* ``urwid`` is an optional dependency used for :ref:`interactive browser <browser>`.
* ``dateutil`` is an optional dependency used for ``.totzdatetime()`` method.
-You could use pip (**no** OpenPGP authentication is performed!) with PyPI::
-
- $ echo pyderasn==9.3 --hash=sha256:TO-BE-FILLED > requirements.txt
- $ pip install --requirement requirements.txt
-
You have to verify downloaded tarballs integrity and authenticity to be
sure that you retrieved trusted and untampered software. `GNU Privacy
Guard <https://www.gnupg.org/>`__ is used for that purpose.