simple token algorithm with PHP

function uid($n, $len1=5, $len2=15, $base=36)
  {
    $id_part = base_convert($n, 10, $base);
    $rand_part = str_shuffle('abcdefghijklmnopqrstuvwxyz0123456789');
    return sprintf("%0".$len1."s-%.".$len2."s", $id_part, $rand_part);
  }   

source: http://stackoverflow.com/questions/2377633/how-create-an-unique-20-single-byte-token-key-id-on-php