CAN Bus Message Authentication Using Propagation Time Difference
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Solution Overview
Problem
Communication systems like the CAN bus in vehicles lack robust safety measures for authenticating messages, making them vulnerable to intrusions, where existing methods based on physical properties such as clock offsets or voltage signatures are either resource-intensive or can be circumvented by sophisticated intruders.
Innovation Solution
A method that determines the time difference between message reception points on a communication medium using a time-to-digital converter, forming a differential signal to cancel out electromagnetic interference, and dynamically setting a threshold value to accurately verify message authenticity, reducing the risk of incorrect time difference measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clock-based intrusion detection systems are used to identify message senders, then message authenticity can be verified, but aperiodic messages cannot be evaluated and intruders can circumvent the system by adapting to observed clock offsets
Solution Approach 1:
The patent changes the verification parameter from clock offset (time-based) to propagation time difference (spatial-based). By measuring the time difference of message arrival at two different positions on the communication medium, the system creates a new authentication parameter that is independent of the sender's clock and cannot be easily replicated by intruders, thus resolving the limitation with aperiodic messages and clock adaptation
2Measurement precision
If voltage signature analysis is used for intrusion detection, then detection accuracy is improved, but resource requirements increase due to comprehensive voltage signal analysis
Solution Approach 1:
The patent extracts only the essential timing information (propagation time difference) from the complex voltage signal analysis. Instead of performing comprehensive voltage signature analysis that requires significant computing resources, the system measures only the time difference of arrival at two positions, dramatically reducing computational requirements while maintaining authentication accuracy
Solution Approach 2:
The patent replaces the complex computational analysis of voltage signatures with a simpler time measurement approach. By substituting the resource-intensive voltage signal processing with straightforward time difference measurement, the system achieves comparable or superior detection accuracy with significantly reduced computing resources
3Reliability
If voltage-based intrusion detection is implemented, then authentication capability is provided, but the system becomes vulnerable to temperature-induced voltage fluctuations
Solution Approach 1:
The patent changes the authentication parameter from voltage-based to time-based measurement. By measuring propagation time difference instead of analyzing voltage signatures, the system eliminates vulnerability to temperature-induced voltage fluctuations, as time measurements are inherently more stable and less susceptible to environmental thermal variations
Data Source
AI summary
A method for checking a message in a communication system, in which multiple users are connected to a communication medium that includes two signal lines and exchange messages via same. A time difference between points in time of reception of a message that is sent on the communication medium is ascertained at two different, predefined positions on the communication medium, and based on a comparison of the time difference to at least one reference time difference, it is determined whether the message originates from a verified user. During the ascertainment of the time difference at the two positions, in each case a difference signal is formed from signals that have resulted on the two signal lines due to the message.