$ sudo ecryptfs-add-passphrase --fnek
Which gets me the following information:
Inserted auth tok with sig [aaaaaaaaaaaaaaaa] into the user session keyring
Inserted auth tok with sig [bbbbbbbbbbbbbbbb] into the user session keyring
$ sudo mount -t ecryptfs /media/user/66fa2d20-bb6a-231b-9a98-deac52c9282f/.ecryptfs/user/.Private /mnt/backup
A lot of questions pop up. Answer with their defaults except for
Enable filename encryption (y/n) [n]: y
Here paste the signature which has been shown before:
Filename Encryption Key (FNEK) Signature [aaaaaaaaaaaaaaaa]: bbbbbbbbbbbbbbbb
$ sudo umount /mnt/backup