code: static function getRandomBytes($numBytes)
      {
          Checker::argIntPositive("numBytes", $numBytes);
  
          // openssl_random_pseudo_bytes had some issues prior to PHP 5.3.4
          if (function_exists('openssl_random_pseudo_bytes')
                  && version_compare(PHP_VERSION, '5.3.4') >= 0) {
              $s = openssl_random_pseudo_bytes($numBytes, $isCryptoStrong);
              if ($isCryptoStrong) return $s;
          }
  
          if (function_exists('mcrypt_create_iv')) {
              return mcrypt_create_iv($numBytes);
          }
  
          // Hopefully the above two options cover all our users.  But if not, there are
          // other platform-specific options we could add.
          throw new \Exception("no suitable random number source available");
      }
docs: Returns cryptographically strong secure random bytes (as a PHP string).
  
  @param int $numBytes
  The number of bytes of random data to return.
  
  @return string