/usr/share/doc/strongswan-plugin-ipseckey/changelog.Debian.gz is in strongswan-plugin-ipseckey 5.1.2-0ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/strongswan-plugin-ipseckey/../libstrongswan/changelog.Debian.gz