# Secure and Privacy-Respecting Documentation for Interactive Manufacturing and Quality Assurance
## 6 Application and Results  
The work presented in this paper was prototypically integrated into a manual assembly workstation and can be applied to a multitude of real-world use cases. In this section we describe the proof-of-concept application of a safety-critical screw connection and briefly discuss the benefits of 4 Crypt compared to the basic system design presented in Section 2 as well as previous proposals. Safety-critical screw connections occur in many production processes, for example in the manufacturing of vehicles such as cars and planes. These types of screw connections need to be executed by qualified workers using the right tools with the correct settings (e.g., the right amount of torque). As an automated documentation and workflow recognition system, the 4 Crypt system presented in this paper can provide an invaluable instrument to supervise and document the correct execution of these safety-critical work steps. For this, both our basic system design (c.f. Section 2) and the extended system design (c.f. Section 4) include components for worker authentication, workflow recognition and video documentation. However, only the extended system design encrypts captured videos and provides an interface for the worker to verify the integrity of the included privacy-protection mechanisms. In any case, workers first authenticate and log in to 4 Crypt by holding their personal smartphone on the NFC-reader near the assembly station. By authenticating the worker prior to any work step, we can determine if the executing worker is indeed qualified for the task at hand. Simultaneously, a TPM-based remote attestation protocol is conducted over the same NFC connection. During this attestation process, unique fingerprints of the assistance system's current software configuration are transmitted to the worker's smartphone. By comparing the fingerprints to expected \"good\" values, the smartphone notifies the worker if the privacy-protection mechanisms of the assistance system can be trusted. Only if these checks are successful, are the cameras activated and the worker steps in front of the assembly station. During the conducted work step, the captured video feed is analyzed by the workflow recognition component and synchronized with a model of the expected workflow. That way the assistance system can warn the worker if an important work step is missed or executed incorrectly. In case of a safety-critical screw connection, this could happen if the worker leaves out some screws, forgets to properly tighten them after placement, uses an unsuitable wrench for the work step, or grabs the wrong kind of screws from the shelf. Furthermore, the system creates a textual documentation of the performed work steps for the supervisor and retains the encrypted video feed in case of a complaint. As described in detail in Section 4, decryption of the retained video file is only possible if the corresponding worker and at least one of the employee's trusted representatives consent to the disclosure by placing their respective smartphone and/or smartcard on the assembly station's NFC-reader. In comparison with previous approaches, our system stands out primarily in the way it provides strong privacy guarantees for workers. While most existing video documentation systems do not include privacy-protection components at all, there are some proposals for more privacy-friendly smart manufacturing environments. These approaches often include data obfuscation and anonymization schemes [30], retain decentralized data access logs [31], or define privacy best practices (privacy-by-design) when designing assistance systems for smart production facilities [32]. However, in all cases it requires trust in the efforts of the system operator to design and deploy a privacy-respecting smart manufacturing system. As we motivated in Section 3, this assumption is often unsound since there are clear conflicts of interests between the employer as system operator and the workers.