tahoe-lafs/docs/anonymity-configuration.rst

Using Tahoe-LAFS with an anonymizing network: Tor, I2P

1. Overview
2. Use cases
3. Native anonymizing network integration for Tahoe-LAFS
   1. Unresolved tickets
4. Software Dependencies
   1. Tor
   2. I2P
5. Connection configuration
6. Anonymity configuration
   1. Client anonymity
   2. Server anonymity
7. Performance and security issues with Tor Hidden Services
8. Performance and security issues with I2P
9. Torsocks: the old way of configuring Tahoe-LAFS to use Tor
10. Legacy I2P Tahoe-LAFS Configuration

Overview

Tor is an anonymizing network used to help hide the identity of internet clients and servers. Please see the Tor Project's website for more information: https://www.torproject.org/

I2P is a decentralized anonymizing network that focuses on end-to-end anonymity between clients and servers. Please see the I2P website for more information: https://geti2p.net/

Use cases

There are three potential use-cases for Tahoe-LAFS on the client side:

1. User does not care to protect their anonymity or to connect to anonymous storage servers. This document is not useful to you... so stop reading.
2. User does not care to protect their anonymity but they wish to connect to Tahoe-LAFS storage servers which are accessible only via Tor Hidden Services or I2P.
   • Tor is only used if a server endpoint string has a .onion address.
   • I2P is only used if a server endpoint string has a .i2p address.
3. User wishes to always use an anonymizing network (Tor, I2P) to protect their anonymity when connecting to Tahoe-LAFS storage grids (whether or not the storage servers are anonymous).

For Tahoe-LAFS storage servers there are three use-cases:

1. Storage server operator does not care to protect their own anonymity nor to help the clients protect theirs. Stop reading this document and run your Tahoe-LAFS storage server using publicly routed TCP/IP.

2. The operator does not require anonymity for the storage server, but they want it to be available over both publicly routed TCP/IP and through an anonymizing network (I2P, Tor Hidden Services). One possible reason to do this is because being reachable through an anonymizing network is a convenient way to bypass NAT or firewall that prevents publicly routed TCP/IP connections to your server. Another is that making your storage server reachable through an anonymizing network can provide better protection for your clients who themselves use that anonymizing network to protect their anonymity.

   See this Tor Project page for more information about Tor Hidden Services: https://www.torproject.org/docs/hidden-services.html.en

   See this I2P Project page for more information about I2P: https://geti2p.net/en/about/intro

3. The operator wishes to protect their anonymity by making their Tahoe server accessible only over I2P, via Tor Hidden Services, or both.

Native anonymizing network integration for Tahoe-LAFS

Tahoe-LAFS utilizes the Twisted endpoints API:

• https://twistedmatrix.com/documents/current/core/howto/endpoints.html

Twisted's endpoint parser plugin system is extensible via installing additional Twisted packages. Tahoe-LAFS utilizes this extensibility to support native Tor and I2P integration.

• Native Tor integration uses the txsocksx and txtorcon modules.
• Native I2P integration uses the txi2p module.

Unresolved tickets

Although the Twisted endpoint API is very flexible it is missing a feature so that servers can be written in an endpoint agnostic style. We've opened a Twisted trac ticket for this feature here:

• https://twistedmatrix.com/trac/ticket/7603

Once this ticket is resolved then an additional changes can be made to Foolscap so that it's server side API is completely endpoint agnostic which will allow users to easily to use Tahoe-LAFS with many protocols on the server side.

txsocksx will try to use the system tor's SOCKS port if available; attempts are made on ports 9050 and 9151. Currently the maintainer of txsocksx has not merged in our code for the Tor client endpoint. We'll use this branch until the Tor endpoint code is merged upstream:

• https://github.com/david415/txsocksx/tree/endpoint_parsers_retry_socks

txtorcon will use the system tor control port to configure Tor Hidden Services pending resolution of tor trac ticket 11291:

• https://trac.torproject.org/projects/tor/ticket/11291

See also Tahoe-LAFS Tor related tickets #1010 and #517.

I2P endpoints (and potentially other endpoint types) require the ability to append a preconfigured set of parameters to any server-provided client endpoint string. See Tahoe-LAFS ticket #2293 for progress.

Software Dependencies

Tor

• Tor (tor) must be installed. See here: https://www.torproject.org/docs/installguide.html.en

• txsocksx must be installed :

  pip install txsocksx

• For storage servers, txtorcon must be installed :

  pip install txtorcon

I2P

• I2P must be installed. See here: https://geti2p.net/en/download

• The SAM API must be enabled.

  • Start I2P.
  • Visit http://127.0.0.1:7657/configclients in your browser.
  • Under "Client Configuration", check the "Run at Startup?" box for "SAM application bridge".
  • Click "Save Client Configuration".
  • Click the "Start" control for "SAM application bridge", or restart I2P.

• txi2p must be installed :

  pip install txi2p

Connection configuration

[connections]

tcp.socks-proxy = (string, optional)

When this option is present, Tahoe-LAFS will install a plugin that routes regular internet connections through a SOCKS proxy.

tor.socks-proxy = (string, optional)

When this option is present, Tahoe-LAFS will install a plugin that handles Tor Hidden service (.onion) connections for clients. If provided but left blank, the plugin will try the default Tor SOCKS proxy ports.

i2p.sam-api = (string, optional)

When this option is present, Tahoe-LAFS will install a plugin that handles I2P connections. If provided but left blank, the plugin will use the default SAM port on localhost.

Anonymity configuration

Tahoe-LAFS provides a configuration flag for explicitly stating whether or not anonymity is required for a node:

[node]
anonymous = (boolean, optional)

Setting anonymous = True causes several changes in the behavior of Tahoe-LAFS:

1. Tahoe-LAFS will not start if any of the configuration options in tahoe.cfg would compromise the identity of the node.
   • In particular, tub.location is forced to either be empty, or contain safe values. It is an error to specify a tub.location that contains anything other than a comma-separated list of location hints for supported anonymizing networks.
2. Tahoe-LAFS will not make any outgoing connections that are not over a supported anonymizing network.
   • If a server's FURL contains one or more location hints for anonymizing networks, Tahoe-LAFS will prefer those hints to connect to the server. An anonymizing network location hint will only be used if the correct modules are installed (see Connection configuration above).
   • If a server's FURL contains no location hints for anonymizing networks (or Tahoe-LAFS could not contact the server via any of the provided anonymizing network location hints), and the user has the required modules for Tor installed, Tahoe-LAFS will connect to the server using Tor as an anonymizing proxy.
   • In all other cases, Tahoe-LAFS will never connect to the server.

This option is critical to preserving the client's anonymity (client use-case 3 from Use cases, above). It is also necessary to preserve a server's anonymity (server use-case 3).

Client anonymity

To configure a client node for anonymity, tahoe.cfg must contain the following configuration flags:

[node]
anonymous = True
tub.location =

Once the Tahoe-LAFS node has been restarted, it can be used anonymously (client use-case 3).

Server anonymity

To configure a server node to listen on an anonymizing network, a corresponding server endpoint descriptor string must be specified in tahoe.cfg:

tub.location = onion:80:hiddenServiceDir=/var/lib/tor/my_service

Multiple anonymizing networks are supported by specifying multiple server endpoint strings, separated by commas:

tub.location = onion:80:hiddenServiceDir=/var/lib/tor/my_service,i2p:/var/lib/i2p/my_service.keypair

To configure a server node for anonymity, anonymous must be set to True (as for the client node case), and tub.location must only contain endpoint strings for supported anonymizing networks. A complete configuration for server use-case 3 would look like:

[node]
anonymous = True
tub.location = onion:80:hiddenServiceDir=/var/lib/tor/my_service,i2p:/var/lib/i2p/my_service.keypair

If server anonymity is not required (server use-case 2 from Use cases above) then tub.location can contain server endpoint strings for non-anonymizing networks:

tub.location = tcp:123.456.789.0:80,onion:80:hiddenServiceDir=/var/lib/tor/my_service

The special string AUTO tells Tahoe-LAFS to try to detect the public interface and use it:

tub.location = "AUTO,onion:80:hiddenServiceDir=/var/lib/tor/my_service"

It is an error to specify a tub.location value that contains AUTO or server endpoint strings for non-anonymizing networks when anonymous is set to True. anonymous must either be unset, or set to False. A complete configuration for server use-case 2 would look like:

[node]
anonymous = False
tub.location = AUTO,onion:80:hiddenServiceDir=/var/lib/tor/my_service,i2p:/var/lib/i2p/my_service.keypair

Performance and security issues with Tor Hidden Services

If you are running a server which does not itself need to be anonymous, should you make it reachable as a Tor Hidden Service or not? Or should you make it reachable both as a Tor Hidden Service and as a publicly traceable TCP/IP server?

There are several trade-offs effected by this decision.

NAT/Firewall penetration

Making a server be reachable as a Tor Hidden Service makes it reachable even if there are NATs or firewalls preventing direct TCP/IP connections to the server.

Anonymity

Making a Tahoe-LAFS server accessible only via Tor Hidden Services can be used to guarantee that the Tahoe-LAFS clients use Tor to connect. This prevents misconfigured clients from accidentally de-anonymizing themselves by connecting to your server through the traceable Internet.

Also, interaction, through Tor, with a Tor Hidden Service may be more protected from network traffic analysis than interaction, through Tor, with a publicly traceable TCP/IP server.

XXX is there a document maintained by Tor developers which substantiates or refutes this belief? If so we need to link to it. If not, then maybe we should explain more here why we think this?

Performance

A client connecting to a Tahoe-LAFS server through Tor incurs substantially higher latency and sometimes worse throughput than the same client connecting to the same server over a normal traceable TCP/IP connection.

A client connecting to a Tahoe-LAFS server which is a Tor Hidden Service incurs much more latency and probably worse throughput.

Positive and negative effects on other Tor users

Sending your Tahoe-LAFS traffic over Tor adds cover traffic for other Tor users who are also transmitting bulk data. So that is good for them -- increasing their anonymity.

However, it makes the performance of other Tor users' interactive sessions -- e.g. ssh sessions -- much worse. This is because Tor doesn't currently have any prioritization or quality-of-service features, so someone else's ssh keystrokes may have to wait in line while your bulk file contents get transmitted. The added delay might make other people's interactive sessions unusable.

Both of these effects are doubled if you upload or download files to a Tor Hidden Service, as compared to if you upload or download files over Tor to a publicly traceable TCP/IP server.

Performance and security issues with I2P

TBC

Torsocks: the old way of configuring Tahoe-LAFS to use Tor

Before the native Tor integration for Tahoe-LAFS, users would use Torsocks. Please see these pages for more information about Torsocks:

• https://code.google.com/p/torsocks/
• https://trac.torproject.org/projects/tor/wiki/doc/torsocks
• https://github.com/dgoulet/torsocks/

Starting And Stopping

Assuming you have your Tahoe-LAFS node directory placed in ~/.tahoe, use Torsocks to start Tahoe like this:

usewithtor tahoe start

Likewise if restarting, then with Torsocks like this:

usewithtor tahoe restart

After Tahoe is started, additional Tahoe commandline commands will not need to be executed with Torsocks because the Tahoe gateway long running process handles all the network connectivity.

Configuration

Before Tahoe-LAFS had native Tor integration it would deanonymize the user if a tub.location value is not set. This is because Tahoe-LAFS at that time defaulted to autodetecting the external IP interface and announced that IP address to the server.

Tahoe-LAFS + Torsocks client configuration

NOTE: before diving into Tor + Tahoe-LAFS configurations you should ensure your familiarity with with installing Tor on unix systems. If you intend to operate an anonymous Tahoe-LAFS storage node then you will also want to read about configuring Tor Hidden Services. See here:

https://www.torproject.org/docs/tor-doc-unix.html.en

https://www.torproject.org/docs/tor-hidden-service.html.en

Run a node using torsocks, in client-only mode (i.e. we can make outbound connections, but other nodes will not be able to connect to us). The literal 'client.fakelocation' will not resolve, but will serve as a reminder to human observers that this node cannot be reached. "Don't call us.. we'll call you":

tub.port = tcp:interface=127.0.0.1:8098
tub.location = client.fakelocation:0

Tahoe-LAFS + Torsocks storage server configuration

Run a node behind a Tor proxy, and make the server available as a Tor "hidden service". (This assumes that other clients are running their node with torsocks, such that they are prepared to connect to a .onion address.) Your instance of Tor should be configured for Hidden Services... for instance specify the Hidden Service listening on port 29212 should proxy to 127.0.0.1 port 8098 by adding this to your torrc :

HiddenServiceDir /var/lib/tor/services/tahoe-storage
HiddenServicePort 29212 127.0.0.1:8098

once Tor is restarted, the .onion hostname will be in /var/lib/tor/services/tahoe-storage/hostname. Then set up your tahoe.cfg like:

tub.port = tcp:interface=127.0.0.1:8098
tub.location = ualhejtq2p7ohfbb.onion:29212

Troubleshooting

On some NetBSD systems, torsocks may segfault:

$ torsocks telnet www.google.com 80
Segmentation fault (core dumped)

and backtraces show looping libc and syscalls:

#7198 0xbbbda26e in *__socket30 (domain=2, type=1, protocol=6) at socket.c:64
#7199 0xbb84baf9 in socket () from /usr/lib/libc.so.12
#7200 0xbbbda19b in tsocks_socket (domain=2, type=1, protocol=6) at socket.c:56
#7201 0xbbbda26e in *__socket30 (domain=2, type=1, protocol=6) at socket.c:64
#7202 0xbb84baf9 in socket () from /usr/lib/libc.so.12
[...etc...]

This has to do with the nature of the torsocks socket() call wrapper being unaware of NetBSD's internal binary backwards compatibility.

Information on a the first parts of a solution patch can be found in a tor-dev thread here from Thomas Klausner:

• https://lists.torproject.org/pipermail/tor-dev/2013-November/005741.html

As of this writing, torsocks still exists in the pkgsrc wip tree here:

• http://pkgsrc.se/wip/torsocks

but the NetBSD-specific patches have been merged upstream into torsocks as of commitid 6adfba809267d9c217906d6974468db22293ab9b:

• https://gitweb.torproject.org/torsocks.git/commit/6adfba809267d9c217906d6974468db22293ab9b

Legacy I2P Tahoe-LAFS Configuration

TBC