Three examples of this, implemented and working:

- https://www.sharedrop.io/ - https://www.justbeamit.com/ - https://file.pizza/

Ongoing work is happening, for example by the webtorrent folks, to remove this constraint.

Do these services also act as connectors in case of double NAT?

Would that meet the requirements without being a "central" service?

Just take any .onion domain and append it with .to and it should work. examplelettersblah.onion becomes examplelettersblah.onion.to and that works without needing to muck about with Tor.

This would be a horrible idea if you're concerned with privacy/anonymity. But, it'd make it easy for people to download your shared files.

then you're clearly not the person we should be asking to build this kind of thing are you? :-)

my proposal actually solves two important problems with peer-to-peer systems, and I barely have to write any new code to make it work! the solution? i2p! it's an anonymous mix network, much like Tor, but completely decentralized. using an intermediary dex mix network fixes the nat issue and prevents you from leaking your IP address to other peers.

https://geti2p.net/en/comparison/tor

(Serious question - I've not used it myself, and I'm intrigued at the process.)

endpoints are identified by their public key hash. each endpoint maintains a set of anonymized routes. this routing information is stored in a Distributed Hash Table (DHT). if you want to connect to another endpoint, you lookup the route for the public key hash, build an outbound route, and you're good.

more concretely, an ipfs transfer would work by using public key hashes in place of IP addresses to identify peers and a known set of endpoint keys for bootstrapping.

I like it.

Now, is it available today in a form (as the OP put it) which "A person whose computer knowledge extends to using facebook" can use?

https://geti2p.net/en/download

Am I missing something?

1. click bit torrent 2. click create torrent 3. type the path to your file 4. share magnet link

magnet:?xt=urn:btih:d0da0a2cac2bb3fd7ba6548edef12a24122ef481&tr=http://diftracker.i2p/announce.php

http://www.bittorrent.org/beps/bep_0005.html

- IPv6 kind of helps here, at least if we hope that no NAT standard ever makes it into IPv6. Crossing my fingers.

- There does exist at least one NAT hole-punching technique that can traverse two NATs with no central server using ICMP-based holepunching and UDP. Obviously, like all hole punching techniques, it only works on certain kinds of NATs, and firewalls can kill it.

I think you're referring to this? Clever hack indeed. https://github.com/samyk/pwnat

The fact that it doesn't support NAT is seen as a risk in such environments ( which rightly or wrongly consider it as a second level of firewalling ). Some deployments that I've seen use only site-scoped with no globally-routed prefixes. Everything Internetty has to go over IPv4, which makes the Security team's job easier; drop all IPv6 at the DMZ and drop all non-NAT IPv4.

I think the GNUnet has some stuff in it which can even work across different protocols, e.g. hopping across TCP/IP over Ethernet to Bluetooth to packet radio. It has some neat stuff where, as I recall, it probes out a random path, then tries to get at its intended destination, remembering successful attempts. It definitely sounds cool, but it's not currently in an end-user-usable state.

> I'm not aware of any entirely decentralised system [...]

What's the user value of having something entirely decentralized? I see the value in making sure the actual file transfer doesn't go through the central rendezvous. But I don't understand what's gained by eliminating the use of a little help setting up the connection.