Hack: How to spy on a 3-D printer

Smartphones can figure out what a printer makes by analyzing the noise and energy it emits
Nov 18, 2016 — 7:00 am EST
3-D printer spy

A thief with bad intentions might use a smartphone to spy on a 3-D printer. That phone would listen for the sounds (acoustic waves) and electromagnetic energy emitted by a printer while it’s working.

Wenyao Xu

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

Your 3-D printer is leaking, but not in ways you can see. It leaks sounds and energy. That's not a problem — unless you want to keep your creation a secret. In that case, it's time to get serious about security. Computer scientists have now shown that hackers can eavesdrop on 3-D printers — and then copy what they made. All it takes is your average smartphone.

As 3-D printing becomes more widespread, thieves will find new ways to steal original designs, worries Wenyao Xu. This computer scientist at the State University of New York in Buffalo led the new work. Right now, 3-D printing technology is still in the early stages. But before long, it could be used to print anything from spare parts for appliances to human organs. Large printers already have been used to print an entire house. Manufacturers could use such printers to create parts for airplanes. And it is creations like this where security becomes an issue. A hacker who steals a wing design might be able to change it — and sabotage the plane, for example.

“We need to prevent these attacks,” Xu says.

This kind of printing is also known as additive manufacturing. Its use has been skyrocketing in recent years as costs for the hardware and printing “ink” have dropped.

An ordinary computer printer creates a flat version of a document by putting ink on paper. A 3-D printer works in a similar way. Most 3-D printed objects lay down one thin layer at a time. Its “ink” is what really distinguishes it. The printer’s nozzle deposits a thin layer of liquid plastic or metal, which solidifies or hardens as it cools. By building up layer after layer of the ink, the machine creates a solid, three-dimensional object.

To hack these printers, a spy needs to merely “listen” to the noise and energy the machine emits, including the magnetic fields that vary as it works. Both sound and electromagnetic energy travel as waves. By tapping into these waves, Xu says, a spy could identify the shape of what was being printed. This would allow someone to steal a design without ever seeing the original.

The human ear isn’t sensitive enough to do this. So Xu used a smartphone. Today’s average smartphone contains powerful microphones and other sensors. They can record the sound and changing magnetic fields produced as a 3-D printer works, Xu’s team showed.

The scientists used a two-step process to turn a smartphone into a spying device. First came the training phase. During this step, they used the phone to collect data as a printer printed. At the same time, they noted the up-and-down and side-to-side movements of the nozzle. By comparing the two sets of data, they could match changes in the sound or magnetic fields that reflected the movement of the nozzle. The scientists built these connections into a computer program.

Then came the testing. Using what they'd learned in the first step, the researchers had their computer program analyze data as something different was printed. A smartphone had recorded the sounds and magnetic fields during the process. The “trained” program successfully translated the new data into nozzle movements. And they revealed what had been printed.

Their inspiration

This type of data theft is known as a “side-channel attack.” It steals information by spying on a machine, rather than by swiping an object or hacking the computer program used to make it. Side-channel attacks in the new tests spied on a printer’s sounds and magnetic energy.

3-D printed keys
Scientists used smartphones to eavesdrop on a 3D printer. Based on their spying, they were able to create a copy (lower) of the original printed object (above). In their test, the object was a key.
Wenyao Xu

Xu’s group used data stolen from a working printer by their phone to copy an abstract but complex shape. It looked like a key. And the copy proved nearly identical to the original. Currently, this side-channel data can be used to print an object with 90 percent accuracy, Xu’s team showed.

Xu says this hack was inspired by the sounds he hears around him. People learn a lot by listening. “If we hear someone eating chips, we know they're eating chips,” says Xu. “If someone is drinking water, we know they're drinking.” So it goes with printing. His group suspected they could tell a lot about what a 3-D printer in the lab was printing, simply by listening to it. Then they set about testing that suspicion.

The group presented their results at a scientific conference in Vienna, Austria, on October 26.

Others have been concerned

Xu isn't the first scientist to probe side-channel attacks on 3-D printers. Scientists at the University of California, Irvine, published an April 2016 analysis of acoustic (sound-based) side-channel attacks. Computer scientist Mohammad Al Faruque led those studies. His team has now identified several ways someone could eavesdrop on a 3-D printer, he says. Besides sound and magnetic fields, a spy could use data on heat or vibrations or power. The more sensors a spy uses, the more accurate their stolen data will be — and the more valuable the theft, Al Faruque points out.

Al Faruque says he's glad researchers like Xu are expanding on his original work. “I'm happy that we discovered it and that people have started doing more research,” he says. “It is very important.”

Both Xu and Al Faruque say they're now working on ways to beef up the security for 3-D printers. A printer might be shielded to avoid leakage, for example. Or extra noise might be added to the environment to confuse any listening “ear.” Ultimately, both researchers have the same goal.

“We don't want to steal ideas,” says Xu. “We want to protect them.”

Power Words

(for more about Power Words, click here)

acoustics      The science of sounds and hearing.

3-D printing     A means of producing physical items — including toys, foods and even body parts — using a machine that takes instructions from a computer program. That program tells the machine how and where to lay down successive layers of some raw material (the “ink”) to create a three-dimensional object.

abstract     Something that exists as an idea or thought but not concrete or tangible (touchable) in the real world. Beauty, love and memory are abstractions; cars, trees and water are concrete and tangible.

additive manufacturing     This process of creating solid objects by depositing material, micro-layer by micro-layer (or slice by slice) from the bottom up. It’s an explanation for how 3-D printing works.

computer program     A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

data     Facts and/or statistics collected together for analysis but not necessarily organized in a way that give them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.

electromagnetic radiation      Energy that travels as a wave, including forms of light. Electromagnetic radiation is typically classified by its wavelength. The spectrum of electromagnetic radiation ranges from radio waves to gamma rays. It also includes microwaves and visible light.

field      (in physics) A region in space where certain physical effects operate, such as magnetism (created by a magnetic field), gravity (by a gravitational field) or mass (by a Higgs field).

hack       (in computing) To get unapproved — often illegal — access to a computer, usually to steal or alter data or files.

magnetic field     An area of influence created by certain materials, called magnets, or by the movement of electric charges.

manufacturing     The making of things, usually on a large scale.

nozzle     A round spout or slot at the end of a pipe, hose or tube. Nozzles are typically used to control the flow of a jet of high-pressure liquid or gas.

sensor     A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.

side channel attack      (in computing) To acquire indirect information (such as heat, sound, radiation) from a system as a form of spying. Later, these data may be analyzed collectively to piece together the function of the system from which they were acquired.

smartphone     A cell (or mobile) phone that can perform a host of functions, including search for information on the Internet.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.


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Meeting: W. Yu et al. My smartphone knows what you print: Exploring smartphone-based side-channel attacks against 3D printers. 23rd ACM Conference on Computer and Communications Security. October 2016. Vienna, Austria. doi: 10.1145/2976749.2978300.

Meeting: M.A. Al Faruque et al. Acoustic side-channel attacks on additive manufacturing systems. 2016 ACM/IEEE 7th International Conference on Cyber-Physical Systems (ICCPS), April 11-14, 2016. Vienna, Austria. doi: 10.1109/ICCPS.2016.7479068.