use warnings;
sub vigenere {
# Direction: encrypt (1) vs decrypt (-1)
my ($direction, $text, $key) = @_;
chomp $text;
my ($A, $Z) = (ord("a"), ord("z"));
my $OFFSET = $Z - $A + 1;
foreach my $i (0 .. length($text)-1) {
# Only process alpha characters (gets lowered before)
next unless substr($text, $i, 1) =~ /^[a-zA-Z]$/;
# Add/subtract the key character to the corresponding one in text
my $ord = ord(lc(substr($text, $i, 1))) +
$direction * (ord(substr($key, $i % length($key), 1)) - $A);
# Adjust if character got out of alpha range
$ord -= $OFFSET if $ord > $Z;
$ord += $OFFSET if $ord < $A;
substr($text, $i, 1) = chr($ord);
}
return $text;
}
sub encrypt { vigenere(1, @_); }
sub decrypt { vigenere(-1, @_); }
my $USAGE = "Usage: $0 (enc|dec) key\n";
my $MODE = shift or die $USAGE;
my $KEY = shift or die $USAGE;
my $f;
if ($MODE eq "enc") {
$f = \&encrypt;
} elsif ($MODE eq "dec") {
$f = \&decrypt;
} else {
die $USAGE;
}
while (<STDIN>) {
print $f->($_, $KEY), "\n";
}
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