Passive remote keyless entry system with level-based anti-theft feature
Method for preventing security breaches via the two-thief method of attack of passive remote keyless entry systems for vehicles. The method involves the transmission of a signal between a fob and the vehicle, where the level of the signal changes in a particular pattern. At the receiving side, anomalies in the pattern of the received signal (e.g., levels, timing) are detected and used to detect attempts to mimic the signal.
1. A method for preventing security breaches of passive remote keyless entry systems for a vehicle comprising:
transmitting an inquiry signal from a remote keyless entry controller associated with the vehicle to a fob when a door handle contact is detected;
receiving the inquiry signal at the fob;
transmitting an inquiry signal response from the fob to the remote keyless entry controller that contains a fob identifier;
receiving the inquiry signal response at the remote keyless entry controller;
determining, at the remote keyless entry controller, if the received inquiry signal response containing the fob identifier is valid;
when the remote keyless entry controller determines that the received inquiry signal response containing the fob identifier is valid, transmitting broadcast instructions from the remote keyless entry controller at the vehicle to the fob, the broadcast instructions including a particular sequence of power level changes for a response signal from the fob to follow;
receiving the broadcast instructions at the fob;
transmitting the response signal from the fob to the remote keyless entry controller at the vehicle at the power level which changes in the particular sequence received in the broadcast instructions; and
receiving the response signal at the remote keyless entry controller at the vehicle;
detecting, with the remote keyless entry controller, anomalies in the particular sequence of the response signal by:
1) comparing detected absolute signal amplitudes in the particular sequence of the response signal to corresponding predetermined absolute signal amplitude ranges stored in the vehicle to determine incorrect absolute amplitudes in the particular sequence; and
2) detecting incorrect relative signal amplitudes in the particular sequence.
2. The method as set forth in claim 1 , wherein the transmitting the response signal from said fob comprises transmitting in the particular sequence that includes high level and low level transmissions, the method further comprising:
receiving the response signal at a receiver connected to the remote keyless entry controller, wherein the receiver is configured with a first gain and/or bandwidth to receive the high level transmission and the receiver is configured with a second gain and/or bandwidth to receive the low level transmission.
3. The method as set forth in claim 1 , wherein the detecting anomalies comprises detecting incorrect time delays in said particular sequence.
4. The method as set forth in claim 1 , wherein the detecting anomalies further comprises detecting incorrect frequency content of said particular sequence.
5. The method as set forth in claim 1 , wherein the detecting anomalies further comprises detecting incorrect ASK/FSK modulation of said particular sequence.
6. The method as set forth in claim 1 , and further comprising changing said particular sequence each time said fob and said vehicle communicate.
7. The method as set forth in claim 1 , and further comprising performing a vehicle function only if there are no unexpected anomalies in said particular sequence of said response signal.
8. The method as set forth in claim 1 , wherein said response signal has data modulated thereon and wherein said transmitting comprises transmitting at a level which changes at a rate that is slower than the rate of said data.
9. The method as set forth in claim 1 , wherein said predetermined sequence is encrypted.
10. The method as set forth in claim 1 , wherein the transmitting the response signal from the fob to the remote keyless entry controller at the vehicle comprises transmitting the response signal having different amplitudes in different amplitude signal intervals, each different amplitude in the particular sequence being detected and separately compared to a corresponding predetermined absolute signal amplitude range stored in the vehicle to determine incorrect absolute amplitudes in the particular sequence.
11. The method as set forth in claim 1 , further comprising disallowing access to the vehicle when the detected absolute signal amplitude falls outside the corresponding predetermined absolute signal amplitude range for a first time.
12. A method for preventing security breaches of a passive remote keyless entry system for a vehicle comprising:
transmitting an inquiry signal from a remote keyless entry controller associated with the vehicle to a fob when door handle contact is detected;
receiving the inquiry signal at the fob;
transmitting an inquiry signal response from the fob to the remote keyless entry controller that contains a fob identifier;
receiving the inquiry signal response at the remote keyless entry controller;
determining, at the remote keyless entry controller, if the received inquiry signal response containing the fob identifier is valid;
when the remote keyless entry controller determines that the received inquiry signal response containing the fob identifier is valid, transmitting broadcast instructions from the remote keyless entry controller at the vehicle to the fob, the broadcast instructions including a particular sequence of power level changes for a response signal from the fob to follow;
receiving the broadcast instructions at the fob;
transmitting the response signal from the fob to the remote keyless entry controller at the vehicle at the power level which changes in the particular sequence received in the broadcast instructions;
receiving the response signal at the remote keyless entry controller at the vehicle;
detecting, with the remote keyless entry controller, deviations of the received response signal from the particular sequence by:
1) comparing detected absolute signal amplitudes in the sequence to corresponding predetermined absolute signal amplitude ranges stored in the vehicle to determine incorrect absolute amplitudes in the sequence, and
2) detecting incorrect relative signal amplitudes in the sequence; and
performing a vehicle function only if the deviations are within acceptable limits.
13. The method as set forth in claim 12 , and further comprising changing said particular sequence each time said fob and said vehicle communicate.
14. The method as set forth in claim 12 , wherein said response signal has data modulated thereon and wherein said transmitting the response signal comprises transmitting at a level which changes at a rate that is slower than the rate of said data.
15. The method as set forth in claim 12 , wherein the performing the vehicle function comprises unlocking a vehicle door to allow entry into the vehicle.
16. The method as set forth in claim 12 , wherein the performing the vehicle function comprises starting the vehicle.
17. The method as set forth in claim 12 , wherein the transmitting the response signal from the fob to the remote keyless entry controller at the vehicle comprises the transmitting the response signal having different amplitudes in different amplitude signal intervals, each different amplitude in the particular sequence being detected and separately compared to a corresponding predetermined absolute signal amplitude range stored in the vehicle to determine incorrect absolute amplitudes in the particular sequence.
18. The method as set forth in claim 12 , further comprising disallowing access to the vehicle when the detected absolute signal amplitude falls outside the corresponding predetermined absolute signal amplitude range for a first time.