Inside GNSS Media & Research

MAY-JUN 2018

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www.insidegnss.com M A Y / J U N E 2 0 1 8 Inside GNSS 51 RINEX 3.02 for post-processing. e pseudorange and carrier phase were loaded from the RINEX file and code-carrier differ- ence was formed for the GPS L1 C/A signals. ese are plotted in Figure 5 for the first 20 minutes of the test for eight of the satellites observed. As can be seen, the code and carrier are coherent and do not diverge with time. As such, provided the spoofing hardware is appropriately configured (and regardless of whether it is low-cost or expensive) it is unlikely that it is possible to effect any level of spoofing detection based on the code-carrier coherency. Inconsistent navigation data is simultaneously a very good and very bad way to isolate a spoofed signal from a real one. In one sense it is an effective approach for a user with mul- tiple sources of information and who can, at the very least, flag navigation data inconsistencies as deserving of a closer look. In another sense it can be viewed as a weak approach, given that an adversary might generate any arbitrary navigation message, and might take relatively simple steps to ensure that the naviga- tion data carried by the counterfeit signals matches that which would be expected. at said, given the results of the unintentional spoofing at ION GNSS+ 2017, it appears that even when a consumer device has access to three or more streams of location and timing data (GNSS, LTE, WiFi), many implementations will happily travel three years back in time if their GNSS radio says to — implying that although the capability to detect message inconsistency is present in these devices, it is not necessarily exploited. While this aspect of spoofing resistance can certainly be improved, it might not be advisable to view it as robust against a moder- ately well prepared adversary who, for example, also might have an internet connection. Looking forward, even cryptographic message content that the attacker cannot generate can appear to be predicted given a small delay, and a clever attacker might find a way to insert one. It is not the case that we are adopting a new technology (GNSS), and doing so in full knowledge of the calculated risks — rather, we find ourselves having already fully embraced this technology, and only now are the risks coming to light. Delivering Aviation Approved GPS Solutions…Worldwide. www.aspennexnav.com Copyright 2017 Aspen Avionics Inc. "Aspen Avionics," "NexNav", "MAX," "Micro-i," and the Aspen Avionics aircraft logo are trademarks of Aspen Avionics Inc. All rights reserved. U.S. Patent No. 8,085,168, and additional patents pending. Approved NexNav ™ GPS solutions for the aerospace industry have a well-proven track record in civil and military, manned and unmanned applications. • GPS-SBAS circuit card assemblies and GPSSUs • Small size, lightweight and low power consumption • Approved for ADS-B OUT position source • Approved for enroute, terminal and approach GPS navigation • Products meet all expected GPS requirements for UAS BVLOS operations • Made in U.S.A. • Go to www.aspennexnav.com for more information Compact Size • Small size, lightweight and low power consumption • Approved for ADS-B OUT position source • Approved for enroute, terminal and approach GPS navigation • Products meet all expected GPS requirements for UAS BVLOS operations

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