Tinfoil Hat Linux (THL) was a compact Linux distribution designed for high security. Version 1.000 was released in February 2002. It appears to be no longer actively maintained as of 2006, though the files are still available in gzip format. THL requires a 386DX computer or better, with at least 8 MB of RAM. The distribution fits on a single ordinary HD floppy. The small footprint provides additional benefits beyond making the system easy to understand and verify- the computer need not even have a hard drive, making it easier to "sanitize" the computer after use. Many of these concepts have been carried over into larger and more modern Live CD distributions such as Knoppix.
The logo of Tinfoil Hat is Tux, the Linux mascot, wearing a tinfoil hat.
Tinfoil Hat uses a number of sophisticated measures to defeat hardware and software surveillance methods like keystroke logging
, video camera
, and TEMPEST
- Encryption — GNU Privacy Guard (GPG) public key cryptography software is included in THL.
- Data retrieval — All temporary files are created on an encrypted ramdisk that is destroyed on shutdown. Even the GPG keyfile information can be stored encrypted on the floppy.
- Keystroke monitoring — THL has gpggrid, a wrapper for GPG that lets you use a video game style character entry system instead of typing in your passphrase. Keystroke loggers get a set of grid points, not your passphrase.
- Power usage and other side channel attacks — Under the Paranoid options, a copy of GPG runs in the background generating keys and encrypting random documents. This makes it harder to determine when real encryption is taking place.
- Even reading the screen over the user's shoulder is very hard when Tinfoil Hat is switched to paranoid mode, which sets the screen to a very low contrast.
An advantage of THL is that it can be used on virtually any modern PC
using the x86
processor architecture. For example, one might install it on a computer that is kept in a locked room, not connected to any network
, and used only for cryptographically
. While the paranoid
mode security measures may seem over the top and might be found funny, they are a good education in the types of issues that must be considered for high security. It is fairly easy to create the Tinfoil Hat booting
floppy with Microsoft Windows
. Verifying the checksum
can be more tricky. The text of the documentation is salted with just a few jokes, which reinforces their humor by the stark contrast with the serious and paranoiac tone of the surrounding text- the very name pokes fun at itself, as Tinfoil hats
are commonly ascribed to paranoiacs as a method of protecting oneself from mind-control waves.
Tinfoil Hat Linux requires one to work in a text-only environment in Linux, i.e. starting straight off with a Bourne shell and the editor vi, not a graphical user interface. It uses BusyBox instead of the normal util-linux, the GNU coreutils (formerly known as fileutils, shellutils and textutils) and other common Unix tools. While vi can be arcane, Tinfoil Hat also offers the simpler nano text editor.