#!/usr/bin/perl -w

use strict;

if( $#ARGV < 0 )
{
   die "$0 <key>\n";
}
my $key = shift;
$key =~ s/[^a-zA-Z]//g;
$key ||= "a";
my @offsets = map {$_ <= ord('Z') ? ord('A') - $_ + 26
                                  : $_ - ord('a')}
                  unpack 'C*', $key;

my $index = 0;
while( my $line = <> )
{
   foreach my $i (unpack 'C*', $line)
   {
      my $c = chr($i);
      if( $c =~ /[a-zA-Z]/ )
      {
         my $offset = $offsets[$index++];
         $index %= length($key);

         $c = ($c eq lc($c)) ? chr(($i - ord('a') + $offset) % 26 + ord('a'))
                             : chr(($i - ord('A') + $offset) % 26 + ord('A'));
      }
      print $c;
   }
}