Encrypted external disk, with no need to enter password each time

Question

There are many solutions to encrypt an external disk. Unfortunately, they require me to type my long password every time I plug the disk, which is several times per day.

My special need: I don't want to enter a password each time I connect the disk

After initial setup, I would use it this way:

1. Plug the disk to my Linux via USB.
2. Linux somehow recognizes the disk, gets some key stored in my Linux home, use it to mount the disk. Within a few seconds, without asking me for anything.
3. I can use the disk normally.

I am on Ubuntu, if that matters. Bonus if the password can be saved to a file, so that my disk content does not become unreadable forever if my PC is stolen.

Answer 1

You can use LUKS encryption for your external hard drive.

Anytime you plug in the drive, Ubuntu automonts the drive and directly asks for the password. Showing you an option when to forget it:

• immediately
• at the end of the session
• never

--> looks like this:

^{Unlock dialog (source: gnu-designs.com; click image to enlarge)}

Answer 2

You could use TrueCrypt. This has a "cache passwords in memory" option, that will do this for you.

This is a cross-platform solution, so you can also easily then mount the drive on Windows, etc.

If you use the pre-boot authentication to encrypt your system drive, then you can even cache that password, so you never have to enter the password for external drives.

[Yes, I know Truecrypt is out of support, but it still works well enough for most purposes]