code: public function encodeString($string)
      {
          $string=strtolower($string);
          $src="abcdefghijklmnopqrstuvwxyz0123456789 ";
          $dst="jklmnopqrstuvwxyz0123456789abcdefghi ";
          for ($i=0; $i<strlen($string); $i++) {
              $pos=strpos($src, $string[$i]);
              if ($pos===false) {
                  throw new \Exception("Please provide only numbers and alphanumerical characters");
              }
              $string[$i]=$dst[$pos];
          }
          return $string;
      }
docs: Encodes a string by a simple shift of characters
  
  @param string $string
  @return string
  @throws \Exception