You arrive at work and find a USB flash drive on your desk; it’s not yours but would you plug it in? Over the years you’ve heard a plethora of security-related reasons not to plug in random USB drives, yet as penetration testers know, curious people who know better still plug in a USB drive found in a parking lot. The scenario about finding a drive on your desk at work is one asked by an engineer who developed a USB drive that could turn your laptop or desktop into toast.
An engineer going by the alias of “Dark Purple” was allegedly inspired to build USB killer, what is basically a USB bomb, after reading about a guy who plugged in a USB and “burnt half” of his laptop down. Within a week, Dark Purple came up with a plan and ordered the components. While testing the prototype, Dark Purple “burnt down everything I could. Then I developed and ordered printed circuit boards in China and made a combat model.”
USB killer was described by the engineer’s “former colleague” as being “like an atomic bomb: cool to have, but cannot be applied.” The end product appears relatively boring and “harmless.”
USB ports can provide power, such as when you charge your phone or other device via USB. The USB killer at first acts like a normal storage USB while it pulls and stores power until it reaches negative 110 volts; then it sends that surge back into the system. Zap! Not only will that power returned sizzle components and overload circuits, but it will also damage processors. Both AMD and Intel have USB controllers in their CPU die, or core of the computer chip.
Thankfully Dark Purple decided against posting step-by-step directions, full schematics and all the app details; however there are a couple of shots showing the soldering.
The basic idea of the USB drive is quite simple. When we connect it up to the USB port, an inverting DC/DC converter runs and charges capacitors to -110V. When the voltage is reached, the DC/DC is switched off. At the same time, the filed transistor opens. It is used to apply the -110V to signal lines of the USB interface. When the voltage on capacitors increases to -7V, the transistor closes and the DC/DC starts. The loop runs till everything possible is broken down. Those familiar with the electronics have already guessed why we use negative voltage here. I'll explain to others that negative voltage is easier to commutate, as we need the N-channel field resistor, which, unlike the P-channel one, can have larger current for the same dimensions.
Some folks might consider USB killer to be a prank, but “prank” implies it might be funny to some people; only an enemy would consider physical sabotage to be funny. Nevertheless, some commenters on Kukuruku want the full schematics to brick devices and some others want to buy USB killer.
The next time you find a USB stick and are curious to know its content, hopefully you’ll stop and remember USB killer.