# A Review of Industry 4.0 Manufacturing Process Security Risks
## 3 Identifying the Problem
### The Problem in the Context of Industry 4.0
#### 3.4.4 CAD Model Security Gaps  
Many industrially manufactured products have their roots in a CAD model that has been designed by an engineer or draftsman according to the required specifications. The CAD model is therefore the first step in a series of processes known as the \"digital thread\" [8; 41], as illustrated in Figure 6 below. Once CAD 3D modeling of a product has been completed, the 3D model is converted to a file that contains all of the details of the model's design in a format that can be interpreted by the applicable manufacturing hardware. This particular file is in a format known as the stereolithography (STL) file format, which contains approximations of all the surfaces of the CAD model by means of triangles. In the case of an additive manufacturing process such as 3D printing, the product is manufactured in layers that are tightly packed on top of one another. The conversion from the STL file format to the layered format of the CAD model is known as \"slicing\", and is performed by a utility called a \"slicer\". The slicing process involves generating sets of 2D slices that are essentially sets of intersecting points between the 3D model and the slicing plane. This 3D model is then manufactured one layer at a time. This process can be represented mathematically [42] as  
\[S=\left\{S_{i}\middle|\;i\in[1,N]\right\}\]  
where \(S\) represents the set of \(N2\)D slices. Furthermore, each slice can be mathematically described as  
\[S_{i}=\left\{p_{i,j}\middle|\;j\in[1,\;|S_{i}|]\right\}\]  
where \(|S_{i}|\) represents the number of intersecting points \(p_{i,j}\) in slice \(i\) at the \(j\)th point, represented by a coordinate pair \(\left(x_{i,j},y_{i,j}\right)\). Once the STL file has been processed by the slicer, it can be sent to the manufacturing hardware's interface so that it can be interpreted and converted into machine code that controls the manufacturing hardware. Finally, the machine code that is executed is translated into commands to the actual components of the manufacturing hardware that produces the final product. In Section 2.2, the fact that many OT devices and platforms do not have adequate security measures in place, was discussed. With this in mind, it can be deduced that there are several possible attack vectors in the digital thread illustrated by Figure 6. For example, it is possible to alter the design of the final product by compromising the CAD model through malicious changes to the intended CAD model design. The STL and slicer output files can be intercepted, and several changes can be induced that could compromise the structural integrity of the final product. Such changes can be subtle enough to  
Figure 6: Digital thread for the manufacturing of a three dimensional (3D) modeled product. STL: stereolithography  
remain undetected to perhaps even the informed eye. Furthermore, the control interface of the additive manufacturing hardware can be hacked, and machine instructions can be altered to command the equipment to operate outside certain limitations and parameters, or execute unauthorized commands during operation (recall the Maroochy Shire sewage spill example from Section 2.1). It is also apparent that the three CIA pillars (confidentiality, integrity and availability) are at risk of being compromised at various points throughout the digital thread. Consider, for example, the design of a proprietary product through CAD modeling. The design engineer or draftsman is authorized to have access to the product's CAD model. Since any information on the product is of a sensitive nature, access to this information needs to be controlled, especially when the product's design is distributed to the manufacturer. It should be securely stored on the computing platform on which it has been designed, and access to the design information should be restricted to only authorized parties.