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Implementing LUKS encryption on your Linux laptop
In my last blog post [Full Disk Encryption for Your Laptop] explained my decisions relating to Full-Disk Encryption (FDE) for my laptop. Wrapping up my week's theme of Full-Disk Encryption, I thought I would explain the steps involved to make it happen.
Last April, I switched from running Windows and Linux dual-boot, to one with Linux running as the primary operating system, and Windows running as a Linux KVM guest. I have Full Disk Encryption (FDE) implemented using Linux Unified Key Setup (LUKS).
Here were the steps involved for encrypting my Thinkpad T410:
Step 0: Backup my System
Long-time readers know how I feel about taking backups. In my blog post [Separating Programs from Data], I emphasized this by calling it "Step 0". I backed up my system three ways:
Backed up all of my documents and home user directory with IBM Tivoli Storage Manager.
Backed up all of my files, including programs, bookmarks and operating settings, to an external disk drive (I used rsync for this). If you have a lot of bookmarks on your browser, there are ways to dump these out to a file to load them back in the later step.
Backed up the entire hard drive using [Clonezilla].
Clonezilla allows me to do a "Bare Machine Recovery" of my laptop back to its original dual-boot state in less than an hour, in case I need to start all over again.
Step 1: Re-Partition the Drive
"Full Disk Encryption" is a slight misnomer. For external drives, like the Maxtor BlackArmor from Seagate (Thank you Allen!), there is a small unencrypted portion that contains the encryption/decryption software to access the rest of the drive. Internal boot drives for laptops work the same way. I created two partitions:
A small unencrypted partition (2 GB) to hold the Master Boot Record [MBR], Grand Unified Bootlloader [GRUB], and the /boot directory. Even though there is no sensitive information on this partition, it is still protected the "old way" with the hard-drive password in the BIOS.
The rest of the drive (318GB) will be one big encrypted Logical Volume Manager [LVM] container, often referred to as a "Physical Volume" in LVM terminology.
Having one big encrypted partition means I only have to enter my ridiculously-long encryption password once during boot-up.
Step 2: Create Logical Volumes in the LVM container
I create three logical volumes on the encrypted physical container: swap, slash (/) directory, and home (/home). Some might question the logic behind putting swap space on an encrypted container. In theory, swap could contain sensitive information after a system [hybernation]. I separated /home from slash(/) so that in the event I completely fill up my home directory, I can still boot up my system.
Step 3: Install Linux
Ideally, I would have lifted my Linux partition "as is" for the primary OS, and a Physical-to-Virtual [P2V] conversion of my Windows image for the guest VM. Ha! To get the encryption, it was a lot simpler to just install Linux from scratch, so I did that.
Step 4: Install Windows guest KVM image
The folks in our "Open Client for Linux" team made this step super-easy. Select Windows XP or Windows 7, and press the "Install" button. This is a fresh install of the Windows operating system onto a 30GB "raw" image file.
(Note: Since my Thinkpad T410 is Intel-based, I had to turn on the 'Intel (R) Virtualization Technology' option in the BIOS!)
There are only a few programs that I need to run on Windows, so I installed them here in this step.
Step 5: Set up File Sharing between Linux and Windows
In my dual-boot set up, I had a separate "D:" drive that I could access from either Windows or Linux, so that I would only have to store each file once. For this new configuration, all of my files will be in my home directory on Linux, and then shared to the Windows guest via CIFS protocol using [samba].
In theory, I can share any of my Linux directories using this approach, but I decide to only share my home directory. This way, any Windows viruses will not be able to touch my Linux operating system kernels, programs or settings. This makes for a more secure platform.
Step 6: Transfer all of my files back
Here I used the external drive from "Step 0" to bring my data back to my home directory. This was a good time to re-organize my directory folders and do some [Spring cleaning].
Step 7: Re-establish my backup routine
Previously in my dual-boot configuration, I was using the TSM backup/archive client on the Windows partition to backup my C: and D: drives. Occasionally I would tar a few of my Linux directories and storage the tarball on D: so that it got included in the backup process. With my new Linux-based system, I switched over to the Linux version of TSM client. I had to re-work the include/exclude list, as the files are different on Linux than Windows.
One of my problems with the dual-boot configuration was that I had to manually boot up in Windows to do the TSM backup, which was disruptive if I was using Linux. With this new scheme, I am always running Linux, and so can run the TSM client any time, 24x7. I made this even better by automatically scheduling the backup every Monday and Thursday at lunch time.
There is no Linux support for my Maxtor BlackArmor external USB drive, but it is simple enough to LUKS-encrypt any regular external USB drive, and rsync files over. In fact, I have a fully running (and encrypted) version of my Linux system that I can boot directly from a 32GB USB memory stick. It has everyting I need except Windows (the "raw" image file didn't fit.)
I can still use Clonezilla to make a "Bare Machine Recovery" version to restore from. However, with the LVM container encrypted, this renders the compression capability worthless, and so takes a lot longer and consumes over 300GB of space on my external disk drive.
Backing up my Windows guest VM is just a matter of copying the "raw" image file to another file for safe keeping. I do this monthly, and keep two previous generations in case I get hit with viruses or "Patch Tuesday" destroys my working Windows image. Each is 30GB in size, so it was a trade-off between the number of versions and the amount of space on my hard drive. TSM backup puts these onto a system far away, for added protection.
Step 8: Protect your Encryption setup
In addition to backing up your data, there are a few extra things to do for added protection:
Add a second passphrase. The first one is the ridiculously-long one you memorize faithfully to boot the system every morning. The second one is a ridiculously-longer one that you give to your boss or admin assistant in case you get hit by a bus. In the event that your boss or admin assistant leaves the company, you can easily disable this second passprhase without affecting your original.
Backup the crypt-header. This is the small section in front that contains your passphrases, so if it gets corrupted, you would not be able to access the rest of your data. Create a backup image file and store it on an encrypted USB memory stick or external drive.
If you are one of the lucky 70,000 IBM employees switching from Windows to Linux this year, Welcome!