The easiest way to recover or mount an off-line ecryptfs directory is the built-in command from ecryptfs
sudo ecryptfs-recover-private It will find your wrapped passphrase and ask for your password and mount it in tmp. Much easier especially when your current active OS is using ecryptfs too.
This a fantastic tool when going through old backups.........
ecryptfs-mount-private
Enter your login passphrase:
Inserted auth tok with sig [ee16d84] "into the user session keyring
mount: No such file or directory"
[ 156.118113] ecryptfs_mount: kern_path() failed
[ 156.118431] Reading sb failed; rc = [-2]
[ 164.233055] traps: mate-notificati[3472] trap int3 ip:7f43d7002c13 sp:7fff162c6600 error:0
[ 166.017061] ecryptfs_mount: kern_path() failed........