Friday, September 16, 2011

Linux udev: two-factor USB token turned into a car ignition key

We use two-factor authentication at work. The one-time token generator looks a lot like an automobile key. It is easy to modify Linux to make a silly car noise when the token generator is plugged in. It turns your lame one-time token into a cool ignition key for your laptop.

Here is a video that shows what it looks like:

To do this for your device, create a shell script to make the sound of a car. I have created an audio file called car.mp3 containing the car sound. The shell script plays this file with mplayer. Record the sound of your car, or grab a file from the internet.
$ cat /root/
# Play a silly car starting sound
mplayer /root/car.mp3 &
Now you need obtain the vendor ID. Disconnect your token generator and run this command:
$ udevadm monitor
Now insert your device. You will see an output like this:
KERNEL[] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1 (usb)
KERNEL[] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0 (usb)
KERNEL[] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/0003:1050:0010.0015 (hid)
UDEV  [] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1 (usb)
UDEV  [] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0 (usb)
UDEV  [] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/0003:1050:0010.0015 (hid)
KERNEL[] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/input/input33 (input)
UDEV  [] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/0003:1050:0010.0015/hidraw/hidraw0 (hidraw)
KERNEL[] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/input/input33/event13 (input)
KERNEL[] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/0003:1050:0010.0015/hidraw/hidraw0 (hidraw)
UDEV  [] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/input/input33 (input)
UDEV  [] add  /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1:1.0/input/input33/event13 (input)
The part after the 0003: is your vendor ID. Of course, it will be different for you. Now create a udev rule to specify the action. This is what my rule looks like:
$ cat /etc/udev/rules.d/90-token.rules
# Make a silly sound like the starting of a car
SUBSYSTEM=="usb", ATTR{idVendor}=="1050", MODE="0664", GROUP="plugdev", RUN+="/root/"
That's it, you don't need to restart anything. If you have done it correctly, then the car sound will play every time you insert your key.