/usr/lib/ipsec/libnttfft.so.0 is in libstrongswan-extra-plugins 5.6.2-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ipsec/libnttfft.so.0.0.0
/usr/lib/ipsec/libnttfft.so.0.0.0