git-annex/ design/ assistant/ telehash

Telehash for secure P2P communication between git-annex (assistant) repositories.

Or something similar like Snow or cjdns or tor or i2p or magic wormhole.

## telehash implementation status

- node.js version seems almost complete
- C version currently lacks channel support and seems buggy (13 Jan 2014)
- No pure haskell implementation of telehash v2. There was one of telehash v1 (even that seems incomplete). I have pinged its author to see if he anticipates updating it.
- Rapid development, situation may change in a month or 2. (2014)
  Not seeing many commits now (2015)
- Is it secure? A security review should be done by competant people (not Joey). See https://github.com/telehash/telehash.org/issues/23
- Haskell version https://github.com/alanz/htelehash/tree/v2/src/TeleHash May support v2; v3 support seems not started yet, and not in active development at the moment, although there has been work on it a year ago.
- Not very convinced this is going to be usable anytime soon, so would like to find something that is. (2015)

## snow status

- Seems ready to use?
- NAT punching works per docs; relies on a DHT network for hole punching, and the reliabilty of that network is not known. I notice it has only 1 pre-seeded peer in the source tree for the DHT, and that peer was not up when I tried it.
- Only provides network-layer transport, still need to implement some file transfer protocol on top.

## cjdns status

- Has a network with "hundreds of active nodes"
- Is not pure P2P; there's a network that does routing of packets. This may be a good thing, or not.
- Seems to require manual configuration of a "friend" node that's already on the network, with address and password to connect to it, so if you can't find someone you know to connect to their node, you can't use it. Urk.

## tor status

- Awesome.
- Easy to install, use; very well known.
- Supported in git-annex now!

## i2p status

## magic wormhole

- simple file transfer protocol with out of band shared secret
- handles NAT transversal
- easy to use
- doesn't require a running daemon
- can transfer arbitrary blobs (strings, directories, files)

## general design

- There is a generic P2P protocol, which should be usable with any P2P system that can send messages between peers.
- A p2p remote has an url like tor-annex::fijdksajdksjfkj, which connects to a specific peer. The peer's address may be kept private, but the design allows the address to be public without giving access to the peer.
- An authtoken also needs to be presented when connecting with a peer. This is stored in local creds storage and must be kept private.
- The remotedaemon runs, and/or communicates with the program implementing the P2P network. For example for tor, the remotedaemon runs the hidden service.
- The remotedaemon handles both sides of git push over the transport.
- The remotedaemon may also support sending objects over the transport, depending on the transport.

## address exchange

The address is a public key, and the authtoken is some large chunk of data, so won't want to type that in. Need discovery or exchange for peering.

- Easy way is any set of repos that are already connected can communicate them via address.log.
- Address and authtoken can be communicated out of band (eg, via an OTR session or gpg encrypted mail or phone call), and pasted into the webapp.
- Use eg, electrum-mnemonic to encode the address+authtoken so that it can be read over the phone.
- Users may not have a way to communicate with perfect forward secrecy. So it would be good to have a address+authtoken that can only be used one time during pairing.
- Check out PAKE for MITM resistance.

- Possibly use magic wormhole to exchange the address, which avoids the users needing to exchange so much data. The magic wormhole code is just 3 words, and it uses PAKE.

  I tried it, and opened a couple of bug reports that would be useful in integrating it with git-annex:

  - option to receive to a specific file
  - machine readable wormhole code

## local lan detection

At connection time, after authentication, the remote can send (ip address, ssh host key). Try sshing to the ip address to check if the host key matches. If so, can enable a ssh remote, which will be cheaper than using the transport. Send the ssh public key back to the remote to get it authorized.

## remotedaemon

See git-remote-daemon for its design.

Advantages:

- `git annex sync` could also use the running daemon
- `git-remote-$transport` could use the running daemon
- c-telehash might end up linked to openssl, which has licence combination problems with git-annex. A separate process not using git-annex's code would avoid this.
- Allows the daemon to be written in some other language if necessary (for example, if c-telehash development stalls and the nodejs version is already usable)
- Potentially could be generalized to handle other similar protocols. Or even the xmpp code moved into it. There could even be git-annex native exchange protocols implemented in such a daemon to allow SSH-less transfers.
- Security holes in telehash would not need to compromise the entire git-annex. daemon could be sandboxed in one way or another.

Disadvantages:

- Adds some complexity.

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