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BackTrack 3, the EEE 701, and Disk Encryption

Explanation and Advantages

I recently decided to make BackTrack 3 the primary OS on my pearly EEE 701.  Given my EEE’s whopping 4GB of solid-state storage, I decided that rather than installing BackTrack directly onto the SSD, I would instead install the live distro to an 8GB SDHC card I had lying around, and use the remaining internal 4GB SSD as an encrypted /root partition using cryptsetup.  There are a few distinct advantages of such a setup.  Firstly, since the OS is installed as a live distro on a removable device, portability is not sacrificed – I am still able to boot into BackTrack from the same SDHC card plugged into another machine (assuming, of course, that machines BIOS supports booting from SD.)  Secondly, by overriding the default /root partition which is created by root.lzm, any changes I make to /root are persistent, and do not require a recompression of root.lzm.  This allows me to store application settings and files in a much more convenient manner.  Thirdly, since /root is encrypted, saving settings or files containing passwords or other sensitive information is less of a security risk.


To install BackTrack onto the SDHC card, we use the same method as a USB install.  Format the SDHC to contain a vfat filesystem.  Extract the BackTrack 3 USB .iso file into the filesystem mount point, and run boot/bootinst.sh.  I tried this in Ubuntu 8.10, and had some trouble: the device was recognized as /dev/mmcblk0 and the partition as /dev/mmcblk0p1, a designation that shell script got mixed up on.  Running the script on the EEE’s previous OS, Xubuntu 8.04, the device and partition were recognized as /dev/sda and /dev/sda1, and I encountered no further problems.

Once we boot into BackTrack, we configure and install cryptsetup:

cd ~
wget http://luks.endorphin.org/source/cryptsetup-1.0.5.tar.bz2
tar -xvf cryptsetup-1.0.5.tar.bz2
cd cryptsetup-1.0.5
make install

Next, we create a .lzm file for cryptsetup to ensure that it will be available each time we boot:

mkdir -p usr/include usr/lib usr/man/man8 usr/sbin usr/share/locale/de/LC_MESSAGES
cp /usr/include/libcryptsetup.h usr/include/
cp /usr/lib/cryptsetup usr/lib/
cp /usr/lib/libcryptsetup.* usr/lib/
cp /usr/man/man8/cryptsetup.8 usr/man/man8/
cp /usr/sbin/cryptsetup usr/sbin/
cp /usr/share/locale/de/LC_MESSAGES/cryptsetup.mo usr/share/locale/de/LC_MESSAGES/
tar -zcvf cryptsetup.tgz usr/
tgz2lzm cryptsetup.tgz cryptsetup.lzm
cp cryptsetup.lzm /mnt/sda1/BT3/modules/ # my mountpoint was /mnt/sda1, yours probably is too

Now we have cryptsetup available in the live environment.  Next step is to format the EEE’s internal SSD.  I set up one primary filesystem, recognized as hdc1.  We’ll be formatting this with cryptsetup using a secure passphrase.

cfdisk # to set up the partition
umount /dev/hdc1
cryptsetup luksFormat /dev/hdc1
cryptsetup luksOpen /dev/hdc1 root_dir
mkfs.ext2 /dev/mapper/root_dir

And now we have an encrypted partition on the SSD.  Next mount it and copy the existing BackTrack /root files.

mkdir /mnt/root_dir
mount /dev/mapper/root_dir /mnt/root_dir
cp -a /root /mnt/root_dir
mv /mnt/root_dir/root/* /mnt/root_dir/root/.* /mnt/root_dir/
rmdir /mnt/root_dir/root

And we’re almost done.  We’ll create a script to make it easy to mount our /root every time we boot.  Create a file in /root/root/decrypt_root.sh with the following contents:

cryptsetup luksOpen /dev/hdc1 root_dir
mount /dev/mapper/root_dir /root

Finally, create an .lzm file for the script.

cd ~
tar -zcvf decrypt_root.tgz root/
tgz2lzm decrpyt_root.tgz decrypt_root.lzm
cp decrypt_root.lzm /mnt/sda1/BT3/modules/

And we’re finished.  If all goes well, when you restart your machine you will have this script in your /root directory, and once run it will mount your encrypted SSD partition to /root.  From this point, you can issue a ctrl-alt-backspace and re-login, and startx if you’d like.  Welcome to a world of BackTrack possibilities!

Cory Doctorow’s Little Brother

I just finished Cory Doctorow‘s Little Brother. And oh. My. God. Soooo good. Sooooooo good.

First let me note: Cory Doctorow is a sci-fi author, but this novel doesn’t read like sci-fi. Sure, it hinges on technology that doesn’t yet exist. But we’re talking about the near future, the very near future, no more than 4-5 years down the line. So there’s no robots with plasma spheres for heads screaming “Danger Will Robinson!,” or faster than light travel, or any of those elements that have given the genre an unfair reputation. Instead, it’s tech that we can see developing before our very eyes in real-time. In every chapter there is an explanation of real or conceivable computer systems, cryptographic systems, or mathematics that are relevant to the story in some way. And that’s the exciting part: the innovativeness and imagination that is embodied in the not-so-far-off world that Doctorow describes is believable because it comes from the authors understanding of how the technology really works, and how it is evolving in the present. As William Gibson explains, sci-fi “can’t be about the future. It’s about where the person who wrote it thought their present was, because you can’t envision a future without having some sort of conviction, whether you express it or not in the text, about where your present is.” And our present is a very exciting time indeed.

That being said, even without an understanding of the underlieing technology, it makes for a great read. Basically, it’s about a teenage hacker in San Francisco and how he deals with the Department of Homeland Security (DHS) taking over the bay area after the next terrorist attack. The DHS sets up random checkpoints throughout the city, extending the surveillance measures already in place, and tracks the movements of every citizen through the RFID tags they use when they take the BART (subway), or go through the FastTrac (RFID-enabled toll booth lane in SF). Furthermore, our protagonist and his friends are taken in and tortured by the DHS for days on end, in a secret prison the department has set up offshore. With this imagery, you can see how Doctorow’s vision of the near-future is also informed by the political realities of our time. Just as he projects the technologies of the near future based on the technological dynamics of the present, the stark political realities of today are extended into the near future in a way that seems not just believable, but inevitable. I’m not going to give away too much of the plot, but here’s the long and short of it. Just as these technologies can be used against the people, those same technologies can be used to promote and extend peoples rights and freedoms, and to subvert the governments attempt to take those freedoms away. A movement evolves, and at the center of it is the Xnet – an encrypted network of hacked Xbox Universals, using Paranoid Linux as its operating system.

Doctorow does such a wonderful job of interweaving the political, cultural, and technological strains of our current society and projecting them into the near future with an elegance that it is truly visionary. Anyone who is interested in cryptography, hacking, or activism should immediately drop whatever they’re doing, run to their nearest independent bookstore, and pick up a copy of this immediately. Well? Go!