> Galileo was the ugly duckling for a very long time - but it turned into a shining one after it aged a bit.

Yeah, for some time I was also in the camp of "why we need our own expansive service". But the current development has shown, that it was a wise desicion to have our own system.

BTW: thanks for updating on some other details. I never followed up really, it was from the initial plans, that I was told there should be comercial service, that should pay. Also that for some emergency services there is a very limited possibility to have a back channel.

As far as I know all nav sats have emergency beacon payloads (Cospas-Sarsat). All providers (Beidou, GPS, Glonass, Galileo) joined this.

It has optional cryptographic signatures of the navigation message, i.e. the data indicating position of satellites.

Spoofing generally works not by altering the navigation message, but by altering the timing of arriving signals. I'd recommend this video for a publicly-available overview of the techniques: https://www.youtube.com/watch?v=sAjWJbZOq6I

tl;dr Galileo spoofers exist and work just fine.

Nope, the GNAV message is not only the position of the sateellites, the almanac https://gssc.esa.int/navipedia/index.php?title=Galileo_Navig...

Spoofing of Galileo was possible as long as the authentification was not enabled. https://www.septentrio.com/en/learn-more/insights/osnma-late...

In other comments to this link people are describing GPS according to my mental model, which is hard to combine with cryptography making it un-spoofable.

If someone can re-broadcast the keystream and control the latency I perceive as a receiver, how would me checking that the MAC is correct help?

A) you keep on using the word "almanac". That term only refers to the imprecise information about all satellites that every satellite broadcasts, mostly to improve TTFF. The actual position used for navigation is called "ephemeris", and each satellite only broadcasts its own.

B) none of that other stuff in the navigation message changes the pseudorange, which is what spoofers mess with. For a networking analogy - pseudoranges are calculated based on layer 1/2 properties of the network. (Specifically the code phase and Doppler shift.) Navigation messages are layer 7 information passed on top of that physical layer. You can change the timing and frequency characteristics of the PRN code without touching a single bit of the navigation message.)

The G/NAV message (note the G - government) is for a separate service - not OSNMA - where not only is the navigation message encrypted, but the PRN code is also encrypted (symmetrically, so it can't be done for the mass market or even untrusted commercial customers).