New GNSS anti-spoofing service developed

Wednesday, 21 April, 2021

New GNSS anti-spoofing service developed

As our lives become increasingly dependent on GPS/GNSS devices, it becomes increasingly important to have a secure, spoof-proof communication channel between satellite and receiver to ensure trustworthy or assured PNT (positioning, navigation and time), especially in critical and industrial applications. To improve transmission reliability, European GNSS system Galileo has developed the OSNMA (Open Service Navigation Message Authentication) anti-spoofing service, which allows secure end-to-end transmission from Galileo satellites to OSNMA-enabled GNSS receivers.

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, using a nearby radio transmitter to send fake GNSS signals to the target receiver.

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.

OSNMA makes use of a hybrid symmetric/asymmetric cryptography technique. A secret key on the satellite is used to generate a digital signature, then both signature and key are appended to the navigation data and transmitted to the receiver. 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 just one piece of the puzzle comprising a sophisticated interference defence system, such as AIM+. 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. AIM+ won’t even be fooled by an advanced GNSS signal generator such as Spirent GSS9000. Even with realistic power levels and valid navigation data, AIM+ still identifies the simulated signal as ‘not authentic’.

OSNMA will soon be available free of charge to users and has now moved into the final testing phase, with GNSS technology manufacturer Septentrio using its receivers to authenticate live OSNMA test signals. OSNMA is also being implemented to secure synchronisation of telecom networks in the GSA-led ROOT project, with Septentrio as a key partner. In the framework of this project, the mosaic-T GNSS module, equipped with AIM+ technology, provides a resilient timing solution to mission-critical infrastructure. Various global players, such as Airbus, will be the first to try out OSNMA authentication of live Galileo signals with specialised Septentrio GNSS receivers.

Image credit: ©ESA-Pierre Carril

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