# Potential of Homomorphic Encryption for Cloud Computing Use Cases in Manufacturing
## 3 Encryption for Cloud Computing in Manufacturing
### Limitations of Classic Encryption for Cloud Computing  
To ensure comparability with other technologies, a scenario for the use of cloud computing is introduced. In this example, a company is assumed to use a cloud service for the storage and processing of data collected in manufacturing. These data are transferred from the on-premise company IT to the cloud in the form of a database and stored there. The following use cases should be possible: backing up encrypted manufacturing data as a database in the cloud; performing analyses using the data of the stored database.  
The cloud computing scenarios for the two manufacturing use cases are shown in Figure 3. The potentials (green) and limitations (orange) are highlighted.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**HE Category** & **Partially HE** & **Somewhat HE** & **Fully HE** \\ \hline Possible operations & Addition OR & Addition AND & Addition AND \\  & multiplication & multiplication & multiplication \\ Operations amount & Unlimited & Limited & Unlimited \\ Calculation effort & + & ++ & +++ \\ Security & ++++ & ++++ & ++++ \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characterization of homomorphic encryption categories.  
Figure 3: Limitations of classic encryption during cloud computing.  
In scenario 1 (data backup), the data are encrypted at the company and transferred to the cloud. It is noticeable that no limitations occur in the pure storage of data using classic encryption methods. The database is encrypted during data transfer and data storage in the cloud. Thus, the data are secure over the entire data lifecycle. This means that classic encryption is fully suitable for data backup. For scenario 2 (data analysis), two possible variants exist. In variant 1 of scenario 2, the analysis is performed in the cloud. For the analysis to be possible, the encrypted database must first be decrypted in the cloud as it is not possible to analyze classical encrypted data (see Section 2.2.1). The result of the analysis is then encrypted in the cloud again and transferred back to the company. The company finally decrypts the result of the analysis for on-premise use. As the data analysis is carried out in the cloud, the company relies on the flexible computing resources of the cloud, which is a benefit. However, since the database is decrypted in the cloud at this point, data security is not guaranteed over the entire data lifecycle. In variant 2 of scenario 2, the analysis is carried out on premise. Here, the backed up encrypted database is first downloaded on the company's on-premise IT. Here, the database is decrypted to perform the analysis.  
To have an updated backup, the result is then encrypted again and stored in the cloud. In this variant, data security is guaranteed throughout the whole lifecycle as the decrypted data are only on premise and, thus, only visible to the company. However, as the analysis is not carried out in the cloud, the computing resources of the cloud are not utilized. Furthermore, since the database must be downloaded from the cloud before each analysis, the amount of transferred data is constantly increasing. This analysis shows how the central limitation of classic encryption, i.e., not being able to use in-use data, affects the security of cloud computing: either the company relies on cloud resources with the risk of revealing the data, or the data are secure while cloud resources are not used. Pure data backup, however, has no limitations with classic encryption methods.