tor/doc/TODO

$Id$
Legend:
SPEC!!  - Not specified
SPEC    - Spec not finalized
N       - nick claims
R       - arma claims
P       - phobos claims
        - Not done
        * Top priority
        . Partially done
        o Done
        d Deferrable
        D Deferred
        X Abandoned

Temporary notations for moving items around:
++      - Make this a task for the current version
d       - Move this into "nice to have for the current version"
D       - Move this into "deferred from current version."
X2      - This is a duplicate; remove it.

Documentation and testing on 0.1.2.x-final series

  o Test guard unreachable logic; make sure that we actually attempt to
    connect to guards that we think are unreachable from time to time.
    Make sure that we don't freak out when the network is down.

++. Forward compatibility fixes
N   - Hack up a client that gives out weird/no certificates, so we can
      test to make sure that this doesn't cause servers to crash.

++. Finish path-spec.txt

++- Docs
    - Tell people about OSX Uninstaller
    - Quietly document NT Service options
    - More prominently, we should have a recommended apps list.
      - recommend gaim.
      - unrecommend IE because of ftp:// bug.
    - we should add a preamble to tor-design saying it's out of date.
    . Document transport and natdport
      o In man page
      - In a good HOWTO.

Things we'd like to do in 0.2.0.x:
      - Bug reports Roger has heard along that way that don't have enough
        details/attention to solve them yet.
        - tup said that when he set FetchUselessDescriptors, after
          24 or 48 hours he wasn't fetching any descriptors at all
          anymore. This was in 0.2.0 but worked fine in 0.1.2.
        - arma noticed that when his network went away and he tried
          a new guard node and the connect() syscall failed to it,
          the guard wasn't being marked as down. 0.2.0.x.
        - after being without network for 12 hours, arma's tor decided
          it couldn't fetch any network statuses, and never tried again
          even when the network came back and arma clicked on things.
          also 0.2.0.
        - phobos says relaybandwidth* sometimes don't do what we expect.
          http://interloper.org/tmp/2007-06-bw-usage.png
        - this notion of authorities notifying servers that they're
          unreachable is bunk -- it's leftover from the time when all
          servers ran 24/7. now it triggers every time a server goes
          away and then returns before the old descriptor has expired.
      - add a --quiet commandline option that suppresses logs. useful
        for --hashed-password and maybe others.

  - Proposals:
    . 101: Voting on the Tor Directory System (plus 103)
      . Finalize proposal
        * Describe schedule in copious detail.
      - Get authorities voting
        . Code to manage key certificates
          - Download as needed.
        . Code to generate consensus from a list of votes
          * Detect whether votes are really all for the same period.
        . Push/pull documents as appropriate.
          - Pull votes and signatures if we don't get them.
        - Cache votes and signatures on disk.
        o Have clients know which authorities are v3 authorities, and what
          their keys are.
          - While we're at it, let v3 authorities have fqdns lines.
        - Fix all XXXX020s in vote code
      - Validate information properly.
        - Warn if we get a vote with different authorities than we know.
        - Don't count votes with a different valid-after when generating
          the same consensus.
        - Dump certificates with the wrong time.  Or just warn?
        - Warn authority ops when their certs are nearly invalid.
        - When checking a consensus, make sure that its times are plausible.
        - Add a function that will eventually tell us about our clock skew.
          For now, just require that authorities not be skewed.
      - Start caching consensus documents once authorities make them
      - Start downloading and using consensus documents once caches serve them
      - Controller support
        - GETINFO to get consensus
        - Event when new consensus arrives
    . 104: Long and Short Router Descriptors
      - Drop bandwidth history from router-descriptors
    - 105: Version negotiation for the Tor protocol
d   - 113: Simplifying directory authority administration
d   - 110: prevent infinite-length circuits (phase one)
      - servers should recognize relay_extend cells and pass them
        on just like relay cells

  - Refactoring:
D   - 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.
    . Make cells get buffered on circuit, not on the or_conn.
      . Switch to pool-allocation for cells?
        - Benchmark pool-allocation vs straightforward malloc.
        - Adjust memory allocation logic in pools to favor a little less
          slack memory.
d     - MAYBE kill stalled circuits rather than stalled connections; consider
        anonymity implications.
d   - Move all status info out of routerinfo into local_routerstatus.  Make
      "who can change what" in local_routerstatus explicit.  Make
      local_routerstatus (or equivalent) subsume all places to go for "what
      router is this?"
    . Remove socketpair-based bridges conns, and the word "bridge".  (Use
      shared (or connected) buffers for communication, rather than sockets.)
      . Implement
        - Handle rate-limiting on directory writes to linked directory
          connections in a more sensible manner.
        - Find more ways to test this.
    D Generate torrc.{complete|sample}.in, tor.1.in, the HTML manual, and the
      online config documentation from a single source.
    - Have clients do TLS connection rotation less often than "every 10
      minutes" in the thrashy case, and more often than "once a week" in the
      extra-stable case.
    - Streamline how we pick entry nodes: Make choose_random_entry() have
      less magic and less control logic.
d   - Implement TLS shutdown properly when possible.
    - Maybe move NT services into their own module.
    . Autoconf cleanups and improvements:
      o Tell the user what -dev package to install based on OS.
d     - Detect correct version of libraries.
    - Refactor networkstatus generation:
      - Include "v" line in getinfo values.

  - Features:
    - Traffic priorities
      . Ability to prioritize own traffic over relayed traffic.
        (Proposal 111.)
        . Implement
        - Merge proposal into the spec.
    . DNS Proxy
      - Document it
d   - A better UI for authority ops.
      - Follow weasel's proposal, crossed with mixminion dir config format
      - Write a proposal
    . Bridges users (rudimentary version)
      o Ability to specify bridges manually
      o Config option 'UseBridges' that bridge users can turn on.
        o uses bridges as first hop rather than entry guards.
      D Do we want to maintain our own set of entryguards that we use as
        next hop after the bridge? Open research question; let's say no
        for 0.2.0 unless we learn otherwise.
      o if you don't have any routerinfos for your bridges, or you don't
        like the ones you have, ask a new bridge for its server/authority.
      . Ask all directory questions to bridge via BEGIN_DIR.
        - use the bridges for dir fetches even when our dirport is open.
R     - drop 'authority' queries if they're to our own identity key; accept
        them otherwise.
N     - Design/implement the "local-status" or something like it, from the
        "Descriptor purposes: how to tell them apart" section of
        http://archives.seul.org/or/dev/May-2007/msg00008.html
        - cache of bridges that we've learned about and use but aren't
          manually listed in the torrc.
          D and some mechanism for specifying that we want to stop using
            a given bridge in this cache.
      o timeout and retry schedules for fetching bridge descriptors
      - give extend_info_t a router_purpose again
      o react faster to download networkstatuses after the first bridge
        descriptor arrives
      o be more robust to bridges being marked as down and leaving us
        stranded without any known "running" bridges.
    - Bridges operators (rudimentary version)
      - Ability to act as dir cache without a dir port.
      o Bridges publish to bridge authorities
      o Fix BEGIN_DIR so that you connect to bridge of which you only
        know IP (and optionally fingerprint), and then use BEGIN_DIR to learn
        more about it.
      - look at server_mode() and decide if it always applies to bridges too.
    - Bridges authorities (rudimentary version)
      o Rudimentary "do not publish networkstatus" option for bridge
        authorities.
      - Clients can ask bridge authorities for more bridges.
      D Should do reachability testing but only on the purpose==bridge
        descriptors we have.
    - Bridges
      o Clients can ask bridge authorities for updates on known bridges.
      - More TLS normalization work: make Tor less easily
        fingerprinted.
      - Directory system improvements
d       - config option to publish what ports you listen on, beyond
          ORPort/DirPort.  It should support ranges and bit prefixes (?) too.
          (This is very similar to proposal 118.)
d   - Let controller set router flags for authority to transmit, and for
      client to use.
d   - Support relaying streams to ipv6.
      - Internal code support for ipv6:
        o Clone ipv6 functions (inet_ntop, inet_pton) where they don't exist.
        - Most address variables need to become sockaddrs.
        - Teach resolving code how to handle ipv6.
        - Teach exit policies about ipv6 (consider ipv4/ipv6 interaction!)
        - ...
x2  - Let servers decide to support BEGIN_DIR but not DirPort.
      (duplicate of "Ability to act as a dir cache without a dir port.")
    - Blocking-resistance.
      - Write a proposal; make this part of 105.
D   - It would be potentially helpful to https requests on the OR port by
      acting like an HTTPS server.
d   - add an 'exit-address' line in the descriptor for servers that exit
      from something that isn't their published address.
    - Audit how much RAM we're using for buffers and cell pools; try to
      trim down a lot.
    - Accept \n as end of lines in the control protocol in addition to \r\n.
    - Base relative control socket paths on datadir.
  o Deprecations:
    - can we deprecate 'getinfo network-status'?
    - can we deprecate the FastFirstHopPK config option?

P - Packaging:
P   - Can we switch to polipo?
P   - If we haven't replaced privoxy, lock down its configuration in all
      packages, as documented in tor-doc-unix.html
P - Figure out why dll's compiled in mingw don't work right in WinXP.
P - Figure out why openssl 0.9.8e "make test" fails at sha256t test.
P - Figure out if including RSA and IDEA are bad for Tor from a legal
     perspective
P - Create packages for Nokia 800, requested by Chris Soghoian
P - Consider creating special Tor-Polipo-Vidalia test packages,
    requested by Dmitri Vitalev
  - add an AuthDirBadexit torrc option if we decide we want one.

Deferred from 0.1.2.x:   (Unmarked items will become "Future version")
  - BEGIN_DIR items
    - turn the received socks addr:port into a digest for setting .exit
    - handle connect-dir streams that don't have a chosen_exit_name set.
  X 'networkstatus arrived' event
    (Abandoned for simpler version in v3 protocol)
d - More work on AvoidDiskWrites?
  - 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.)
  - don't do dns hijacking tests if we're reject *:* exit policy?
    (deferred until 0.1.1.x is less common)
  - Directory guards
  - RAM use in directory authorities.
  - Memory use improvements:
    - Look into pulling serverdescs off buffers as they arrive.
    X Save and mmap v1 directories, and networkstatus docs; store them
      zipped, not uncompressed.
      (Abandoned in favor of dropping v1 directory support.)
      X Switch cached_router_t to use mmap.
      X What to do about reference counts on windows?  (On Unix, this is
        easy: unlink works fine.  (Right?)  On Windows, I have doubts.  Do we
        need to keep multiple files?)
      X What do we do about the fact that people can't read zlib-
        compressed files manually?

d - If the client's clock is too far in the past, it will drop (or
    just not try to get) descriptors, so it'll never build circuits.
  - Tolerate clock skew on bridge relays.

  - 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.

++- We should ship with a list of stable dir mirrors -- they're not
    trusted like the authorities, but they'll provide more robustness
    and diversity for bootstrapping clients.

  - A way to adjust router flags from the controller.
    (How do we prevent the authority from clobbering them soon after?)

++- Better estimates in the directory of whether servers have good uptime
    (high expected time to failure) or good guard qualities (high
    fractional uptime).
    - AKA Track uptime as %-of-time-up, as well as time-since-last-down

  - Have a "Faster" status flag that means it. Fast2, Fast4, Fast8?
    - spec
    - implement

  - 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.
    - rewrite how libevent does select() on win32 so it's not so very slow.
      - Add overlapped IO

  - Add an option (related to AvoidDiskWrites) to disable directory caching.

  - Finish status event implementation and accompanying getinfos
    - Missing events:
      - DIR_REACHABLE
      - 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?
    - Missing fields:
      - TIMEOUT on CHECKING_REACHABILITY
    - 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.


Minor items for 0.1.2.x as time permits:
  - include bandwidth breakdown by conn->type in BW events.
++- Recommend polipo? Please?
++- Make documentation realize that location of system configuration file
    will depend on location of system defaults, and isn't always /etc/torrc.
d - Review torrc.sample to make it more discursive.
  - a way to generate the website diagrams from source, so we can
    translate them as utf-8 text rather than with gimp.
  - 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. spec and then do.
  - The Debian package now uses --verify-config when (re)starting,
    to distinguish configuration errors from other errors. Perhaps
    the RPM and other startup scripts should too?
  - add a "default.action" file to the tor/vidalia bundle so we can fix the
    https thing in the default configuration:
    http://wiki.noreply.org/noreply/TheOnionRouter/TorFAQ#PrivoxyWeirdSSLPort
  . Flesh out options_description array in src/or/config.c
  X If we try to publish as a nickname that's already claimed, should
    we append a number (or increment the number) and try again? This
    way people who read their logs can fix it as before, but people
    who don't read their logs will still offer Tor servers.
    - Fall back to unnamed; warn user; send controller event.  ("When we
      notice a 'Rejected: There is already a named server with this nickname'
      message... or maybe instead when we see in the networkstatuses that
      somebody else is Named with the name we want: warn the user, send a
      STATUS_SERVER message, and fall back to unnamed.")
  - 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.
x2- Christian Grothoff's attack of infinite-length circuit.
    the solution is to have a separate 'extend-data' cell type
    which is used for the first N data cells, and only
    extend-data cells can be extend requests.
    . Specify, including thought about anonymity implications. [proposal 110]
  - Display the reasons in 'destroy' and 'truncated' cells under some
    circumstances?
  - 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.
  - cpu fixes:
    - see if we should make use of truncate to retry
  . Directory changes
    . Some back-out mechanism for auto-approval
      - a way of rolling back approvals to before a timestamp
        - Consider minion-like fingerprint file/log combination.
  - packaging and ui stuff:
    . multiple sample torrc files
    . figure out how to make nt service stuff work?
      . Document it.
    - Vet all pending installer patches
      - Win32 installer plus privoxy, sockscap/freecap, etc.
      - Vet win32 systray helper code
      (2007-04-15 phobos, do we still need these installer patches?)

  - Improve controller
      - a NEWSTATUS event similar to NEWDESC.
      - 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.
        - What do we want here, exactly?
        - Specify and implement it.
      - Change stream status events analogously.
        - What do we want here, exactly?
        - Specify and implement it.
      - Make other events "better".
      - Change stream status events analogously.
        - What do we want here, exactly?
        - Specify and implement it.
      - Make other events "better" analogously
        - What do we want here, exactly?
        - Specify and implement it.
      . Expose more information via getinfo:
        - import and export rendezvous descriptors
        - Review all static fields for additional candidates
      - Allow EXTENDCIRCUIT to 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

Deferred from 0.2.0:
  - Make a TCP DNSPort

Future version:
  - 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.
d - we try to build 4 test circuits to break them over different
    servers. but sometimes our entry node is the same for multiple
    test circuits. this defeats the point.
  - 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.
  - More consistent error checking in router_parse_entry_from_string().
    I can say "banana" as my bandwidthcapacity, and it won't even squeak.
  - Add a doxygen style checker to make check-spaces so nick doesn't drift
    too far from arma's undocumented styleguide.  Also, document that
    styleguide in HACKING.  (See r9634 for example.)
    - exactly one space at 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. ;)
++- Should TrackHostExits expire TrackHostExitsExpire seconds after their
    *last* use, not their *first* use?
  X Configuration format really wants sections.
++. Good RBL substitute.
    o Play with the implementations; link them from somewhere; add a
      round-robin link from torel.torproject.org; describe how to
      use them in the FAQ.
    o Torel is now implemented.
    - Publicize torel.  (What else?
  - 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.
  - Our current approach to block attempts to use Tor as a single-hop proxy
    is pretty lame; we should get a better one.
  . Update the hidden service stuff for the new dir approach.
    - switch to an ascii format, maybe sexpr?
    - authdirservers publish blobs of them.
    - other authdirservers fetch these blobs.
    - hidserv people have the option of not uploading their blobs.
    - you can insert a blob via the controller.
    - and there's some amount of backwards compatibility.
    - teach clients, intro points, and hidservs about auth mechanisms.
    - come up with a few more auth mechanisms.
  - auth mechanisms to let hidden service midpoint and responder filter
    connection requests.
  - Bind to random port when making outgoing connections to Tor servers,
    to reduce remote sniping attacks.
  - Have new people be in limbo and need to demonstrate usefulness
    before we approve them.
d - Clients should estimate their skew as median of skew from servers
    over last N seconds.
  - Make router_is_general_exit() a bit smarter once we're sure what it's for.
  - 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?
  - 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").
++- Limit to 2 dir, 2 OR, N SOCKS connections per IP.
    - Or maybe close connections from same IP when we get a lot from one.
    - Or maybe block IPs that connect too many times at once.
  - 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.
  - DoS protection: TLS puzzles, public key ops, bandwidth exhaustion.
    - Specify?
  - hidserv offerers shouldn't need to define a SocksPort
    * figure out what breaks for this, and do it.
d - tor should be able to have a pool of outgoing IP addresses
    that it is able to rotate through. (maybe)
    - Specify; implement.
    - Probably this is part of proposal 118's stuff.
  - let each hidden service (or other thing) specify its own
    OutboundBindAddress?

Blue-sky:
  - Patch privoxy and socks protocol to pass strings to the browser.
  - Standby/hotswap/redundant hidden services.
d . Robust decentralized storage for hidden service descriptors.
    (Karsten is working on this.)
x2. The "China problem"
    (This is bridges.)
  - 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, so we can compare its behavior, complexity, etc.
  - Other transport. HTTP, udp, rdp, airhook, etc. May have to do our own
    link crypto, unless we can bully openssl 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)

Non-Coding:
  - Mark up spec; note unclear points about servers
  - Mention controller libs someplace.
  . more pictures from ren. he wants to describe the tor handshake
NR- write a spec appendix for 'being nice with tor'
  - tor-in-the-media page
  - Remove need for HACKING file.
  - Figure out licenses for website material.
  - Specify the keys and key rotation schedules and stuff
P - document http://wiki.noreply.org/noreply/TheOnionRouter/TransparentProxy on freebsd and osx
P - figure out why x86_64 won't build rpms from tor.spec
P - figure out spec files for bundles of vidalia-tor-polipo
P - figure out polipo install scripts for bundles of vidalia-tor-polipo on osx, win32
P - evaluate https://sourceforge.net/projects/kleanup/
P - evaluate TorK
P - figure out selinux policy for tor
P - change packaging system to more automated and specific for each
     platform, suggested by Paul Wouter

Website:
  - and remove home and make the "Tor" picture be the link to home.
  - put the logo on the website, in source form, so people can put it on
    stickers directly, etc.
  - put the source image for the stickers on the website, so people can
    print their own
R - make a page with the hidden service diagrams.
  - ask Jan to be the translation coordinator? add to volunteer page.
  - add a page for localizing all tor's components.
  - It would be neat if we had a single place that described _all_ the
    tor-related tools you can use, and what they give you, and how well they
    work.  Right now, we don't give a lot of guidance wrt
    torbutton/foxproxy/privoxy/polipo in any consistent place.