Joel Zlotnick, Elizabeth Gil, Jordan Brough and Troy Eberhardt

In recent years, 3D printing technologies have been increasingly adopted for a wide range of product development and manufacturing applications. More widespread public availability of 3D printing can be anticipated in the future, including in home/office environments. Just as the widespread availability of low-cost inkjet devices permanently changed the counterfeiting landscape in the late 1990s, 3D printing will also be used for criminal activities, including document counterfeiting. Just as digital counterfeiting drove evolution in document design practices and development of new security features, 3D printing and its potential as a counterfeiting threat can be addressed through both anti-counterfeiting technologies and purposeful security design. This paper summarises some capabilities of 3D printing, anticipates counterfeiting applications, and presents strategies to mitigate future counterfeiting risks posed by 3D printing.

3D printing
The term ‘3D printing,’ also called additive manu­facturing, refers to a set of diverse technologies capable of creating objects from metals, plastics or other raw materials without the use of conventional fabrication processes such as drilling, machining, or injection molding. For example, Figures 1 and 2 show a simple object produced by a type of 3D printing called fused filament fabrication, in which spooled polymer raw material is extruded from a heated printhead. Other types of 3D printing have different capabilities and outputs. Compared to conventional manufacturing, advantages of 3D printing can include reduced raw material and energy consumption, rapid and inexpen­sive prototyping, high potential for customisation, on-demand local production, a small printer footprint, and printing of complex multi-material structures for which no conventional manufac­turing pathway even exists. These advantages drive proliferation of 3D printing for many micro and macro applications, including consumer objects, parts and tools, medical, entire buildings, and even 3D printing of 3D printers. Hobbyists have already embraced 3D technology. This paper discusses just a few possible ways this rapidly evolving technology might eventually affect the security document landscape.

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Figure 1: This object is a 3D printer test pattern, printed by fused filament fabrication, which is composed entirely of one blue polymer. More complex 3D objects are possible that incorporate multiple materials.
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Figure 2: Magnified view of a portion of the printer test pattern shown in Figure 1. This 3D printer has a different resolution on the Z axis (layer thick- ness) than in the X and Y axes (printhead size). Resolutions will undoubtedly improve in future generations of 3D printers.

3D printing and security documents
Two questions could be asked in relation to security documents: first, can 3D printing contribute to the production of genuine security documents, and second, does 3D printing represent a counterfeiting threat? Possible answers to the first question may seem unrealistic compared to current document issuance practices. For example, imagine an identity card sub­strate with a window, tactile features and complex internal structure manufactured at issuance locations directly from raw polymer, from a proprietary digital template that prints the card body and personalisation simultaneously. The need to trans­port and store blank cards, or maintain a centralised factory line for their manufacture, could be eliminated. Just because this and other concepts are theoretically possible does not mean they are practical today or superior to conven­tional production and issuance workflows. 3D as a tool for genuine document issuance requires its own analysis. Accordingly, this paper will address counter­feiting risks from a theoretical and future-oriented viewpoint, assuming that 3D printers of tomorrow will be superior in both resolution and material handling to those of today.

Counterfeiting applications of 3D printing might be grouped into two categories: augmentation of traditional counterfeiting workflows and direct digital manu­facturing of counterfeits or parts of counterfeits. These alternatives will be explored below. The final two sections of this paper outline strategies for mitigation of risks presented by 3D counterfeiting.

Supplementing traditional counterfeiting methods
An important industrial use of 3D printing is the rapid on-demand production of custom tools, molds, and machine parts to support high volume fabrication work­flows. The 3D printer does not produce a final product directly, but makes components for an assembly line or machinery that does make the product. In the context of traditional (non-digital) counterfeiting, imagine 3D printing used to manufacture counterfeiting equipment like letterpress numbering elements, intaglio printing plates, watermark dies, embossing devices, stamps, and parts for printing presses. The question is whether 3D printing introduces advantages over existing non-3D traditional counterfeiting processes. This question is complex and cannot be answered comprehensively here, but consider the manufacturing of an intaglio print plate as just one illustrative example.

Traditionally, hand engraving techniques (Figure 3) have provided security designers with a high degree of control over both the width and depth of intaglio lines.

Figure 3: Hand engraved intaglio plate, showing graver marks within the line recesses. This method provides an artist with good control over both the width and depth of engraved lines. Coaxial light, compare to Figure 5.

The addition of high-tech digital platemaking techniques allow for even more detail (Figure 4).

Figure 4: The text in this banknote was embossed during the same printing step that deposited the nearby black intaglio ink. Detail this fine requires sophisticated digital platemaking techniques capable of engraving the tiny text inside larger intaglio engravings. Oblique light.

In contrast, acid etching of intaglio plates (Figure 5) is popular with counterfeiters because it is easier and cheaper.

Figure 5: Acid etched intaglio plate, showing smooth line edges and no graver marks in the recesses. The acid etches the sides of the lines at the same time it etches depth, limiting control over line quality. Coaxial light, compare to Figure 3.

However, some control over line quality is lost because acid etching creates an undesirable increase in line width when trying to achieve the same depth created by hand engraving. Additionally, multiple acid etching steps are necessary for the plate to feature varying line depths. Because 3D printing is also a relatively inex­pensive technology but potentially offers more control than acid etching, 3D printing might be used for counterfeit intaglio plate manufacture, either now or in a future when 3D printer resolutions have improved. Similar comparisons could be done for other traditional counterfeiting techniques to identify how 3D printing might shine, to the general conclusion that 3D can provide advantages in a variety of circumstances.

Finally, through programs such as Project Genesius and Operation Genesius, law enforcement agencies partner with private sector printing equipment suppliers to combat counterfeiting. It is unclear how this mission might change in a future where parts for printing devices, or even entire printing devices, could be 3D printed instead of purchased.

Digital counterfeiting in 3D
The previous section explored potential uses of 3D printing to supplement traditional counterfeiting work­flows, but 3D printing could also be used for direct counterfeiting of documents. The scope of possibilities is broad, and could include anything from basic tactile feature simulations to 3D counterfeiting of entire plastic card bodies. The following example illustrates how UV-cured inkjet, just one of many diverse 3D printing technologies, has already been used for simulation of tactile features on counterfeit identity cards otherwise manufactured using non-3D processes.

For decades, counterfeiters have simulated texture features using thermography (Figure 6), dry embossing (Figure 7), and other analogue methods; use of ultra­violet (UV)-cured inkjet is a more recent development.

Figure 6: Intaglio texture simulated by melting of transparent thermographic powder over a planar offset image. 
Figure 7: Intaglio texture simulated by dry embossing over planar offset graphics. Because two printing steps are involved, the embossing and offset image are not in register. Oblique light.  

The printing mechanism of UV-cured inkjet is similar to conventional inkjet, but the ink formulations and drying mechanisms are different. Conventional inkjet inks are typically water- and/or solvent-based, and dry by absorption and evaporation. In UV-cured inkjet, the liquid ink is exposed to UV illumination immediately after printing, causing the droplets to harden into a microscopic tactile structure.

As above, the question is whether UV-cured inkjet provides counterfeiters with new capabilities when compared to conventional analogue methods of texture simulation. Because UV-cured inkjet produces textured graphics in a single printing step (Figure 8), it eliminates registration errors that occur when printed graphics and texture are simulated in two separate steps (for example, the misalignment of the image and embossing in Figure 7).

Figure 8: Tactile laser engraving texture simulated by UV-cured inkjet. The image and texture are produced in a single printing step, just as in tactile laser engraving or intaglio printing. Coaxial light.    

Further, UV-cured inkjet can print tactile layers that are clear (Figure 9) or even white (Figure 10), which are not possible with conventional 2D inkjet.

Figure 9: Lamination plate clear tactile feature in a genuine card (left) and a clear tactile simulation of the feature by UV-cured inkjet (right). Future generations of 3D technologies will be capable of finer detail. Oblique light.    
Figure 10: Opaque white text on a plastic card, printed by UV-cured inkjet. Unlike most conventional 2D inkjet printing, UV-cured inkjet is capable of clear or white print.  

However, UV-cured inkjet is similar to 2D inkjet in that it relies on CMYK (cyan, magenta, yellow and black) to simulate spot colours (Figure 11), so CMYK UV-cured inkjet could still be detected in counterfeits by looking for a pattern of coloured dots.

Figure 11: Lamination plate clear tactile feature and black tactile laser engraving in a genuine card (left), and simulations by clear and CMYK UV-cured inkjet (right). The presence of CMYK instead of spot colours can make counterfeit detection easier. Oblique light.    

Looking past the simulation of tactile features alone, UV-cured inkjet is likely not suitable for counterfeiting more complex 3D objects, such as a complete card body. However, other 3D printing technologies may eventually have the potential to simulate entire plastic card documents, including artwork, personalisation, tactile features, windows, complex multicolour sub­strates and even polymer passport data page hinge fabrics. Also consider the future potential of 3D printing to simulate a complete security paper substrate, including texture, security fibres, a security thread and a watermark image, all manufactured in one pass from a single device.

Though these potential applications for 3D printing should not be trivialised, these attacks are likely not feasible, practical, or economical at the current time and are presented mainly to stimulate thought about future possibilities. The complexity of genuine document design and production should be maximised to counter the inherent limitations of 3D printing technologies. Many security design strategies and existing optical, physical, and chemical security features, already employed to combat conventional counterfeiting, are likely to be equally effective against 3D counterfeiting. The reasons include both physical and conceptual limitations of 3D printing.

Designing to exploit physical limitations of 3D
Generally, many security design practices are defined by the limitations of various traditional and digital counter­feiting methods. Consider one common security design practice that only exists because it exploits an inherent limitation of digital counterfeiting technologies. Micro­printing (Figure 12) is often included in security artwork specifically because most inkjet and toner devices have difficulty replicating small details (Figure 13). Given this knowledge, how can security design practices exploit the weaknesses of 3D printing hardware capabilities?

Figure 12: Offset microprinting in a genuine security document.  Microprinting is not a strong defense against traditional counterfeiting, but fights digital counterfeiting because it exploits resolution limitations in digital printing devices. Compare to Figure 13.  
Figure 13: Simulated inkjet microprinting in a counterfeit. Most commercial inkjet printing devices were never intended to replicate detail this fine. Compare to Figure 12.

Just as most inkjet printers can only print from four ink cartridges simultaneously, 3D printers only print with a limited number of raw materials simultaneously (spools of plastic filament of various colours, for example). Sophisticated 3D printers can integrate the output of five or more such spools into a single cohesive object, but many security documents contain far more than five colours/materials, including substrate components, ink colours in visible and UV, and more. Complete simulation of a security document containing a variety of components of different colours and diverse optical, physical, and chemical properties using just a few 3D materials would be challenging, and of very limited quality. Counterfeiters using 3D printing might find shortcuts to simulate colour, just as inkjet counterfeiters use CMYK halftones to simulate spot colour line art. However, a document with many complex security features can force counterfeiters to merge 3D printing with entirely different technologies to simulate colour shifting effects, optically variable devices, UV features, etc. For this reason, counterfeiters may find it difficult or impossible to rely on 3D printing alone.

Designing to disrupt prepress workflows in 3D
Barriers to counterfeiting include not only the tech­nological barriers described above, but also conceptual and design barriers such as understanding how a genuine document is constructed or how counterfeiters simulate or replicate artwork. Complex design can help deter even sophisticated traditional counterfeiters that possess strong graphic arts skills. This is true not just for 2D artwork, but also for 3D aspects of a document’s construction. An example using offset and intaglio printing will be illustrated and then extrapolated for security design suggestions relevant to 3D printing.

Complex design features like offset line artwork (Figure 14) and offset security halftones (Figure 15) can be tedious to replicate accurately, but offset cannot print ink layers of different heights, so the artwork in Figures 14 and 15 can only be produced in 2D.

Figure 14: Offset line artwork, showing high consistency in ink layer thickness. Certain areas of the overall image look darker because the lines are wider, and other areas look lighter because the lines are narrower. Compare to Figures 15 through 17.  
Figure 15: Offset security halftone design, showing high consistency in ink layer thickness. As in Figure 14, some halftone elements appear darker primarily because they contain wider lines, and halftone elements with thinner lines look lighter. Compare to Figures 14, 16, and 17.

In contrast, intaglio engravings can be of varying depth, allowing an intaglio plate to print a range of ink layer heights, and therefore a range of visible colour satura­tions. Unlike the offset in Figures 14 and 15, the intaglio in Figures 16 and 17 appears to have more than one ink colour because the designer also customised plate engraving depth and ink layer height, not just 2D artwork.

Figure 16: Intaglio line artwork, likely printed from a single plate and one ink colour, but visually displaying both dark green and light green. Darker green areas are thicker ink printed from deeper engravings, and the lighter green is thinner ink printed from shallow engravings. Compare to Figures 14, 15 and 17.  
Figure 17: Intaglio security halftone, likely printed from a single plate and one ink colour, but showing various colours of blue. Unlike Figure 15, the apparent colour of the numerals is determined not only by line width, but also the engraving depth and ink layer thickness. Compare to Figures 14 through 16.  

For a high quality intaglio counterfeit, the counterfeiter would have to replicate both the line artwork (2D) and multiple engraving depths (3D), which is harder than counterfeiting the 2D art alone. Counterfeiting of 3D intaglio artwork using a 2D offset process is likely to negatively affect the tonal range of the image, the integrity of the line artwork, or both.

The above comparison is a specific example of a more general concept, which is designing in 3D as well as 2D. Access to 3D printing technology is not the same as the ability to reverse engineer a document to produce the 3D digital models required to drive a 3D printer. Though document issuers can neither control proliferation of 3D printing technology nor completely prevent its use in counterfeiting, security documents can be made conceptually challenging to reverse engineer, minimising the potential of 3D printing for counterfeiting. For each facet of a genuine document’s production, this can be achieved in numerous ways and is not limited to the example of intaglio described above. Using an identity card substrate as one example, contemporary strategies already include distribution of visible and UV art throughout multiple substrate layers, multicoloured substrate layers (Figure 18), multilayer windows (Figure 19) and visually complex tactile features (Figure 20), all of which increase the challenge of reverse engineering the 3D card structure in addition to its 2D artwork.

Figure 18: Laminated plastic layers in a card body can be customised by opacity, colour, thickness, placement, and other characteristics to make the 3D structure of the card body more difficult to reverse engineer. The corner of this card body shows clear, white, and red layers.  
Figure 19: Two layers in this passport data page body contain clear windows of different placement, shape, and size. This increases the 3D complexity of the data page body and allows printed images to be placed and viewed on surfaces inside the structure of the plastic. 
Figure 20: Tactile lamination plate features can be optimised for both tactile and visual complexity. The tactile feature on this card contains nonrepeating line art, microprinting, variable height, contrast between matte and gloss finish, and more. Coaxial light. 

Conclusion
The impact of 3D printing on the counterfeiting environ­ment has been minimal to date, and its full potential may not be realised until improved generations of 3D printing devices are more widely available. In the future, 3D printing technologies might either play a supporting role in existing counterfeiting workflows or could also be used for direct simulation of security document components and features. Just as with any other material or technology available to counterfeiters, 3D printing should be viewed within the context and limitations inherent to counterfeiting workflows. The counterfeiting threat posed by a new technology can be addressed through security design practices that merge genuine document components, manufacturing processes, and personalisation technologies such that these elements become inseparable from one another, and which link physical manufacturing and artwork re-origination problems so that counterfeiters cannot solve these separately.

MORE ABOUT THE AUTHORS

Joel Zlotnick is employed by the US Department of State, Bureau of Consular Affairs, Counterfeit Deterrence Laboratory as a physical scientist. He conducts research on how design strategies can help maximise the security value of printing technologies and security features, and develops training programmes on counterfeit detection.

Elizabeth Gil is employed by the Homeland Security Investigations Forensic Laboratory as a forensic document examiner. Elizabeth divides her time between conducting examinations on travel and identification documents and testing security documents for vulnerabilities.

Jordan Brough is employed by the Homeland Security Investigations Forensic Laboratory as a forensic document examiner, specialising in adversarial analysis and counterfeit deterrence. Jordan spends his time examining suspect documents and consulting with United States security document designers.

Troy Eberhardt is employed by the US Immigration & Customs Enforcement Homeland Security Investigations Forensic Laboratory. He supervises the Research and Development Section at the laboratory, which specialises in identifying and mitigating vulnerabilities within travel documents.

References

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6 U.S. Immigration and Customs Enforcement. (2018). ICE. [Accessed April 26, 2019].