SFTP-based VPN bootstrapping with automatic collision-free IPs assignment/peers' public data sharing

[Jason A. Donenfeld]

Hi ST,

It's a cool idea using the file system like that (the sticky bit would
make the permissions part work correctly, perhaps), though I wonder if
it's a bit complicated. If the model you're after is simply "server
allocates IPs for peers already known through some channel but with
unknown wireguard public keys", then maybe a better SSH-based
interface is a special user that is only allowed to run one program,
and that program does one thing: accepts as input a public key, and
outputs [without races] an allocated IP, endpoint, and the server's
public key. Under the hood that information could be stored in a
variety of ways. Alternatively, this could be its own protocol over
the wire or over TLS or over whatever the pre-established trust
mechanism is that the idea is based on. One of the earliest dirty bash
scripts for WireGuard did this (insecurely) over TCP --
https://git.zx2c4.com/WireGuard/tree/contrib/examples/ncat-client-server/server.sh
-- this is what's running on demo.wireguard.com.

Jason