Observer: How Galileo OSNMA helps counter GNSS spoofing

From finding our way with maps on our phones to synchronising banking transactions, satellite navigation is so deeply woven into daily life that we hardly notice it anymore. These signals are highly reliable, but attempts to interfere with or fake them, such as jamming and spoofing, are increasing. As our reliance on Global Satellite Navigation System (GNSS) technologies grows, measures which safeguard the integrity of positioning and timing signals become more important. Recognising this, the European Commission has introduced Galileo OSNMA, a free service which allows devices to verify that Galileo navigation messages are genuine. In this Observer, we explore how the new OSNMA service is strengthening navigation security. 

Everyday life depends on GNSS. Aircraft rely on them for landing approaches, ships to plan routes, and smartphones for everything from food delivery to emergency calls. Banking and energy sectors also rely on precise satellite timing to keep financial transactions and power grids running smoothly, with GNSS providing the trusted timestamps that underpin transaction authentication and grid synchronisation.

The more these signals become integrated into our daily lives, the more attractive they become as targets for malicious actors. Spoofing, in which fake signals are transmitted so GNSS receivers compute the wrong position or time, and jamming—the deliberate transmission of radio frequency interference which degrades or denies GNSS reception—are growing risks.  A spoofed signal can redirect ships or drones off course and feed false data into critical infrastructure. Jamming, on the other hand, can paralyse navigation systems at airports, disrupt logistics chains, and even compromise emergency services which depend on timing synchronisation.

In recent years, the number of spoofing and jamming cases has increased significantly, coinciding with Russia’s invasion of Ukraine. For example, Poland reported 2,732 cases in January 2025 (up from around 1,900 in October 2023), while Lithuania recorded over 1,000 incidents in a single month, which is 22 times more than in June 2024. Aviation reports also confirm regular interference affecting flights over the Baltic and Black Sea regions.

Spoofing and jamming devices are low-cost and highly accessible. Commercial off-the-shelf jammers and spoofers are widely available, meaning a sophisticated, multi-billion-euro GNSS can be disrupted or degraded by relatively cheap devices that anyone can buy.

This is where Galileo’s OSNMA comes in. It’s Europe’s first navigation authentication service, designed to give users a way to verify that the data they receive is genuine. While OSNMA specifically strengthens resilience against spoofing, it also complements broader security measures aimed at countering jamming, reinforcing the overall reliability of Europe’s navigation services.

What is OSNMA? 

OSNMA stands for Open Service Navigation Message Authentication. It is part of the Galileo Open Service, available to all users free of charge, and represents the first civil GNSS authentication capability in the world.

At its core, OSNMA works like a digital signature for standard Open Service navigation signals. Without authentication, a satellite message looks much like any other: easy to copy, rebroadcast, or manipulate. With OSNMA, however, each Galileo message carries a cryptographic signature proving its origin. 

Receivers that support OSNMA can verify that the signal genuinely comes from Galileo and reject counterfeit or replayed signals. For the first time, civil users can benefit from an operational navigation message authentication service, free of charge via Galileo OSNMA.

As GNSS navigation messages are broadcast at very low data rates, Galileo engineers tailored OSNMA to operate reliably in high-loss, low-data-rate environments. This allows authentication to succeed even if reception is intermittent, for example when some satellites are blocked by buildings or terrain. One key requirement is that receivers must be synchronised to Galileo System Time within a given accuracy so replayed data can be detected and rejected. With this in place, OSNMA is able to provide robust authentication of Galileo navigation messages under real-world conditions.

“With OSNMA, we increase assurance that the data users receive is indeed coming from Galileo and has not been modified in any way” 

- EUSPA Executive Director Rodrigo da Costa

Development and deployment timeline

The journey to OSNMA has been over a decade in the making, with OSNMA end-to-end design and proof of concept going back as early as 2013. Between 2016 and 2018, the feature was formally included in Galileo’s service baseline, with initial test specifications released. From 2019 to 2021, development accelerated within the European GNSS Service Centre, leading to the first continuous signal-in-space (SIS) transmissions and the launch of the OSNMA Public Observation Phase.

Refinements, operational validation, and accreditation followed between 2022 and 2025, culminating in the Initial Service Declaration on 24 July 2025. This was the moment Galileo officially became the first global navigation system to provide open authentication to its users. 

Why this is timely

What makes OSNMA such a milestone is not just the technology but what it represents: Europe leading the way in GNSS resilience. None of the other GNSS providers currently offer open authentication for civil users. Galileo fills this gap with a capability that is both a world-first and freely accessible.

The implications are wide-reaching. For finance, telecoms, and energy networks OSNMA boosts trust in timing signals which underpin transactions and synchronisation. In transport, whether aviation, shipping, or road logistics, it brings greater confidence that navigation data is genuine.

Importantly, OSNMA makes signals far harder to spoof. While data authentication does not eliminate all risks, by adding cryptographic unpredictability to Galileo’s messages and enabling receivers to apply cross-checks, it raises the barrier for attackers and strengthens trust in satellite navigation across the sectors which depend on it.

Applications across sectors

International aviation standards work has begun to incorporate OSNMA into the next generation of avionics. While in the automotive sector, OSNMA is already part of the second-generation smart tachograph, mandated across the EU under the Mobility Package, meaning trucks engaged in international transport will progressively adopt this authentication layer, paving the way for safer connected and eventually autonomous vehicles.

“OSNMA is already finding its way into critical sectors” 

-Christoph Kautz, Director for Space Policy, Satellite Navigation and Earth Observation, at DG DEFIS

Maritime can also benefit, with reduced risks of spoofing in busy shipping lanes. In the emerging world of autonomous systems, drones and self-driving cars are expected to be able to navigate with greater confidence in the signals that guide them. Critical infrastructure also stands to gain. As mentioned previously, authenticating Galileo messages supports the trusted timing signals used by energy grids and financial networks. For everyday users, the benefit is simple: greater confidence in the services powered by Galileo.

Next steps

The launch of Initial Service is only the beginning. Work is under way with receiver manufacturers, standardisation bodies, and regulated sectors to ensure OSNMA is implemented across applications. Documentation and receiver guidelines are available from the European GNSS Service Centre to support integration. Looking further ahead, improvements are already planned: in the next years the service will expand with new authentication messages and better performance, part of a wider roadmap which includes additional authentication services such as signal-level authentication (SAS) and integration with Galileo’s Public Regulated Service (PRS), alongside the Galileo Second Generation satellites. Together, these steps will further strengthen resilience and ensure Europe remains at the forefront of GNSS security.