# Using Blockchain to Protect 3D Printing from Unauthorized Model Tampering
###### Abstract  
As three-dimensional (3D) printing technology is widely used, security issues have arisen, especially in the terminal parts of automobiles, aircraft, and 3D-printed military equipment. If the original design models or the STL (stereolithography) files are hacked or tampered, severe consequences can be anticipated. In this paper, we propose a demonstration to use a high-throughput blockchain to store the \"fingerprints\" of the 3D model and verify the \"fingerprints\" before printing to prevent illegal tampering. Relying on the tamper-resistant features of blockchain, the security of the model and the credibility of the terminal components can be ensured. The combination of blockchain and 3D printing will help people to build a trusted manufacturing environment and realize a more flexible manufacturing for future industry.  
STL file; copyright protection; blockchain; sharding; additive manufacturing +
Footnote †: journal: Applied  
UAV (unmanned aerial vehicle), causing it to fall in a short time [9]. The accidents caused by abusing additive manufacturing are far more than this. A large number of printed counterfeit products will not only lead to great harm to the original creators and designers but even endanger the entire additive manufacturing industry. How to effectively reduce counterfeit products and protect the intellectual property rights of STL model files become major problems in the current additive manufacturing industry.  
Currently, there are two main ways to realize 3D printing anti-counterfeiting (Figure 1). One is by physical methods, including using fluorescent substances to incorporate printing materials [10; 11; 12], label implantation [13], etc. However, these methods all require special equipment for scanning/reading (e.g., X-rays or ultraviolet devices) and the verification process is cumbersome, time-consuming, and costly. Another anti-counterfeiting idea is focusing on model files. Digital watermarks can be embedded into the models directly [14], including 3D visible digital watermarks [15; 16] and invisible watermarks [17; 18]. However, 3D printers with different precisions will affect detection [19] and the detection process of these watermarks is also cumbersome. Generally, grid reconstruction or printing directions are required to obtain the printing direction according to print traces to see the watermarks [19]. In fact, the above anti-counterfeiting works mainly focus on protecting printed items. Due to the process of a product involving multiple segments, it is not enough to just protect the final step. The digital model files may also be forged quite easily. These methods are invalid once unauthorized model tampering happens. If the upstream has been an intrusion, it will be useless for the downstream to do more work. From the perspective of protecting the whole industrial chain, it is crucial to pay close attention to STL files at the beginning.  
To explore a better way to protect digital model files at the upstream, we propose to use blockchain technology to ensure STL model printing is authentic and credible from the source.