# Potential of Homomorphic Encryption for Cloud Computing Use Cases in Manufacturing
## 4 Use Cases for Homomorphic Encryption for Cloud Computing in Manufacturing
### Predictive Maintenance for SME  
The first use case describes the secure use of predictive maintenance by means of cloud computing and homomorphic encryption in an SME. In the use case considered, the SME is a plastic fiber manufacturer where predictive maintenance is to be introduced for an extrusion process. The manufacturing process of the plastic fiber is a competitive advantage for the SME in this use case, which is why all process data should remain secret. Predictive maintenance is a form of maintenance strategy in manufacturing companies that ensures the availability of machines and systems, guarantees high product quality, and improves overall equipment effectiveness [42, 43]. However, the use of predictive maintenance is not widespread among SMEs, as high costs and computing power are incurred for the development of corresponding maintenance systems. Recording data, conducting test runs, software development, and subsequent validation for the development of such systems take financial and time resources that an SME cannot afford [44]. In addition, SMEs usually do not have the expert knowledge to model such a system or the computing resources needed to implement it [45]. Therefore, the outsourcing of predictive maintenance operations is considered. In this way, the lack of computing resources of the SME can be compensated. By using predictive maintenance as a cloud service, the costly and time-consuming development of an in-house predictive maintenance system is eliminated. This also avoids the need to build up expert knowledge within the company, as the cloud provider offers a ready-to-use predictive maintenance solution. Due to the size of the company (SME) and the general goal of cost savings, the public cloud is chosen as the cloud type. Cloud computing, is therefore, primarily used for data management and because of its flexibility. Fully homomorphic encryption is applied as the data model requires both addition and multiplication operations (only operations possible with FHE, see Section 2.2.2) and has no defined number of calculations. The selection of  
Figure 6: Identification of use cases. these characteristics is shown in the morphological box of the predictive maintenance use case in Figure 7.  
The case also fulfills the requirements security, time, and cost. First, the data are highly sensitive for the company's business model, are analyzed by a third party, and must be secure of the whole data life cycle. Second, the planned predictive maintenance applications do not require real-time information; instead, maintenance requirements are queried at specific time intervals. Third, since the development of a predictive maintenance system can be avoided with the help of the cloud and, since a relatively inexpensive public cloud is selected, the cost requirement is also met. The cloud architecture of the predictive maintenance use case is also shown in Figure 7. It shows the basic data and information flows between the SME and the cloud, the recording and processing of the information, and the encryption and decryption of the data. First, measured values are recorded on the extruder during the extrusion process, and a time series of condition data is generated in this way. Different status data such as process temperature, raw material flow, and coil speed are recorded, which are necessary as input for the predictive maintenance model. Since, as defined at the beginning, all data must remain secret, the measured values are homomorphically encrypted by the SME. The encrypted data are then transferred to the cloud, which also contains the cloud provider's predictive maintenance model. The model is then calculated in the cloud using the SME's input data. Since both the data and the model are homomorphically encrypted, the calculation can take place on the encrypted data; hence, in-use data are used in an encrypted manner, and end-to-end data security is ensured.