Tails above the Rest: the Installation
A few columns ago, I started a series aimed at helping everyone improve their privacy and security on the Internet. The first column in this series was an updated version of a Tor column I wrote a few years ago. While the new column talked about how to get up and running with Tor using the Tor Browser Bundle, in my original Tor column, I talked about how to browse even more anonymously by using a Knoppix live CD and live-installing Tor on top of it. That way, when you were done with your session, you simply could reboot and remove the Knoppix disc, and the host computer would be back to normal with no trace of your steps. Although the Tor Browser Bundle is incredibly useful, it doesn't cover the case where you would like to use Tor on a computer you don't own, much less using Tor without leaving a trace.
These days, there is a much better option than a Knoppix live CD—a live DVD/USB distribution called Tails, which does so much more than provide a live CD with Tor installed. Think of it like a live DVD version of the Tor Browser Bundle, only for the entire OS. With Tails, you boot in to a live environment either from a DVD or USB stick that is set with incredibly secure defaults. Tails takes great lengths to provide you with a secure, anonymous environment. Among other things, Tor automatically launches and connects once you start the desktop, and all communications are routed over it. By default, nothing you do in your desktop session persists—everything is not only erased when you reboot, Tails actually goes further and attempts to scrub the contents of RAM before it does reboot. Tails includes a Web browser configured much like in the Tor Browser Bundle with a number of privacy-enhancing plugins and settings already in place. Beyond that, it includes a password manager (Keepassx), GPG encryption software, an e-mail program (Claws), LUKS disk encryption software, secure chat via Pidgin with the OTR (Off the Record) plugin already installed, and it even includes an on-screen keyboard you can use to type in passwords if you are concerned a keylogger might be installed on your host machine.
In the next few columns, I'm going to discuss how to get and validate the Tails distribution and install it. I will follow up with what Tails can and can't do to protect your privacy, and how to use Tails in a way that minimizes your risk. Then I will finish with some more advanced features of Tails, including the use of a persistent volume (with this feature, depending on your needs, you could conceivably use Tails as your main Linux distribution).
If there is someone you trust who already has Tails, installation is easy. Either have them make a copy of their DVD, or in the case of a USB install, have them boot a computer into Tails, insert your USB disk, and then click Applications→Tails→Tails Installer. Finally, click Clone & Install in the GUI window that appears, and Tails will wipe out any data on your USB disk and clone itself there.
If you don't already know someone with Tails, installing Tails is a little bit more involved than with a normal live DVD. This is because if you truly want to use Tails for its intended purpose—security and anonymity—you will want to perform a few additional steps to confirm that the version of Tails you downloaded hasn't been tampered with.
If you have read my column about the Tor Browser Bundle, these steps will seem familiar. In addition to downloading the ISO image, instead of downloading an md5sum to validate it, you also will download a cryptographic signature. Then you will use that signature to validate that ISO image is the legitimate unmodified version. Finally, if you burn to a DVD, you will follow the same procedure you would use for any other DVD image, or if you want to install to a USB disk, there are a couple extra steps. I'll go over all of this below.
First, let's get Tails. The official Tails site is at https://tails.boum.org. (It's HTTPS, so be sure to check whether you get a certificate warning.) From the main page, you should see an image you can click to take you to the download page for the latest version of Tails (at the time of this writing, the latest version is 0.22). At the download page, you should see two main options: either download the ISO image and the corresponding signature as separate downloads, or use the torrent download, which will pull both files down together. The ISO is almost 1GB, so depending on your Internet connection, it may take some time. Once you have both the .iso file and the corresponding .sig signature file, you are ready to move on to validating the image.
Validate the ISO Image
Normally when you download an ISO or other large file, there is a .md5 checksum file that corresponds to it. The purpose of the .md5 file is just to validate that the large ISO file wasn't corrupted during the download and that the file that is on your desktop matched the file on the server. In the case of security software like Tails, unfortunately that kind of verification isn't enough. In particular, if attackers were able to position themselves between you and the Tails server (a Man in the Middle or MITM attack), the attackers potentially could send you a modified version of the Tails ISO that contained a backdoor. If they could do that, they also could send you a matching .md5 checksum file that matches their ISO.
To counter this threat, instead of a .md5 checksum, Tails has you download a cryptographic signature file created by the private key of the Tails maintainer. Much like cryptographic checksums on your distribution's packages, this signature file could be created only by a person with access to a specific GPG private key. In a MITM attack scenario, if attackers try to send you a modified version of the ISO, they would not be able to send you a modified version of the .sig signature file that would match without themselves having access to the official private key.
Kyle Rankin is a director of engineering operations in the San Francisco Bay Area, the author of a number of books including DevOps Troubleshooting and The Official Ubuntu Server Book, and is a columnist for Linux Journal.