In one of the good parts of the very mixed bag that is "Lo and Behold: Reveries of the Connected World", Werner Herzog asks his interviewees what the Internet might dream of, if it could dream.
The best answer he gets is along the lines of: The Internet of before dreamed a dream of the World Wide Web. It dreamed some nodes were servers, and some were clients. And that dream became current reality, because that's the essence of the Internet.
Three years ago, it seemed like perhaps another dream was developing post-Snowden, of dissolving the distinction between clients and servers, connecting peer-to-peer using addresses that are also cryptographic public keys, so authentication and encryption and authorization are built in.
Telehash is one hopeful attempt at this, others include snow, cjdns, i2p, etc. So far, none of them seem to have developed into a widely used network, although any of them still might get there. There are a lot of technical challenges due to the current Internet dream/nightmare, where the peers on the edges have multiple barriers to connecting to other peers.
But, one project has developed something similar to the new dream, almost as a side effect of its main goals: Tor's onion services.
I'd wanted to use such a thing in git-annex, for peer-to-peer sharing and syncing of git-annex repositories. On November 13th, I started building it, using Tor, and I'm releasing it concurrently with this blog post.
git-annex's Tor support replaces its old hack of tunneling git protocol over XMPP. That hack was unreliable (it needed a TCP on top of XMPP layer) but worse, the XMPP server could see all the data being transferred. And, there are fewer large XMPP servers these days, so fewer users could use it at all. If you were using XMPP with git-annex, you'll need to switch to either Tor or a server accessed via ssh.
Now git-annex can serve a repository as a Tor onion service, and that can
then be accessed as a git remote, using an url like
tor-annex::tungqmfb62z3qirc.onion:42913. All the regular git, and
git-annex commands, can be used with such a remote.
Tor has a lot of goals for protecting anonymity and privacy. But the important things for this project are just that it has end-to-end encryption, with addresses that are public keys, and allows P2P connections. Building an anonymous file exchange on top of Tor is not my goal -- if you want that, you probably don't want to be exchanging git histories that record every edit to the file and expose your real name by default.
Building this was not without its difficulties. Tor onion services were originally intended to run hidden websites, not to connect peers to peers, and this kind of shows..
Tor does not cater to end users setting up lots of Onion services.
Either root has to edit the
torrc file, or the Tor control port can be
used to ask it to set one up. But, the control port is not enabled by
default, so you still need to su to root to enable it. Also, it's difficult
to find a place to put the hidden service's unix socket file that's
writable by a non-root user. So I had to code around this, with a
annex enable-tor that su's to root and sets it all up for you.
One interesting detail about the implementation of the P2P protocol in git-annex is that it uses two Free monads to build up actions. There's a Net monad which can be used to send and receive protocol messages, and a Local monad which allows only the necessary modifications to files on disk. Interpreters for Free monad actions can chose exactly which actions to allow for security reasons.
For example, before a peer has authenticated, the P2P protocol is being run by an interpreter that refuses to run any Local actions whatsoever. Other interpreters for the Net monad could be used to support other network transports than Tor.
When two peers are connected over Tor, one knows it's talking to the owner of a particular onion address, but the other peer knows nothing about who's talking to it, by design. This makes authentication harder than it would be in a P2P system with a design like Telehash. So git-annex does its own authentication on top of Tor.
With authentication, users would need to exchange absurdly long addresses (over 150 characters) to connect their repositories. One very convenient thing about using XMPP was that a user would have connections to their friend's accounts, so it was easy to share with them. Exchanging long addresses is too hard.
This is where Magic Wormhole saved the day. It's a very elegant way to get any two peers in touch with each other, and the users only have to exchange a short code phrase, like "2-mango-delight", which can only be used once. Magic Wormhole makes some security tradeoffs for this simplicity. It's got vulnerabilities to DOS attacks, and its MITM resistance could be improved. But I'm lucky it came along just in time.
So, it takes only installing Tor and Magic Wormhole, running two git-annex commands, and exchanging short code phrases with a friend, perhaps over the phone or in an encrypted email, to get your git-annex repositories connected and syncing over Tor. See the documentation for details. Also, the git-annex webapp allows setting the same thing up point-and-click style.
The Tor project blog has throughout December been featuring all kinds of projects that are using Tor. Consider this a late bonus addition to that. ;)
I hope that Tor onion services will continue to develop to make them easier to use for peer-to-peer systems. We can still dream a better Internet.
This work was made possible by all my supporters on Patreon.