use strict;
use warnings;


sub getcryptkey {
   return 'ABCDEFGHIJK';
}


{
   ##### WRITER #####

   my @records = (
      [ 0, 1, 2 ],
      [ 3, 4, 5 ],
      [ 6, 7, 8 ],
   );

   my $newenckey = getcryptkey();

   local *PASSF;
   open(PASSF, ">$ENV{HOME}/.perlpasswd")
   or die("Can't write $ENV{HOME}/.perlpasswd: $!\n");

   binmode(PASSF);

   my $buf = '';

   foreach (@records) {
      # Might want to use FreezeThaw instead.
      $buf .= "$_->[0] $_->[1] $_->[2]\n"; 

      print PASSF
         substr($buf, 0, length($newenckey), '') ^ $newenckey
            while (length($buf) >= length($newenckey));
   }

   print PASSF $buf ^ substr($newenckey, 0, length($buf));

   close(PASSF);
}

{
   ##### READER #####

   my @records;

   my $newenckey = getcryptkey();

   local *PASSF;
   open(PASSF, "<$ENV{HOME}/.perlpasswd")
   or die("Can't read $ENV{HOME}/.perlpasswd: $!\n");

   binmode(PASSF);

   my $buf_e = '';
   my $buf_d = '';

   my $BLOCK_SIZE = length($newenckey); # Can be anything.

   while (sysread(PASSF, $buf_e, $BLOCK_SIZE, length($buf_e))) {

      $buf_d .= substr($buf_e, 0, length($newenckey), '') ^ $newenckey
         while (length($buf_e) >= length($newenckey));
     
      push(@records, [ $1, $2, $3 ])
         while ($buf_d =~ s/^(\S+)\s+(\S+)\s+(\S+)\n//s);
   }

   $buf_d .= $buf_e ^ substr($newenckey, 0, length($buf_e));
     
   push(@records, [ $1, $2, $3 ])
      while ($buf_d =~ s/^(\S+)\s+(\S+)\s+(\S+)\n//s);

   close(PASSF);

   require Data::Dumper;
   print(Data::Dumper::Dumper(\@records));
}

__END__
##### OUTPUT #####

$VAR1 = [
          [
            '0',
            '1',
            '2'
          ],
          [
            '3',
            '4',
            '5'
          ],
          [
            '6',
            '7',
            '8'
          ]
        ];