Welcome to part 3 of my series on OSNMA, the proposed Galileo Navigation Message Authentication protocol. This part can be read independently from part 1 and part 2, but it might be useful to read the introduction to part 1. This post attempts to explain GPS (GNSS) jamming and spoofing, so it might be a useful read even if you don’t care about Galileo or its authentication. As usual, I’ve been helped tremendously by Daniel Estévez & many other researchers and Galileo professionals, and again I am very greatful for all the links, corrections, suggestions and knowledge you provided.