Safety Critical Control via Keyword Verification

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Solution Overview

Problem

Conventional safety-critical systems require complex and costly duplication of hardware and communication paths to ensure high integrity and availability, which is not necessary if the executive signal is correctly verified, leading to increased system complexity and cost.

Innovation Solution

A system that uses a single low-integrity transmission path to send a plurality of decrypt keys or keywords, with high-integrity key safe switches that compare received keywords to ensure correct execution of safety-critical operations, reducing the number of transmission channels and system complexity while maintaining safety integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multiple high-integrity transmission paths are used to deliver executive signals, then system reliability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvesystem integrityVSAvoidnumber of transmission channels

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The transmission path is segmented into two distinct functional portions: a low-integrity portion for transmitting decrypt keys and a high-integrity portion for storing and comparing keywords. This segmentation allows each portion to be optimized for its specific function, reducing overall system complexity while maintaining security integrity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Keywords serve as an intermediary element between the transmitted decrypt keys and the executive signal generation. The keywords are stored in high-integrity memory and used by key-safe switches to verify commands, acting as a mediator that ensures integrity without requiring multiple high-integrity transmission paths.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If hardware duplication is implemented to ensure high integrity, then system reliability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvesafety integrityVSAvoidsystem cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

High integrity requirements are applied locally only where absolutely necessary - specifically in the keyword storage memory and key-safe switch comparison logic - rather than throughout the entire transmission system. The transmission portion can use lower-integrity, lower-cost components while maintaining overall system safety through the localized high-integrity verification mechanism.

Inventive Principle:

Principle #3Local quality

3Reliability

If multiple transmission paths are used for executive signals, then system availability is improved, but system complexity increases

Engineering Contradiction:

ImproveavailabilityVSAvoidnumber of communication paths

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Keywords are pre-loaded into high-integrity memory in the operative portion before operation begins. This preliminary action ensures that the verification mechanism is already in place and does not require complex real-time coordination between multiple transmission paths, simplifying the communication architecture while maintaining availability.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2534543B1Control of safety critical operations

Publication Date: 2019.04.10 BAE SYSTEMS PLC

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AI summary

A system wherein control of a safety-critical system operation is effected by sending a plurality of keywords via a low integrity transmission means.