Technically both techniques can be used for gps hacking. It also seems you can fake a gps signal altogether, because the public signal is not cryptographically

Technically both techniques can be used for gps hacking. It also seems you can fake a gps signal altogether, because the public signal is not cryptographically signed, which surprises me (the only thing that makes sense to me is that the gps protocol doesn't have room for adding a signature, so it'd be a breaking change to the protocol).