Similar to the way each person has a set of exclusive fingerprints, the extruder head of a filament 3D printer has a unique temperature curve. That’s the hypothesis of researchers at the State University of New York (SUNY) at Buffalo in their recent paper, “ThermoTag: A Hidden ID of 3D Printers for Fingerprinting and Watermarking,” published in the journal IEEE Transactions on Information Forensics and Security. The thermodynamics of the extruder head, dubbed its “ThermoTag” by the researchers, puts a stamp undetectable to the naked eye on the physical properties of parts it prints.
If proven and accepted through additional research, the phenomenon has implications for thwarting counterfeiting of parts and products, protecting intellectual property (IP) and tracing illegal manufacturing of weapons. With 3D printing increasingly used for medical devices and also by SpaceX to make rocket parts, GE for aircraft engines and the U.S. Navy for a submarine’s hull, the safety and national security implications of faulty or counterfeit parts, or both, are enormous.
Some current methods of protecting IP and ensuring authenticity include laser engraving a QR code on parts and products; injecting nanomaterials into them, creating tiny voids in the design; and including near-field communication (NFC) tags with digital information.
Unfortunately, some methods require costly devices to scan a part or may cause physical defects in the part. The ThermoTag offers a cheaper, safer, more secure option, according to the researchers. “The hot-end-based ThermoTag fingerprints can be easily obtained through temperature sensing and used as the 3D printing watermarks, safer than using extrinsic elements or random numbers, and more efficient than introducing PUFs (physical unclonable functions, such as in integrated circuits for security) into 3D printed products,” they wrote. “The unique features of hot ends are caused by manufacturing imperfections and system variations, which are hard to identify, predict, and clone.” A drawback is that temperature curves for the same hot end may change as the printer is used; the melted filament starts to coat the area and may not be fully cleaned off. Thus, the temperature curve for the hot end would have to be calibrated periodically.
So far, the ThermoTag idea is supported by limited research data from 45 different extruders of the same model, which led to correct identification of the source printer with 92 percent accuracy, according to the paper. Each filament 3D printer has an extruder that pushes the building material along. The extruder’s hot end then melts the material and places it on the print bed to build a part. “This is definitely not large enough (of a sample size) to make it a real-world application,” said Zhanpeng Jin, an associate professor at SUNY Buffalo, who led the research. “Just like 100 years ago people found that fingerprints might be different for different people and started with a sample size of 100 (for example), later on they grew the group to increase the confidence.”
Jin proposed encoding the extruder’s temperature curve data in CAD files as a “watermark.” Watermarks included in CAD files are visible and removable, but an identifier based on Jin’s group’s idea would make the watermark more secure. If the extruder data in the watermark doesn’t match up to the printer used to legitimately make the part, it would be a fake. Printer manufacturers would keep a database related to the extruder’s temperature curve on their products and provide it to buyers.
In a scheme reminiscent of two-factor authentication, Jin proposes adding a second bit of unique data to the watermark. The designer’s signature could also be encoded in the file to make security more robust. Alternatively, in the future a 3D mesh model-based blind watermark technique could provide a more secure fingerprint.
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