Paranoid Penguin - Customizing Linux Live CDs, Part II

Use encrypted folders with your custom live CD.
Creating an Encrypted Volume

Now, you can create an encrypted volume. For our purposes here, it will be a simple “file vault” to mount as a subdirectory of your home directory. But, it just as easily could be an entire home directory that you mount over the one your live CD uses. Come to think of it, you also could do that with /etc. For now, however, I'll leave it to you to explore the technical subtleties of those usage scenarios (see Resources for some pointers on home directory encryption).

TrueCrypt can be run either in text mode, via the truecrypt -t command (followed by various options) or in graphical mode. For now, let's stick to graphical mode. To start it, simply type the following from within a terminal window:

bash-$ truecrypt &

And, you should see what's shown in Figure 1.

Figure 1. TrueCrypt 5.1 GUI for Linux

Click Create Volume to start the TrueCrypt Volume Creation Wizard. We'll create a standard TrueCrypt volume, not a hidden one (you can hide one TrueCrypt volume inside the “empty” space of another, as all unused space in a TrueCrypt volume is filled with random characters). So, click Next.

In the wizard's next screen, you can specify the path and name of the file in which your encrypted volume will be stored or the name of an entire disk partition to encrypt. Here, we're creating a file-hosted volume, and in our example scenario, this file will be /home/ubuntu/realhome2 (no file extension is necessary). After typing that path, click Next.

In the wizard's third screen, we must specify the volume's size. In this example, I'm creating a 500MB volume.

After clicking Next, you can choose an Encryption Algorithm and a Hash Algorithm. The defaults, AES and RIPEMD-160, respectively, are good choices. You also can click the Test button to make sure TrueCrypt's built-in cryptographic functions work properly on your system.

The next step is to set a volume password. Choose a strong one! You also can specify and create keyfiles—files that TrueCrypt will look for every time you mount this volume. If any keyfile is missing, or if its contents have changed in any way since you created the volume, TrueCrypt won't mount the volume. Properly used, keyfiles can provide another level of authentication to your encrypted volume. But, we aren't going to use any in this example. Enter a password (twice) and click Next.

Important note: TrueCrypt has no back doors of any kind. For this reason, if you forget your volume's password, or if any of its keyfiles are lost or corrupted, you will not be able to recover the contents of your encrypted volume. By all means, choose a difficult-to-guess volume password, but make sure you won't forget or lose it yourself!

Now we come to the Format Options screen, which asks a subtle question: which filesystem? The choices here are FAT, which is actually the Windows 95 vfat filesystem (MS-DOS FAT16 with long filenames), and None. If you select FAT, TrueCrypt will format your new encrypted volume for you. However, vfat isn't a journaling filesystem; it isn't very resilient to file corruption and other filesystem errors.

Worse, strange things can happen if you store certain kinds of Linux system files on a vfat partition, because vfat can't store certain Linux file attributes. The only reason to choose vfat is if you intend to use the volume with both Linux and Windows systems. If you're going to use it only on Linux, especially if you're going to use it as a home directory (or /etc), you should choose None, and formate the virtual partition yourself, which I'll show you how to do in a minute.

For now, click Next to proceed to the Volume Format screen. This is your chance to generate some entropy (randomness) with which TrueCrypt can initialize its crypto engine, pursuant to encrypting your volume. To do so, move your mouse randomly within the window a while, and then click Format.

That's it! You've created /home/ubuntu/realhome2 and now are ready to format it. Click Exit to close the Volume Creation Wizard.

Formatting the Volume

My personal favorite native-Linux journaling filesystem is ext3, so that's what we use here. Before we format our new volume though, we need to have TrueCrypt map it to a virtual device. This isn't really mounting per se, but that's the TrueCrypt function we need to use.

Back in the TrueCrypt GUI (Figure 1), type the full path of our new volume (/home/ubuntu/realhome2) in the text box next to the key icon (or navigate to it using the Select File... dialog), and click Mount. In the box that pops up, enter your volume's password, and then click Options >. Here's where things get a little strange. Click the box next to Do not mount (Figure 2). Now you can click OK.

Figure 2. Not Mounting Our Unformatted Volume

Why, you may wonder, are you telling TrueCrypt “do not mount” in the middle of the Mount dialog? Because, of course, you can't mount an unformatted partition. But, TrueCrypt can map it to a virtual device, and this is, in fact, what TrueCrypt has just done.

Back in the TrueCrypt main screen, your volume file now should be listed in Slot 1. To find the virtual device to which it's been mapped, click Volume Properties. As shown in Figure 3, realhome3 has been mapped to /dev/loop0.

Figure 3. Volume Properties

Now, we can format the new encrypted volume. In your terminal window, type:

05-$ sudo mkfs.ext3 /dev/loop0