Field Device Access Keys With Device-Specific Time-Limited Hashing

The patent segments the universal access concept into device-specific access keys. Each field device has its own unique access key generated by hashing a manufacturer-specific secret with the device's identification feature. This segmentation allows access control to be tailored to each individual device while maintaining the convenience of a standardized access mechanism across the manufacturer's product line.

The patent applies local quality by making each access key unique to its specific device through the use of device-specific identification features (such as serial numbers or device IDs) in the hashing process. This ensures that the security properties are localized to each device, preventing universal unauthorized access while maintaining ease of operation for authorized users on each specific device.

The patent implements preliminary action by pre-generating access keys with embedded time validity information during device manufacturing or initial setup. The access key includes or is associated with validity period data, so that when the key is presented for authentication, the system can automatically verify both the key's correctness and its temporal validity without requiring complex real-time key generation or external validation infrastructure.

The patent uses a hashing function as an intermediary mechanism to generate access keys from manufacturer secrets and device identification features. This intermediary process simplifies the overall system by providing a deterministic, reversible (in the sense that the original inputs can be recovered if needed) method for key generation that balances security requirements with implementation simplicity. The hash function acts as a mediator between the need for secure, unique keys and the desire for manageable system complexity.