3D-Printed Guns and Fingerprints

Law enforcement authorities may soon be able to trace 3D printed guns to the machine it came from. A new study led by University of Buffalo (UB) has discovered a method, called ‘PrinTracker’ that could help forensic investigators trace 3D-printed guns and counterfeit goods to the 3D printer that made them.

3D printing has many uses. However, it’s also a counterfeiter’s dream, worries lead author Wenyao Xu, PhD, associate professor of computer science and engineering in UB’s School of Engineering and Applied Sciences.

“Even more concerning, it has the potential to make firearms more readily available to people who are not allowed to possess them,” Xu said. The study includes coauthors from Rutgers University and Northeastern University.

A Unique Pattern

A 3D printer works like a common inkjet printer i.e. the printer heads move while “printing” an object. And instead of discharging ink, the nozzle discharges a filament in layers, until the desired 3D object is formed.

Each of these layers contains tiny wrinkles, called in-fill patterns. Usually measured in submillimeters, these patterns are supposed to be uniform but are not. In fact, the printer’s model type, nozzle size, and other factors cause slight imperfections in the patterns, which may make the actual object have patterns that vary 5 to 10 percent from the design plan.

These patterns, although imperfect, are unique to each 3D printer and repeatable. And that’s how, like fingerprints, the 3D printed object can be traced back to the 3D printer that created it.

“3D printers are built to be the same. But there are slight variations in their hardware created during the manufacturing process that lead to unique, inevitable and unchangeable patterns in every object they print,” Xu said.

As part of the study, the research team made 5 door keys from 14 common 3D printers – 10 fused deposition modeling (FDM) printers and four stereolithography (SLA) printers.

Using a common scanner, the researchers created digital images of each key. They, then, enhanced and filtered each image, identifying the elements of the in-fill pattern. Thereafter, the team developed an algorithm to align and calculate the differences in each key to verify the authenticity of the “fingerprint.”

The researchers then created a “fingerprint” database – ‘PrinTracker’ – of the 14 3D printers, and found that they were able to match the key to the 3D printed that created it, 99.8 percent of the time. To determine whether additional use or wear-and-tear of the printers would affect the database, the researchers ran a separate series of tests 10 months later on the same printers and discovered that the PrinTracker’s ability to match objects to their machine of origin were still 99.8 percent accurate.

The team also conducted experiments involving keys damaged in various ways to hide their identity but even then, the PrinTracker was 92 percent accurate in these tests.

The ‘Printracker’ technology or method is similar to the method of tracing a bullet to a specific firearm. When a gun is fired, as the bullet flies down the barrel of the gun, it encounters certain ridges and grooves that cause the bullet to spin and increases the accuracy of the bullet. These ridges and grooves leave unique markings on the bullet and such markings can be matched by the forensic investigators and law enforcement agencies to the firearm that the bullet was fired from.

The research team did not 3D print any guns or counterfeit objects but Xu is confident that PrinTracker can be used to any even those to the 3D printer that created them.

“We’ve demonstrated that PrinTracker is an effective, robust and reliable way that law enforcement agencies, as well as businesses concerned about intellectual property, can trace the origin of 3D-printed goods,” Xu said.

The study was presented in Toronto at the Association for Computing Machinery’s Conference on Computer and Communications Security, which runs from Oct. 15-19.