ECU Message Authentication Using Trip Flags for Counter Resynchronization

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Solution Overview

Problem

Modern vehicle systems with multiple Electronic Control Units (ECUs) face desynchronization issues, which can lead to communication errors and vulnerabilities to replay attacks, especially when synchronization messages are missed or delayed, affecting the processing of authenticated messages.

Innovation Solution

Incorporating a trip flag into authenticated messages and implementing a logic system that compares the trip flag with the latest trip counter value to detect and correct desynchronization, ensuring that messages are processed correctly without causing significant processing delays or errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If synchronization messages are transmitted at periodic intervals, then desynchronization is reduced, but processing delays may occur when messages are missed or delayed

Engineering Contradiction:

Improvesynchronization accuracyVSAvoidmessage processing delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

Instead of requiring full trip counter values for synchronization, the system uses only the least significant bit (trip flag) in authenticated messages. This partial action approach provides sufficient information for desynchronization detection while minimizing communication overhead and processing time, allowing faster detection and correction without waiting for full synchronization messages.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The system changes the parameter used for synchronization from the complete trip counter value to just the least significant bit (trip flag). This parameter change reduces the amount of data that needs to be transmitted and processed, enabling faster detection of desynchronization events and reducing processing delays while maintaining synchronization accuracy.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the trip flag is compared with the trip counter to detect desynchronization, then detection accuracy is improved, but additional processing steps are required

Engineering Contradiction:

Improvedesynchronization detection accuracyVSAvoidprocessing logic complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system extracts only the least significant bit of the trip counter (the trip flag) for inclusion in authenticated messages and for comparison purposes. This extraction approach maintains high detection accuracy by capturing the critical synchronization information while significantly simplifying the processing logic compared to comparing full trip counter values, reducing computational complexity and processing steps.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS11528162B2Detecting and resolving desynchronization of trip counter values in authenticated messages

Publication Date: 2022.12.13 FORD GLOBAL TECH LLC

AI summary

Techniques for using a trip flag to detect desynchronization of trip counter values in a vehicle system. Techniques include a first electronic control unit (ECU) receiving a synchronization message including a trip counter and receiving a message from a second ECU including a trip flag. The trip flag includes a single bit of data generated by the second ECU. The first ECU compares the trip flag to a last bit of the trip counter stored at the first electronic control unit and processes the message in response to the trip flag matching the trip counter. The first ECU compares the trip counter to a previous trip counter based on the trip flag differing from the trip counter. The first ECU processes the message using the previous trip counter or increments the trip counter to process the message based on the comparison with the previous trip counter.