Field Device Authentication via Signed Query Keys
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Solution Overview
Problem
Existing field devices in process automation lack secure authentication methods that do not require a permanent secure connection to the process control network, leading to high complexity and key management efforts, and risk man-in-the-middle attacks, especially when adding new units or maintaining configurations.
Innovation Solution
A method using asymmetric encryption where a unique random request key is generated in the field device, transmitted to a trustworthy server via a local operating device, and signed with the server's private key, allowing authenticated unlocking while maintaining the existing configuration without needing a secure connection to the process control network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If asymmetric encryption with a trustworthy server is implemented for secure authentication, then security reliability is improved, but device complexity increases due to key management requirements
Solution Approach 1:
A trustworthy server acts as an intermediary between field devices and the process control system. The server stores public keys and verifies signatures, eliminating the need for field devices to directly manage cryptographic keys. This mediator approach maintains security while reducing device complexity.
Solution Approach 2:
The complex key management functionality is extracted from field devices and centralized in the trustworthy server. Field devices only need to generate signatures using their private keys, while the server handles key storage, verification, and distribution, significantly simplifying device architecture.
2Ease of operation
If a RESET button is used to unlock the field device after incorrect password entries, then ease of operation is improved, but loss of information occurs as the device is reset to factory settings
Solution Approach 1:
The trustworthy server acts as an intermediary that verifies the operator's identity through digital signature authentication. When authentication succeeds, the server authorizes the unlocking operation, allowing the device to be reset without permanent configuration loss since the authorized operator can restore settings.
Solution Approach 2:
The system performs preliminary authentication of the operator's identity and authorization level before allowing the RESET operation. This preliminary verification ensures that only authorized personnel can initiate device resets, preventing unauthorized information loss.
3Productivity
If field devices are integrated into a process control network, then productivity is improved through centralized control, but security risks increase due to potential man-in-the-middle attacks
Solution Approach 1:
Traditional password-based authentication mechanisms are replaced with public key cryptography and digital signatures. This substitution provides stronger security against man-in-the-middle attacks while maintaining network integration and productivity benefits.
Solution Approach 2:
The trustworthy server serves as a mediator that verifies digital signatures from field devices before accepting communications. This intermediary verification layer prevents man-in-the-middle attacks by ensuring the authenticity of each communication party, allowing secure network integration.
4Ease of operation
If a local operating device is used to connect to the field device, then ease of operation is improved, but vulnerability to unauthorized access increases without secure connection
Solution Approach 1:
Physical password entry through the local operating device is replaced with cryptographic authentication using digital signatures. The local device can easily connect to the field device, and security is maintained through cryptographic verification rather than vulnerable password mechanisms.
Data Source
AI summary
The invention relates to a method and a device for the secure operation of a field device (110). The core of the invention consists in generating and storing a query key (115) in the field device (110), which is transmitted via a secure connection to a trusted server (220) using a local operating device (130) and the authentication (122) of a local operator (120), and is received back from this trusted server (220) signed as a response key (222).