/usr/lib/x86_64-linux-gnu/libnfft3.so.1 is in libnfft3-1 3.2.3+dfsg-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnfft3.so.1.0.0
/usr/lib/x86_64-linux-gnu/libnfft3.so.1.0.0