/usr/lib/python3/dist-packages/twisted/cred/ is in python3-twisted 16.6.0-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/python3/dist-packages/twisted/cred/__init__.py
/usr/lib/python3/dist-packages/twisted/cred/_digest.py
/usr/lib/python3/dist-packages/twisted/cred/checkers.py
/usr/lib/python3/dist-packages/twisted/cred/credentials.py
/usr/lib/python3/dist-packages/twisted/cred/error.py
/usr/lib/python3/dist-packages/twisted/cred/portal.py
/usr/lib/python3/dist-packages/twisted/cred/strcred.py
/usr/lib/python3/dist-packages/twisted/cred/test/
/usr/lib/python3/dist-packages/twisted/cred/test/__init__.py
/usr/lib/python3/dist-packages/twisted/cred/test/test_cramauth.py
/usr/lib/python3/dist-packages/twisted/cred/test/test_cred.py
/usr/lib/python3/dist-packages/twisted/cred/test/test_digestauth.py
/usr/lib/python3/dist-packages/twisted/cred/test/test_simpleauth.py
/usr/lib/python3/dist-packages/twisted/cred/test/test_strcred.py