Mounting Encrypted Home Directories
Unwrap the old passphrase to get the mount passphrase:
ecryptfs-unwrap-passphrase /old/.ecryptfs/user/wrapped-passphrase
Generate the kernel session keys:
ecryptfs-add-passphrase --fnek
The value in brackets on the second line is the one to remember.
Now mount the .Private directory:
mount -t ecryptfs /old/.ecryptfs/user/.Private /mnt/old
As passphrase enter the mount passphrase from above. Choose aes, 16, answer no to plaintext passthrough, yes to filename encryption and entry the value I told you to remember earlier.
Done.