How to Geek has an excellent article about encrypting your Ubuntu home directory
read it here: link
Ubuntu offers to encrypt your home folder during installation. If you decline the encryption and change your mind later, you don’t have to reinstall Ubuntu. You can activate the encryption with a few terminal commands.
Ubuntu uses eCryptfs for encryption. When you log in, your home directory is automatically decrypted with your password. While there is a performance penalty to encryption, it can keep private data confidential, particularly on laptops that may be stolen.
Before doing any of this, you should ensure you have a backup of your home directory and important files.
First, install the encryption utilities:
You’ll have to encrypt your home directory while you’re not logged in. This means that you’ll need another user account with administrator (sudo) privileges
Select your other, (temporary) user account on the login screen and log in with it.
Run the following command to encrypt your home directory, replacing user with the name of your user account:
You’ll have to provide your user account’s password. After you do, your home directory will be encrypted and you’ll be presented with some important notes. In summary, the notes say:
Log out and log back in as your original user account. Do not reboot your system before logging back in!
After you log in, click the Run this action now button to create a recovery passphrase. Keep this passphrase somewhere safe – you’ll need it if you have to manually recover your files in the future.
You can run the ecryptfs-unwrap-passphrase command to view this passphrase at any time.
When you set up an encrypted home directory while installing Ubuntu, your swap partition is also encrypted. After setting up home directory encryption, you’ll also want to set up swap encryption. To do so, run the following command in a terminal:
Note that an encrypted swap won’t work properly with Ubuntu’s hibernate feature – which is disabled by default, anyway.
After restarting your system once or twice and verifying everything works properly, you can clean everything up. You can remove the backup home folder located in your system’s /home directory. Run Nautilus as gksu nautilus to do so.