<?php

function generate()   
{
      $code_length = 16;
      $characters = '0123456789abcdefghijklmnopqrstuvwxyz';

      for ($p = 0; $p < $code_length; $p++)
      {
          if (!($p % 4) && $p != 0)
              $string .= '-';

          $string .= $characters[rand(0, strlen($characters))];
      }

      return strtoUpper($string);
}

for ($i = 0; $i < 25; $i++)
{
      echo generate();
      echo "<br>";
}

?>