The vulnerability of the Global Positioning System (GPS) has been widely recognized. Radio frequency interference caused by interference and spoofing is used to reduce the performance of important synchronization systems that provide location, navigation and time information (PNT) for critical national infrastructure.
Most of this RF interference comes from electronic equipment, radio antennas or modems, which are strong enough to overwhelm the relatively weak signal sent to the GNSS (Global Navigation Satellite System) receiver. This vulnerability provides an attractive target for misconduct.
Radio expert U-Blox senior director of positioning technology Rod Bryant (Rod Bryant) said: “Bad guys are facing more and more threats, so we need to find ways to analyze and respond to them.
These protections range from the navigation message authentication and signal encryption of the European Galileo system to the GPS anti-spoofing framework with similar message authentication schemes.
Before we delve into these and other resilience methods, let’s take a look at the growing threat to GNSS and briefly review the impact of GPS interference over the past few years.
Interfering with GPS signals only needs to generate enough RF signals to drown out GNSS transmissions. Generally, small transmitters transmit radio signals in the same frequency band as GPS devices. The resulting interference can disrupt the reception on the GPS device.
gps jammer are indistinguishable and usually cause collateral damage. Air traffic control, search and rescue, power grids, and mobile phone services that rely on GPS are all vulnerable to GPS events.
Jammers only block GNSS signals, making precise positioning difficult or impossible, while GPS spoofing involves deliberate signal transmission similar to GPS but with incorrect location information. By copying the GNSS signal, a spoofer can mislead the receiver that it is at a specific point in time or at a different location.
Deception will cause all kinds of chaos. For example, it can be used to hijack self-driving cars and send them on alternate routes. Spoofing may change the route recorded by the vehicle monitor or destroy the geofence used to protect the operating area. It also poses risks to critical infrastructure including power, telecommunications and transportation systems.
Jan van Hees, director of business development and marketing at Septentrio, a GNSS receiver manufacturer, provides the following analogy: “When interference is encountered, a lot of noise is generated, so that [satellite signal] disappears. Deception is like a phishing attack on the signal.”
GPS interference is increasing
The U.S. Coast Guard has recently been tracking more and more incidents of GPS failure. For example, the loss of GPS receiving equipment at Israeli ports in 2019 made GPS-controlled automatic cranes unusable, which was collateral damage caused by the Syrian civil war. In 2016, more than 20 ships near the Crimea peninsula were believed to be victims of GPS spoofing attacks that changed the ship’s position on the electronic chart display.
GNSS interference caused the US Department of Transportation’s Maritime Administration to issue a GPS interference warning last year. The information to the industry emphasizes the necessity of using alternative PNT systems. The agency was concerned about complacency and emphasized the sources of interference, including multipath, atmospheric conditions, and GNSS segment issues, such as incorrect data uploads.
Since 2018, GNSS interference incidents by European aviation authority Eurocontrol have increased by 2,000% after a GPS accident in Norway (which may have originated in nearby Russia). A report also emphasized that RFI interference is disproportionate: Although most RFI hotspots are in conflict areas, they also affect civil aviation within 300 kilometers, indicating that interference has caused excessive lethality.
In another case, GPS jammers are used to hide the location of stolen luxury cars and fully loaded shipping containers. According to Guy Buesnel, a GNSS vulnerability expert at Spirent Communications, the FBI issued an announcement in 2014.
Buesnel highlighted the government’s efforts to raise awareness of GNSS vulnerabilities. For example, a report estimated that in five days, the total loss of GNSS would have an economic impact of 5.2 billion pounds in the UK.
These and parallel efforts by the United States have led to efforts to improve the resilience of the GNSS system. Van Hees of Septentrio said: “Accuracy is important, but confidence in the system is important. We need reliability and availability.” “For example, can you receive signals under adverse conditions?”
Trust also requires steps such as signal fingerprinting to distinguish spoofers from satellite signals. For example, the signal strength and timing from the spoofer may be useless, especially because the signal strength of satellite broadcasts is low. Signal encryption is another option, including a framework called Open Service Navigation Message Authentication (OSNMA).
Spirent’s Buesnel emphasized the necessity of auditing and risk assessment as an important part of PNT’s security, resilience and robustness. He said: “Testing to quantitatively understand how the existing system responds to real-world threats and evaluating the proposed mitigation measures is an integral part of it.” “Unexpected behavior or consequences are usually lack of implementation before the system is deployed. The result of comprehensive testing and risk assessment.”
The OSNMA anti-spoofing service developed for European GNSS systems enables secure transmission from Galileo satellites to encrypted GNSS receivers. During the final test period, OSNMA will soon be available to users for free.
OSNMA protects Galileo signals by enabling authentication of navigation data containing satellite position data. It uses hybrid symmetric/asymmetric encryption technology. The key on the satellite is used to create the digital signature. Both the signature and the key are attached to the navigation data and sent to the recipient. OSNMA is backward compatible, so you can continue positioning without OSNMA.
The European GNSS agency stated that it will use the replacement bits in the current navigation message to send the OSNMA test signal from the Galileo constellation without affecting the older open services. The first test last November included eight Galileo satellites. Testing will continue in the next few months.
Septentrio said its receiver verified navigation data from the first OSNMA-encrypted GNSS satellite signal. Even the security authentication through OSNMA has potential flaws. U-Blox’s Kobe said: “OSNMA has security flaws in the way it provides keys.” “If you are a smart cheater, you can delay the signal to get the key.” Nevertheless, Kobe still believes that OSNMA is in Europe for a certain Some applications may become mandatory.
He also believes that the GPS authentication system can potentially overcome this vulnerability. The proposed mosaic system for protecting GPS signals inserts encrypted digital signatures and watermarks into satellite signals. The signal authentication enhancement function can jointly authenticate the navigation data and propagation codes of civil GPS signals.
Chimera uses the concept of time limitation, where the extension code is interrupted by markers that are cryptographically generated using a key derived from a digitally signed navigation message. Navigation messages and distribution codes cannot be generated independently of each other. Bit promises ensure that spoofers can only generate correct tokens after broadcasting.
Two variants are given: a “slow” channel for independent users and a “fast” channel when out-of-band information is available for faster authentication. In the latter case, binding is achieved by delaying the disclosure of the cryptographic key.
NIST, DHS case
Earlier this year, the National Institute of Standards and Technology (NIST) issued an authoritative cybersecurity guide for PNT services. The guidelines consider the network security risks of PNT and GPS services, as well as their impact on national and economic security.
NIST’s Jim McCarthy (Jim McCarthy) said: “Before the development of this profile, a lot of efforts have been made to ensure the security of the PNT service, but there is no official reference material that can mitigate the risk that anyone can use.”
United States. The Science and Technology Bureau of the Department of Homeland Security (DHS) also allocated resources earlier this year to protect critical infrastructure from GPS spoofing. These free tools include the PNT integrity library and the Epsilon algorithm suite, both of which are designed to increase the flexibility of PNT.
“The increasing reliance on GPS for military, civilian, and commercial applications has increased the vulnerability of PNT systems that verify or authenticate ranging signals according to the Space Policy 7 released in January, especially in those that may cause even minor degradation. Application of death,” the policy warns. .
The PNT integrity library and the Epsilon algorithm suite solve this problem by providing users with a way to verify the integrity of the received GPS data. Brannan Villee said the new tool will help “improve resilience against potential GPS signal loss.” PNT program manager at DHS.
Jim Platt, Director of the National Risk Strategic Defense Program of the Cybersecurity and Information Security Agency, added: “Since GPS signals may be interfered with or forged, one should not assume that GPS data is always available or accurate. Design key infrastructure systems under the management center.
“Using these tools can improve security against GPS jammers. However, DHS also recommends an overall defense strategy that should consider the integrity of the PNT data used in the supported system from the time it is received,” Platt said.
GNSS signals are getting more and more fragile, and flexible work continues to affect the threat of interference and deception. The OSNMA architecture is very advanced in testing and will soon be popularized in Europe. The GPS chimera specification is still in the early stages of testing. In the end, the experts agreed that the security of GNSS signals must be fully considered and many factors including signal diversity, fingerprint recognition and encryption must be considered. Only in this way can the output of the PNT system be trusted.