So, in the ancient times I wrote a blog post on how to run a Tor bridge on a non privileged port (< 1024). Water flows, time flies, operating systems get updated and security increases. As a result, our good old howto is not valid anymore.
I found it the usually hard way: I upgraded my Tor Bridge server from Ubuntu14 to Ubuntu16 and obfs4proxy wasn’t able anymore to bind to port 80 and 443:
Tor[748]: Server managed proxy encountered a method error. (obfs3 listen tcp [::]:443: bind: permission denied)