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Using Tahoe-LAFS with Tor
- Use cases
- Native Tor integration for Tahoe-LAFS
- Software Dependencies
- Configuration
- Performance and security issues of Tor Hidden Services
Use cases
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/
There are three potential use-cases for Tahoe-LAFS on the client side:
- 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.
- User does not care to protect their anonymity but they wish to connect to Tahoe-LAFS storage servers which are accessbile only via Tor Hidden Services.
- User wishes to always use Tor to protect their anonymity when connecting to Tahoe-LAFS storage grids (whether or not the storage servers are Tor Hidden Services) [*].
For Tahoe-LAFS storage servers there are three use-cases:
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.
The operator does not require anonymity for his storage server, but he wants it to be available over both publicly routed TCP/IP and through Tor Hidden Services. One possible reason to do this is because being reachable through Tor Hidden Services 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 Tor Hidden Services can provide better protection for your clients who themselves use Tor 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
The operator wishes to protect their anonymity by making their Tahoe server accessible only via Tor Hidden Services.
Native Tor integration for Tahoe-LAFS
Native Tor integration for 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. The native Tor integration for Tahoe-LAFS uses txsocksx and txtorcon.
txsocksx will try to use the system tor's SOCKS port if available; attempts are made on ports 9050 and 9151.
txtorcon will use the system tor control port to configure Tor Hidden Services ( pending resolution of tor trac ticket https://trac.torproject.org/projects/tor/ticket/11291 )
See also Tahoe-LAFS Tor related tickets #1010 and #517.
Software Dependencies
Tor (tor) must be installed. See here: https://www.torproject.org/docs/installguide.html.en
The "Tor-friendly" branch of txsocksx must be installed ( Once this is merged then you can use upstream txsocksx; https://github.com/habnabit/txsocksx/pull/8 ) :
pip install git+https://github.com/david415/txsocksx.gittxtorcon must be installed :
pip install txtorcon
Once these software dependencies are installed and the Tahoe-LAFS node is restarted, then no further configuration is necessary for "unsafe" Tor connectivity to other Tahoe-LAFS nodes (client use-case 2 from Use cases, above).
In order to implement client use-case 3 or server use-cases 2 or 3, further configuration is necessary.
Configuration
[node] tor_only.enabled = (boolean, optional)
- This specifies two changes in behavior:
- Transform all non-Tor client endpoints into Tor client endpoints.
- Force
tub.locationto be set to "safe" values.
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).
When tor_only.enabled is specified then tub.location does not need to be specified... and it is an error to specify a tub.location value that contains anything other than "UNREACHABLE" or a Tor Hidden Service Twisted endpoint descriptor string.
If server use-case 2 from Use cases above is desired then you can set tub.location to a Tor Hidden Service endpoint string AND "AUTODETECT" like this:: tub.location = "AUTODETECT,onion:80:hiddenServiceDir=/var/lib/tor/my_service"
It is an error to specify a tub.location value that contains "AUTODETECT" when tor_only.enabled is also set to true.
Operators of Tahoe-LAFS storage servers wishing to protect the identity of their storage server should set tor_only.enabled to true and specify a Tor Hidden Service endpoint descriptor string for the tub.location value in the tahoe.cfg like this:: tub.location = "onion:80:hiddenServiceDir=/var/lib/tor/my_service"
Setting this configuration option is necessary for Server use-cases 2 and 3 (from Use cases, above).
Performance and security issues of 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 hackers 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.