/usr/lib/x86_64-linux-gnu/libidn.so.11 is in libidn11 1.29-1+deb8u2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libidn.so.11.6.12
/usr/lib/x86_64-linux-gnu/libidn.so.11.6.12