Protected positioning, navigation, or timing signals resistant to spoofing
Positioning, navigation, and timing (“PNT”) signals, such as those used in GNSS or LORAN systems, may be vulnerable to spoofing attacks. To generate trustworthy time and location data at a receiver, one must at least reduce the likelihood of or be capable of detecting spoofing attacks. Embodiments of the present invention, as presented herein, provide solutions for detecting spoofing of PNT signals. Various aspects incorporated into the described embodiments which assist in detecting spoofing attacks may include but are not limited to: monitoring the SNR of received PNT signals of a first modality and switching over to an alternate PNT modality when an anomaly is detected, comparing data associated with signals of multiple PNT modalities to identify a discrepancy indicative of spoofing on one of the multiple PNT modalities, and implementing a security regime to prevent spoofers from being able to produce perceivably authentic, but corrupt, replica signals of a PNT modality.
1. A method for verifying authenticity of radio navigation signals, comprising:
storing, at a secure receiver, information regarding a pseudo-random offset timing regime comprising a covert offset time, wherein the covert offset time corresponds to a delay between transmission of a first open radio navigation signal and transmission of a first closed radio navigation signal;
transmitting the first open radio navigation signal and the first closed radio navigation signal from a LORAN transmitter chain utilizing the covert offset time;
receiving, at the secure receiver, a first received open radio navigation signal.
2. The method of claim 1 , further comprising:
receiving, at the secure receiver, a first received closed radio navigation signal;
calculating a received offset time comprising a relationship between a time of receipt of the first received open radio navigation signal and a time of receipt of the first received closed radio navigation signal; and
comparing the received offset time with the covert offset time to determine authenticity of the first received open radio navigation signal.
3. The method of claim 2 , further comprising:
determining from the comparing that a PNT signal comprising the first received open radio navigation signal and first received closed radio navigation signal is authentic as a function of the covert offset time corresponding to the received offset time.
4. The method of claim 3 , wherein the first received closed radio navigation signal conveys data to the secure receiver useful for calculating at least one of position, navigation, or time.
5. The method of claim 4 , further comprising:
encrypting, at a transmitter, the pseudo-random offset timing regime; and
decrypting, at the secure receiver, the pseudo-random offset timing regime.
6. The method of claim 5 , wherein the pseudo-random offset timing regime further comprises a second offset time which is different than the first offset time and corresponds to a delay between transmission of a second open radio navigation signal and transmission of a second closed radio navigation signal; and
the method further comprises:
receiving, at the secure receiver, a second received open radio navigation signal and second received closed radio navigation signal;
calculating a second received offset time corresponding to reception of the second received open radio navigation signal and reception of the second received closed radio navigation signal; and
comparing the second offset time to the second received offset time.
7. The method of claim 1 , further comprising:
determining that a PNT signal comprising the first received open radio navigation signal is spoofed based on the PNT signal being deficient of a closed radio navigation signal.
8. The method of claim 7 , further comprising:
entering a holdover mode in which a local clock is maintained in accordance with a time calculated prior to receipt of the first received open radio navigation signal.
9. The method of claim 1 , wherein the pseudo-random offset timing regime is received at the secure receiver via a secondary channel which is different than a radio communication channel on which open radio navigation signals or closed radio navigation signals are transmitted, wherein the secondary channel is an internet-accessible wired or wireless network connection.