rend_service_private_key_exists(const rend_service_t *service)
{
  char *private_key_path = rend_service_path(service, private_key_fname);
  const file_status_t private_key_status = file_status(private_key_path);
  tor_free(private_key_path);
  /* Only non-empty regular private key files could have been used before.
   * fstatus can be FN_ERROR if the service directory does not exist, in that
   * case, there is obviously no private key. */
  return private_key_status == FN_FILE;
}

The product writes sensitive information to a log file.