/usr/lib/ipsec/libpttls.so is in libcharon-extra-plugins 5.5.1-4+deb9u4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ipsec/libpttls.so.0.0.0
/usr/lib/ipsec/libpttls.so.0.0.0