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Wednesday, August 16, 2017

Securing 3D printers with gold nanorods

By Nick Flaherty

Researchers from the Georgia Institute of Technology and Rutgers University have developed a three-layer system to verify that components produced with 3D printing have not been compromised. 

The system uses acoustic and other physical techniques to confirm that the printer is operating as expected, and nondestructive inspection techniques to verify the correct location of tiny gold nanorods buried in the parts. The key is that the technique is independent of printer firmware and software in the controlling computer which may itself have been compromised.

"These 3-D printed components will be going into people, aircraft and critical infrastructure systems," said Raheem Beyah, the Motorola Foundation Professor and associate chair in Georgia Tech's School of Electrical and Computer Engineering. "Malicious software installed in the printer or control computer could compromise the production process. We need to make sure that these components are produced to specification and not affected by malicious actors or unscrupulous producers."

The technique uses acoustic measurement of the 3-D printer in operation. When compared to a reference recording of a correct print, this acoustic monitoring -- done with an inexpensive microphone and filtering software -- can detect changes in the printer's sound that may indicate installation of malicious software.

It also uses physical tracking of printer components. To create the desired object, the printer's extruder and other components should follow a consistent mechanical path that can be observed with inexpensive sensors. Variations from the expected path could indicate an attack.

The detection of the nanorods in the finished components is the third element. This uses Raman Spectroscopy and computed tomography (CT) to detect the location of gold nanorods that had been mixed with the filament material used in the 3-D printer. Variations from the expected location of those particles could indicate a quality problem with the component. The variations could result from malicious activity, or from efforts to conserve printer materials. This uses similar techniques to medical imaging, and the gold contrast materials were tested to make sure they wouldn't compromise the structural integrity of the printed components.

The researchers tested their technique on three different types of 3- printers and a computer numerical control (CNC) machine using a polyethylene tibial knee prosthesis as a test case. Beyond detecting malicious activity or quality problems, the technique could stop inadvertent production problems, reducing materials waste.

"Our focus now will be on testing the resilience of this technology and its resistance to intrusion and malicious attacks," said Javanmard.

Among the challenges ahead will be obtaining good acoustic data in the noisy environments in which 3-D printers typically operate. In the research reported by the researchers, operation of other 3-D printers near the one being observed cut the accuracy significantly, but Beyah believes that challenge can be addressed with additional signal processing. The technique will also be applied to additional types of printers, and to different materials.

With the capabilities of 3-D printers growing and their cost declining, Beyah believes the use of additive manufacturing techniques will continue to expand. The validation and intrusion detection system will therefore become more critical.

"The idea that additive manufacturing processes could be compromised to intentionally hurt someone hasn't really been considered with some of these applications," he said. "There is a good bit of room to improve the security of 3-D printers, and we think that will start with applications that are closest to humans, such as implants and medical devices."

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