Galileo OSNMA adds a digital signature to Galileo navigation data so a receiver can check that the data really came from Galileo. That makes spoofing harder and easier to detect. EUSPA says plainly that it does not prevent spoofing or jamming, and it covers Galileo, not GPS.
What OSNMA is
OSNMA stands for Open Service Navigation Message Authentication. It is run by EUSPA, the EU agency for the space programme, and the service was launched officially on 24 July 2025. Galileo is described as the first satellite navigation system to offer this kind of authentication worldwide as part of its open service.
Before OSNMA, a civilian receiver had no cryptographic way to tell a real satellite message from a convincing fake. A spoofer only had to build a signal that looked right. With authentication, a fake that cannot produce a valid signature can be rejected or flagged.
How it works in practice
The cryptographic data rides in the I/NAV navigation message on the E1-B signal. It uses fields that were previously reserved, so the signal structure and open service performance do not change.
The receiver does the checking. It needs to implement the OSNMA protocol, and it must download certified public keys from the European GNSS Service Centre. EUSPA notes that users do not store or manage secret keys. That is the usual public key design: the satellite side signs, and everyone can verify.
What it does not cover
Three limits matter if you are deciding whether OSNMA is enough for your product.
- Jamming is untouched. A jammer drowns the signal, and no signature helps if the receiver hears nothing.
- It is not a spoofing block. Authentication lets a receiver notice and reject bad data. It does not stop someone from broadcasting it.
- It is Galileo only, for now. The EUSPA service page lists planned extensions, including F/NAV data, GPS L1 C/A navigation data, and a separate service aimed at protecting the signal at a deeper level. Those are plans, so check the current status before you design around them.
The service page also says OSNMA currently authenticates ephemeris and timing data on E1-B, and that end to end protection depends on the receiver following EUSPA's receiver guidelines.
Questions to ask a device maker
If you buy equipment that depends on satellite timing or position, ask whether the receiver supports OSNMA, whether it enforces the check or only logs it, and what the device does when authentication fails. A receiver that quietly keeps using unauthenticated data gives you little. Also ask what the fallback is when the signal is jammed, because authentication will not solve that case.
Where this fits in a wider plan
Treat OSNMA as one layer. Authenticated data helps against fake satellite messages. Other layers, such as a second time source, a holdover oscillator, or inertial sensors, help when the signal is jammed or disagrees with other sources. None of those layers is a substitute for the others.
Quick check
Does OSNMA work with GPS?
Not today. It authenticates Galileo open service data. EUSPA's service page lists GPS L1 C/A navigation data among the planned extensions, so ask your supplier about the current state.
Will an OSNMA receiver still fail under jamming?
Yes. EUSPA states OSNMA does not prevent jamming. A jammed receiver has no signal to authenticate.
Sources
- EUSPA: Galileo OSNMA
- EUSPA press release: Galileo to be the first GNSS to offer authentication service worldwide with launch of OSNMA
Last reviewed: 19 October 2026.
