Safety PLC Network Authentication Using Multi-PLC Proof-of-Work
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Solution Overview
Problem
Industrial safety systems are vulnerable to cyber-attacks that can compromise safety PLCs, leading to unintended responses and increased risk of accidents or disasters.
Innovation Solution
Implementing a secure network of safety PLCs with multi-PLC verification and authentication challenges, requiring a majority of PLCs to verify a programming application before allowing reprogramming, using proof-of-work (PoW) to authenticate and protect against malicious attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If safety PLCs are made reprogrammable to allow updates and improvements, then adaptability and functionality are improved, but vulnerability to cyber-attacks and unauthorized modification increases
Solution Approach 1:
The system divides the authentication process into multiple independent verification stages across multiple PLCs. Instead of a single point of reprogramming, the system segments the control function across N PLCs where each PLC independently verifies authentication challenges, creating multiple security checkpoints that must all be compromised for successful unauthorized reprogramming.
Solution Approach 2:
The system introduces an intermediary authentication mechanism between the programming application and the safety PLCs. This intermediary layer implements proof-of-work verification and multi-PLC consensus checking, acting as a mediator that prevents direct unauthorized access while allowing legitimate reprogramming through verified authentication protocols.
2Reliability
If multi-PLC verification is implemented to enhance security, then protection against cyber-attacks is improved, but system complexity and authentication overhead increase
Solution Approach 1:
The system changes the authentication parameter from simple credential verification to proof-of-work computational challenges. By transforming the authentication requirement into mathematical proof verification, the system enhances security through computational difficulty while maintaining relatively simple verification logic in each PLC, balancing security improvement with acceptable complexity.
3Reliability
If proof-of-work authentication challenges are required for reprogramming, then protection against malicious applications is improved, but time required for legitimate programming updates increases
Solution Approach 1:
The system applies partial verification by requiring only N/2 + 1 out of N PLCs to successfully verify the authentication challenge. This partial action approach provides sufficient security protection without requiring all PLCs to complete verification, reducing the total time overhead while maintaining robust protection against malicious attacks.
Data Source
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AI summary
Network of safety PLCs employs multi-PLC verification of a programming application before allowing the application to reprogram any PLC on the safety network. Each PLC on this network is equipped with authentication capability that detects attempts to reprogram the PLC and issues an authentication challenge requiring the programming application to process a proof-of-work. This challenge is also sent to other PLCs on the network along with the response from the programming application for verification purposes. The other PLCs process the challenge and check the response from the programming application for acceptability. If a majority of the PLCs on the network determines the response from the programming application is correct, then the programming application is verified and may proceed with the reprogramming. Such group authentication requires a malicious application to hijack multiple PLCs concurrently on the safety network, a highly unlikely outcome, before reprogramming any PLC.