Jul 1, 2007

How To Fully Encrypt Your Ubuntu Installation

I found this little "how-to" guide on doing a full hard drive encryption of Ubuntu. Fully encrypting your operating system can prevent people from getting access to your files using some form of live CD or other methods. I previously blogged about full hard drive encryption here, but that was mainly for Windows (some forms of Linux were supported, but not Debian based distros like Ubuntu).

Anyway, these instructions were written by Rudá Moura, on the Ubuntu Forums, and was originally performed on Ubuntu 5.10, but most principles should still work on the latest version.

I would also like to mention that Rudá gives instructions for using the text editor vi, which can be kind of hard to use for beginners. If you are a Windows convert and are used to using notepad, then use gedit instead when operating in the GUI. I prefer nano or pico myself from the terminal which is what you will be in when you do this, but that is neither here nor there. Anyway, without further ado, here are the instructions:

Part 1: Ubuntu installation

Install Ubuntu with server profile with the following initial partitioning scheme:

/dev/hda1 /boot 100 MB ext3
/dev/hda2 / 512 MB ext3

Mark that 512 MB is really the shortest size you can set for a server type of installation. A complete Ubuntu installation requires at least 2.4 GB. Make your choice now. In addition, I created two more spaces to hold my future encrypted root and /home partitions, so as the following:

/dev/hda3 future / 10GB
/dev/hda4 future /home 30GB

Set these partitions in the installer option for filesystem as "do not use the partition". Note that it is not absolutely necessary to have an exclusive /home partition, so this is optional since you can have only one partition for a whole encrypted system. Just ignores the alert about not having a swap partition and keep walking.

Part 2: Cryptography software installation

Configures your apt to use all the optional repositories which come with Ubuntu. This is done by modifying /etc/apt/sources.list, uncommenting all the “deb” repositories. Since you are on a terminal with no gedit or something like that, you will need a pure text editor such as Vi. If you know how to use it, don't care for the following explanation for begginers: to edit text files on a terminal using the Vi command, follow this example:

# vi /etc/apt/sources.list

Press “i” to enter in the INSERT mode, make the alterations, press ESC to enter the COMMAND mode and then press SHIFT+zz (ZZ) to save and quit.

Just install the following additional packages: crypsetup 1.0.1, hashalot 0.3, initrd-tools 1.78 e cramfsprogs 1.1 with the command:

# apt-get install cryptsetup hashalot initrd-tools cramfsprogs

Important: initrd-tools must be updated to 1.78 version, because the original one that comes with Ubuntu has a severe bug which makes it unusable.

Part 3: Creating the encrypted system

Now it is time to create the cryptography devices. First, root: choose a trustworthy password, so that you will not end with a weak security implementation. Do not even use your personal login password. Observe that it is hard to change this password later (you would need to re-encrypt the full system again) and this is not explained in this article. The password for /home can be more weak, because it will be stored encrypted inside the file /etc/keys/home (remember that / is being fully encrypted). This is necessary to avoid that /home password would be asked at every boot in order to be mounted.

# cryptsetup -y create root /dev/hda3
# sha256 > /etc/keys/home
# cryptsetup -d /etc/keys/home create home /dev/hda4

The password for root will be asked twice, but the one for /home will be asked only one time and it does not provide confirmation! The partitions with support for cryptography will be available at /dev/mapper/. Now create the filesystem. I prefer the XFS filesystem (this is the one for high performance boxes created by Silicom Graphics, with no undelete policies and 64bit technology. Also there are not tools for windows which can be used to mount a xfs system – but who cares since now we are going to be encrypted!) You can use any filesystem supported by Ubuntu and the one everyone use is ext3, but that's a matter of taste.

# mkfs -t xfs /dev/mapper/root
# mkfs -t xfs /dev/mapper/home

Now mount the new partitions to /mnt and copy the old root to the new one at /mnt. This will be a perfect copy, preserving data, symbolic links and everything.

# mount /dev/mapper/root /mnt
# mkdir /mnt/home
# mount /dev/mapper/home /mnt/home
# cp -axv / /mnt

The copy process took two minutes and a half for a server profile and sixteen for a complete installation. Mount /dev inside /mnt/dev to get access to the devices.

# mount --bind /dev /mnt/dev

Part 4: Adjusts inside chroot

Enter the encrypted system by using the chroot command and mount /boot, /proc and /sys:

# chroot /mnt
# mount /boot
# mount /proc
# mount /sys

This step must be done in order to fix a bug in Ubuntu, but do not ask me why..

# ln -sf /lib/libdevmapper.so.1.01 /lib/libdevmapper.so.1.00

Edit /etc/crypttab and add the following lines:

root /dev/hda3
home /dev/hda4 /etc/keys/home

Edit /etc/fstab in order to change root to the new mounting point at /dev/mapper/root and add a line for /home. I did it this way:

/dev/mapper/root / xfs defaults 0 1
/dev/mapper/home /home xfs defaults 0 2

Edit /etc/kernel-img.conf and add the following line:

ramdisk = /usr/sbin/mkinitrd

Edit /boot/grub/menu.lst, search for kopt and change this line to:

# kopt=root=/dev/mapper/root devfs=mount ro

Note that the initial # should NOT be removed!

Asks it to reconfigure kernel so that it obtains a new file for grub and a new initrd image able to support cryptography.

# dpkg-reconfigure linux-image-2.6.12-9-386

This command takes into consideration that the installed kernel is the original one from the installation, but if it is NOT the case, substitute it properly – for example, 686 instead of 386, or any other updated version.

Part 5: Finishing

Unmount all chroot file systems, quit chroot and reboot:

# umount -a
# exit
# reboot

If everything worked fine, your system will ask for the password in order to mount /root and then the boot process will continue. If you type a wrong password the system will not output any alert and will fail drastically, probably with a Kernel Panic.

Part 6: Encrypted Swap

This process is like the other we done for /home, but the only difference is that the password will be different for every boot, since it will be read from /dev/random.

# cryptsetup create swap /dev/hda2

Type any **** as password, since it will not be used by the user.

Edit /etc/crypttab and add the line for swap:

swap /dev/hda2 /dev/random swap

Edit /etc/fstab and add the file for swap:

/dev/mapper/swap none swap sw 0 0

To enable swap immediately:

# cryptsetup remove swap
# /etc/init.d/cryptdisks start
# swapon -a

From this moment your whole filesystem is encrypted. In order to turn your server instalation into a default and complete one, just do it:

# apt-get install ubuntu-desktop

Don't Forget your Bauer-Power Gear!

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