Version 19 (modified by sambhav2612, 3 years ago) (diff)

fix grammatical errors

Projects for the core Tor implementation:


The tor program implements the core client and server code for participating in the Tor network. The source is available at

Active Projects

  • Increase Tor's suitability as a circumvention tool based on designs stated in "Design of a blocking-resistant anonymity system" (sponsor A, deliverables 1 and 2)
  • Facilitate reconfiguration of clients to bridges (sponsor A, deliverable 3)
  • Hide Tor's network fingerprint even more (sponsor A, deliverable 5)
  • Enhance Tor's cell-based and directory protocol to improve performance in low-bandwidth/high-latency/high-packet-loss networks (sponsor A, deliverable 6)
  • Make Tor scale to 2 million concurrent users by splitting the network into multiple segments, switching to datagram-based protocols, and improving load balancing within the network (sponsor A, deliverables 7 and 13)
  • Improve usability, performance, and reliability of bridges (sponsor A, deliverable 12)
  • Research the option of providing incentives to run Tor relays (sponsor A, deliverable 14)
  • Split AES and SSL across multiple cores. (#1749) (Sponsor D, deliverable 19 for Sep 30: Initial design, maybe code.)
  • Finish integrating a microdescriptor implementation. (#1748) (Sponsor D, deliverable 8 for Sep 30)
  • Release candidate for Tor 0.2.2.x. (Tor: 0.2.2.x-final) (Sponsor D, deliverable 18 for Sep 30: release an RC)
  • Add support for bufferevent-based data transports. (#1761)
  • See if we can improve performance by throttling streams at guard nodes (#1750) (Sponsor D, deliverable 2 for Sep 30)
  • Make it harder to use exit nodes as one-hop proxies. (#1751) (Sponsor D, deliverable 3 for Sep 30)
  • Make it so all clients can get promoted to bridges. (#1752) (Sponsor D, deliverable 6 for Sep 30: design and initial progress)
  • Improve reliability for Windows relays. (#1753) (sponsor D, deliverable 20 for Sep 30: analysis and progress on bufferevents)
  • IPv6 support in Tor

Future ideas

  • Add support for advertising directory mirrors that have no DirPort, but only support BEGIN_DIR.
  • Make Tor able to relay more open-formed DNS requests to the exit node's DNS; expand DNSPort to handle TCP DNS requests as needed.
  • Instrument Tor's internals more thoroughly to identify bottlenecks.
  • Perhaps, make all bridges also able to proxy connections to the Tor download site.
  • Switch to a UDP transport.

Imported future ideas from TODO.future

Many of these may be stale. Move them from here to the "Future Ideas" section if they're still desirable ideas.

Later, unless people want to implement them now:

  • Actually use SSL_shutdown to close our TLS connections.
  • Include "v" line in networkstatus getinfo values.
    • [Nick: bridge authorities output a networkstatus that is missing version numbers. This is inconvenient if we want to make sure bridgedb gives out bridges with certain characteristics. -RD]
    • [Okay. Is this a separate item, or is it the same issue as the lack of a "v" line in response to the controller GETINFO command? -NM]
  • MAYBE kill stalled circuits rather than stalled connections. This is possible thanks to cell queues, but we need to consider the anonymity implications.
  • Make resolves no longer use edge_connection_t unless they are actually _on_ a socks connection: have edge_connection_t and (say) dns_request_t both extend an edge_stream_t and have p_streams and n_streams both be linked lists of edge_stream_t.
  • Generate torrc.{complete|sample}.in,, the HTML manual, and the online config documentation from a single source.
  • It would be potentially helpful to respond to https requests on the OR port by acting like an HTTPS server.
  • We should get smarter about handling address resolve failures, or addresses that resolve to local IPs. It would be neat to retry them since right now we just close the stream. But we need to make sure we don't retry them on the same exit as before. But if we mark the circuit, then any user who types "localhost" will cycle through circuits till they run out of retries. See bug #872.

Can anybody remember why we wanted to do this and/or what it means?

  • config option __ControllerLimit that hangs up if there are a limit of controller connections already.
    • [This was mwenge's idea. The idea is that a Tor controller can "fill" Tor's controller slot quota, so jerks can't do cross-protocol attacks like the HTTP form attack. -RD]
  • Bridge issues:
    • Ask all directory questions to bridge via BEGIN_DIR.
    • use the bridges for dir fetches even when our dirport is open.
    • drop 'authority' queries if they're to our own identity key; accept them otherwise.
    • give extend_info_t a router_purpose again

If somebody wants to do this in some version, they should:

  • Create packages for Maemo/Nokia 800/810, requested by Chris Soghoian
    • Debian already makes ARM-arch debs, can maemo use these asks phobos?
  • More work on AvoidDiskWrites
  • Make DNSPort support TCP DNS.

Roger, please sort these:

  • bridge communities with local bridge authorities:
  • clients who have a password configured decide to ask their bridge authority for a networkstatus
  • be able to have bridges that aren't in your torrc. save them in the state file, etc.
  • Consider if we can solve: the Tor client doesn't know what flags its bridge has (since it only gets the descriptor), so it can't make decisions based on Fast or Stable.
  • Some mechanism for specifying that we want to stop using a cached bridge.

Future versions:


  • Our current approach to block attempts to use Tor as a single-hop proxy is pretty lame; we should get a better one.
  • Allow small cells and large cells on the same network?
  • Cell buffering and resending. This will allow us to handle broken circuits as long as the endpoints don't break, plus will allow connection (TLS session key) rotation.
  • Implement MorphMix (another paper), so we can compare its behavior, complexity, etc. But see paper breaking morphmix.
  • Other transport. HTTP, UDP, RDP, airhook, etc. May have to do our own link crypto unless we can bully DTLS into it.
  • Need a relay teardown cell, separate from one-way ends. (Pending a user who needs this)
  • Handle half-open connections: right now we don't support all TCP streams, at least according to the protocol. But we handle all that we've seen in the wild. (Pending a user who needs this)

Directory system:

  • BEGIN_DIR items
    • handle connect-dir streams that don't have a chosen_exit_name set.
    • Have a "Faster" status flag that means it. Fast2, Fast4, Fast8?
    • Add an option (related to AvoidDiskWrites) to disable directory caching. (Is this actually a good idea??)
    • X Add d64 and fp64 along-side d and fp so people can paste status entries into a URL. since + is a valid base64 char, only allow one at a time. Consider adding to a controller as well. [abandoned for lack of demand]
    • Some back-out mechanism for auto-approval on authorities
      • a way of rolling back approvals to before a timestamp
        • Consider minion-like fingerprint file/log combination.
    • X Have new people be in limbo and need to demonstrate the usefulness before we approve them.

Hidden services:

  • d Standby/hotswap/redundant hidden services: needs a proposal.
  • you can insert a hidserv descriptor via the controller.
  • auth mechanisms to let hidden service midpoint and responder filter connection requests: proposal 121.
  • Let each hidden service (or other things) specify its own OutboundBindAddress?

Server operation:

  • If the server is spewing complaints about raising your ulimit -n, we should add a note about this to the server descriptor so other people can notice too.
  • When we hit a funny error from a dir request (eg 403 forbidden), but tor is working and happy otherwise, and we haven't seen many such errors recently, then don't warn about it.


  • Implement missing status events and accompanying getinfos
    • BAD_DIR_RESPONSE (Unexpected directory response; maybe we're behind a firewall.)
    • BAD_PROXY (Bad HTTP or https proxy)
    • UNRECOGNIZED_ROUTER (a nickname we asked for is unavailable)
    • Status events related to hibernation
    • something about failing to parse our address? from resolve_my_address() in config.c
    • sketchy OS, sketchy threading
    • too many onions queued: threading problems or slow CPU?
  • Implement missing status event fields:
    • GETINFO status/client, status/server, status/general: There should be some way to learn which status events are currently "in effect." We should specify which these are, what format they appear in, and so on.
    • More information in events:
      • Include bandwidth breakdown by conn->type in BW events.
      • Change circuit status events to give more details, like purpose, whether they're internal, when they become dirty, when they become too dirty for further circuits, etc.
      • Change stream status events analogously.
    • Expose more information via getinfo:
      • import and export rendezvous descriptors
      • Review all static fields for additional candidates
    • Allow EXTENDCIRCUIT to an unknown server.
      • We need some way to adjust server status and to tell Tor not to download directories/network-status, and a way to force a download.
      • Make everything work with hidden services


  • per-conn write buckets
  • separate config options for read vs write limiting. (It's hard to support read > write, since we need better congestion control to avoid overfull buffers there. So, defer the whole thing.)
  • Rate limit exit connections to a given destination -- this helps us play nice with websites when Tor users want to crawl them; it also introduces DoS opportunities.
  • Consider truncating rather than destroying failed circuits, in order to save the effort of restarting. There are security issues here that need thinking, though.
  • Handle full buffers without totally borking
  • Rate-limit OR and directory connections overall and per-IP and maybe per subnet.


  • Hold-open-until-flushed now works by accident; it should work by design.
  • Display the reasons in 'destroy' and 'truncated' cells under some circumstances?
  • Make router_is_general_exit() a bit smarter once we're sure what it's for.
  • Automatically determine what ports are reachable and start using those, if circuits aren't working and it's a pattern we recognize ("port 443 worked once and port 9001 keeps not working").


  • some better fix for bug #516?
  • Directory guards
  • Mini-SoaT:
    • Servers might check certs for known-good SSL websites, and if they come back self-signed, declare themselves to be non-exits. Similar to how we test for broken/evil DNS now.
    • Authorities should try using exits for HTTP to connect to some URLs (specified in a configuration file, so as not to make the List Of Things Not To Censor completely obvious) and ask them for results. Exits that don't give good answers should have the BadExit flag set.
    • Alternatively, authorities should be able to import opinions from Snakes on a Tor.
  • Bind to random port when making outgoing connections to Tor servers, to reduce remote sniping attacks.
  • Audit everything to make sure rend and intro points are just as likely to be us as not.
  • Do something to prevent spurious EXTEND cells from making middleman nodes connect all over. Rate-limit failed connections, perhaps?
  • DoS protection: TLS puzzles, public key ops, bandwidth exhaustion.

Needs thinking:

  • Now that we're avoiding exits when picking non-exit positions, we need to consider how to pick nodes for internal circuits. If we avoid exits for all positions, we skew the load balancing. If we accept exits for all positions, we leak whether it's an internal circuit at every step. If we accept exits only at the last hop, we reintroduce Lasse's attacks from the Oakland paper.

Windows server usability:

  • Solve the ENOBUFS problem.
    • make tor's use of OpenSSL operate on buffers rather than sockets, so we can make use of libevent's buffer paradigm once it has one.
    • make tor's use of libevent tolerate either the socket or the buffer paradigm; includes unifying the functions in connect.c.
  • We need a getrlimit equivalent on Windows so we can reserve some file descriptors for saving files, etc. Otherwise, we'll trigger asserts when we're out of file descriptors and crash.


  • a way to generate the website diagrams from source, so we can translate them as UTF-8 text rather than with gimp. (SVG or ImageMagick?)
  • Flesh out options_description array in src/or/config.c
  • multiple samples torrc files
  • Refactor Tor man page to divide generally useful options from less useful ones?
  • Add a Doxygen style checker to make check-spaces so nick doesn't drift too far from arma's undocumented style guide. Also, the document that style guide in HACKING. (See r9634 for example.)
    • exactly one space at the beginning and at end of comments, except I guess when there's line-length pressure.
    • if we refer to a function name, put a () after it.
    • only write <b>foo</b> when foo is an argument to this function.
    • Doxygen comments must always end in some form of punctuation.
    • capitalize the first sentence in the Doxygen comment, except when you shouldn't.
    • avoid spelling errors and incorrect comments. ;)


Blue-sky projects