As technological advances allow GPS/GNSS devices to be more reliable, our lives are becoming increasingly dependent on accurate positioning and timing.
Today, GNSS time is used to synchronize telecom and energy grids, while precise positioning is used to navigate drones and self-driving cars, as well as to automate agricultural and construction machinery.
As new use cases pop-up on regular basis our reliance on GNSS grows globally. This means that having a secure spoof-proof communication channel between satellite and receiver becomes increasingly important to ensure trustworthy or Assured 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 anti-spoofing service, which allows secure end-to-end transmission from Galileo satellites to OSNMA-enabled GNSS receivers.
OSNMA (Open Service Navigation Message Authentication) will soon be available free of charge to users and has recently moved into the final testing phase.
As ESA’s long-term partner, Septentrio has been contributing to the design and testing of the Galileo system since its inception 20 years ago. Today Septentrio is playing a key role in the OSNMA testing efforts, with its receivers being the first to authenticate live OSNMA test signals.
OSNMA is one component of a vast array of technologies that protect GNSS receivers from interference. Both jamming and spoofing are a type of radio interference, which happen when weak GNSS signals are overpowered by stronger radio signals on the same frequency. Jamming is a kind of “white noise” interference, causing accuracy degradation or even loss of positioning.
Spoofing is a more sophisticated form of interference which fools a receiver into calculating a 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 fool a smartphone into showing its current location on top of Mount Everest!
OSNMA secures Galileo signals against spoofing by enabling authentication of navigation data, which carries information about satellite location. Navigation data security is important because any modification of this information would result in erroneous positioning calculation.
A sophisticated algorithm within the OSNMA-enabled receiver uses a public key to check the authenticity of the transmitted key. It then uses the transmitted key and the digital signature to check the authenticity of the navigation data. If a satellite signal is flagged as spoofed, it is excluded from the positioning calculation.
OSNMA is one piece of the puzzle comprising a sophisticated interference defense system, such as AIM+. For example, AIM+ can also detect spoofing by searching for signal anomalies, such as unusually high power. It also works together with RAIM+ integrity algorithm to ensure range (distance to satellite) validity by comparing ranging data from various satellites.