433.92 ISM is only EU/Africa. So yeah in the US it would be illegal to use encryption. There are quite a few lower frequency ISM bands that might offer much greater range.

I'm interested in this stuff because I just started playing with these: https://cdn.sparkfun.com/assets/a/a/0/b/5/DS_SX1276-7-8-9_W_...

They do spread spectrum on ISM bands with extremely low data rates for insane sensitivity. I want to see what kind of stable distance you can get with lower frequencies and possibly even lower bitrates.