تجربهای ندارم، اما گویا از ابزار ecryptfs-recover-private باید استفاده کنید.
http://manpages.ubuntu.com/manpages/zesty/en/man1/ecryptfs-recover-private.1.html (http://manpages.ubuntu.com/manpages/zesty/en/man1/ecryptfs-recover-private.1.html)
http://blog.dustinkirkland.com/2011/04/introducing-ecryptfs-recover-private.html (http://blog.dustinkirkland.com/2011/04/introducing-ecryptfs-recover-private.html)
http://pfertyk.me/2017/05/recovering-encrypted-home-directory-in-ubuntu/ (http://pfertyk.me/2017/05/recovering-encrypted-home-directory-in-ubuntu/)