Galileo OSNMA: The Latest in GNSS Anti-Spoofing Security

GNSS in orbit. Image credit: © ESA-Pierre Carril

Because technological advances allow GPS / GNSS[1] devices to be more reliable, our lives are becoming increasingly dependent on accurate positioning and synchronization. Today, GNSS time is used to synchronize telecommunications and energy networks, while precision positioning is used to navigate drones and self-propelled vehicles, as well as to automate agricultural and construction machinery. As new uses regularly pop up, our reliance on GNSS is growing worldwide. This means that the presence of a tamper-proof communication channel between the satellite and the receiver is becoming increasingly important to ensure reliability or Secure PNT (Positioning, navigation and time), especially in critical and industrial applications.

To further improve transmission reliability, the European GNSS system, Galileo, has developed the OSNMA spoofing service, which allows secure end-to-end transmission from Galileo satellites to GNSS receivers with OSNMA enabled. OSNMA (Open Service Navigation Message Authentication) will soon be available for free to users and has recently entered its final testing phase. As a longtime partner of ESA, Septentrio has contributed to the design and testing of the Galileo system since its inception 20 years ago. Today, Septentrio plays a key role in OSNMA testing efforts, with its receivers being the first to validate OSNMA test signals live.

Figure 1: During a counterfeit attack, the modified GPS / GNSS data is sent to the target receiver, deceiving them into the wrong location.

Protection of GNSS receivers against jamming and tampering
OSNMA is one of the components of a wide range of technologies that protect GNSS receivers from intervention. Attenuation and counterfeiting are a type of radio interference that occurs when weak GNSS signals are overcome by stronger radio signals at the same frequency. Silence is a type of “white noise” interference that causes a deterioration in accuracy or even a loss of positioning.

Forgery is a more complex form of interference that tricks the receiver into calculating the wrong location. During a spoofing attack, a nearby radio transmitter sends fake GNSS signals to the target receiver. For example, a cheap SDR (Software Defined Radio) can trick a smartphone into showing its current location on top of Mount Everest!

You may have caught some fake events presented in the latest news. For example, C4ADS, a non-governmental organization that analyzes conflicts and data issues, concluded that Russia makes extensive use of GNSS counterfeiting to deter air drones from entering airspace near government figures, airports and seaports. [2].

Figure 2: A cryptographic algorithm inside an OSNMA-enabled GNSS receiver authenticates Galileo OSNMA signals.

Highly secure protection against tampering with OSNMA
OSNMA provides Galileo anti-counterfeiting signals, allowing navigation data to be authenticated, which carries information about the satellite’s location. The protection of navigation data is important, as any change to this information would lead to an incorrect positioning calculation.

OSNMA uses a hybrid symmetric / asymmetric cryptographic technique. A secret satellite key is used to generate a digital signature. Then both the signature and the key are added to the navigation data and transmitted to the receiver. OSNMA is designed to be backward compatible, so positioning without OSNMA will continue to work.

Authentication with OSNMA enabled receivers
A sophisticated algorithm within the OSNMA-enabled receiver uses a public key to authenticate the transmitted key. It then uses the transmitted key and digital signature to verify the authenticity of the navigation data. If a satellite signal is marked as forged, it is excluded from the positioning calculation.

OSNMA is part of a puzzle involving a complex interference protection system, such as AIM + (see image below). For example, AIM + can also I discover forgery by looking for signal anomalies, such as unusually high power. He also works with RAIM + integrity algorithm to ensure the validity of the range (distance to the satellite) by comparing data from different satellites.

AIM + will not even be fooled by an advanced GNSS signal generator, ie. Spirent GSS9000. Even with realistic power levels and valid navigation data, AIM + still identifies the simulated signal as “non-authentic”.

Today, other advanced anti-counterfeiting techniques are being developed, such as the use of a double-polarized antenna, read more about this method here.

Figure 3: OSNMA is a piece of the puzzle that includes an advanced interference protection system: AIM + (Advanced Interference Mitigation), which protects the GNSS receiver against jamming and tampering.

Sustainable future receivers for today and tomorrow
OSNMA is already being implemented today to ensure synchronization of telecommunications networks in the GSA-led ROOT project, with Septentrio being a key partner. Within this project, mosaic-T The GNSS module, equipped with AIM + technology, provides a flexible and accurate solution for synchronizing critical infrastructure. Various global players such as Airbus were the first to test Galileo’s OSNMA live signal authentication with Septentrio GNSS dedicated receivers.

The US GPS system is also developing its own authentication mechanism called Chimera. Future-resistant GNSS receivers are designed to allow users to take advantage of OSNMA, Chimera and other GNSS value-added services as soon as they become publicly available. Integrating future-proof receivers into high-precision solutions allows companies to be the first in the market with products or services offering the latest in PNT sustainability.

[1] Global navigation satellite system, including the American GPS, the European Galileo, the Russian GLONASS, the Chinese BeiDou, the Japanese QZSS and the Indian NavIC. These satellite constellations transmit position information to receivers who use it to calculate their absolute position.

[2] Counterfeiting incidents are regularly reported in the news, read findings on recent fake attacks from C4ADS.

For more information on counterfeiting, see Insight What is counterfeiting and how to ensure the security of GNSS

Read more about ROOT a project that uses OSNMA for secure synchronization of telecommunications networks.

For the North
Septentrio designs and manufactures multi-frequency multi-constellation GPS / GNSS positioning technology for demanding applications. Reliable centimeter-level positioning allows machine automation to improve efficiency and safety. Septentrio offers positioning solutions for industrial applications such as robotics, construction, exploration and mapping, the marine industry, logistics and unmanned aerial vehicles (UAVs). Septentrio is headquartered in Leuven, Belgium and has a global presence with offices in Los Angeles, Shanghai, Seoul and Yokohama, as well as numerous partners around the world. To learn more about Septentrio and his products, visit

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