update pycryptodomex requirement

requirements.txt

@@ -4,7 +4,7 @@ tornado==6.4.1  # http://www.tornadoweb.org/en/stable/releases.html
 psycopg2==2.9.10  # http://initd.org/psycopg/articles/tag/release/
 sqlalchemy>=1.3,<1.4  # http://docs.sqlalchemy.org/en/latest/changelog/index.html
 netifaces>=0.10,<0.11  # https://bitbucket.org/al45tair/netifaces/src/
-pycryptodomex>=3.6,<3.7  # https://github.com/Legrandin/pycryptodome/blob/master/Changelog.rst
+pycryptodomex==3.21.0  # https://github.com/Legrandin/pycryptodome/blob/master/Changelog.rst
 psutil==5.9.8  # https://github.com/giampaolo/psutil/blob/master/HISTORY.rst
 requests>=2.22,<2.23  # https://pypi.python.org/pypi/requests
 gevent==24.10.2  # http://www.gevent.org/changelog.html