Vehicle Passive Access Relay Attack Detection
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Solution Overview
Problem
Existing passive access systems in motor vehicles are vulnerable to relay attacks, which allow unauthorized individuals to trigger vehicle functions by extending the radio signal path between the ID transmitter and the vehicle, making it difficult to prevent unauthorized access.
Innovation Solution
A method involving a motor vehicle-side control unit coupled with two HF transmitting and receiving stations, along with an ID transmitter, performs an authentication process by comparing signal attenuations in both directions to detect any relay station interference, ensuring that the signal weakening on the vehicle side matches the signal weakening on the ID transmitter side, thus preventing relay attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If minimum transmission power is used as a security feature, then unauthorized triggering is prevented when operator is in vicinity, but relay attacks can circumvent this by extending the radio path
Solution Approach 1:
The system measures the received signal strength indicator (RSSI) of HF signals exchanged between the vehicle and ID transmitter, compares the measured RSSI values against expected ranges, and uses this feedback to detect anomalies indicating relay attacks. The control unit continuously monitors signal strength feedback to authenticate the proximity of the ID transmitter.
Solution Approach 2:
The patent replaces physical proximity verification with electromagnetic field-based RSSI measurement and comparison. Instead of relying solely on minimum transmission power constraints, the system uses HF signal strength measurements and spatial relationship analysis to detect relay attacks, substituting mechanical/security constraints with field-based detection.
2Difficulty of detecting and measuring
If HF signals are transmitted with predetermined transmission signal strength, then signal attenuation can be compared to detect relay stations, but this requires bidirectional signal exchange and measurement infrastructure
Solution Approach 1:
The HF transmitting and receiving stations serve multiple functions: they transmit authentication signals, measure received signal strength indicators, and provide spatial positioning information. The same HF communication infrastructure used for passive access authentication is also used for relay attack detection, eliminating the need for separate detection hardware.
Solution Approach 2:
The system uses its own HF communication signals to detect relay attacks. The same transmitting and receiving stations that facilitate normal passive access operations also perform the detection function by measuring signal attenuation and comparing spatial relationships, making the system self-sufficient without external detection equipment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly enhances security against relay attacks by ensuring that the signal path is spatially symmetrical, making it harder for a relay station to be positioned undetected, thereby preventing unauthorized function triggering.
Implementation Method 1
HF (radio frequency) transmitting and receiving station... HF signal from the motor vehicle is transmitted with a predetermined transmission signal strength
Implementation Method 2
The signal attenuation of the HF signal on the motor vehicle side is compared with the signal attenuation of the HF signal on the ID transmitter side
Data Source
Figure 1a~1b
Figure 2a~2b
AI summary
The invention relates to a method for triggering a function of a motor vehicle (1) by means of a passive access system, having a first HF transmitting and receiving station (3) and a second HF transmitting and receiving station (4), which are arranged on the motor vehicle (1) spaced apart from one another. The method comprises an authentication process, which is carried out for each of the first HF transmitting and receiving station (3) and the second HF transmitting and receiving station (4). The authentication process comprises: sending an HF-signal (8, 8') on the motor-vehicle side, sending an HF signal (9, 9') on the ID-transmitter-side, and comparing a signal attenuation of the HF-signal (8, 8') on the motor-vehicle side with the signal attenuation of the corresponding HF-signal (9, 9') on the ID-transmitter side.