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

Documentation and testing on 0.1.2.x-final series

N - 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.

NR. Write 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.
N   - we should add a preamble to tor-design saying it's out of date.
N   . Document transport and natdport
      o In man page
      - In a good HOWTO.

    - Update dir-spec with decisions made on these issues:

        o clients don't log as loudly when they receive them
        o they don't count toward the 3-strikes rule
          D But eventually, we give up after getting a lot of 503s.
          D Delay when we get a lot of 503s, rather than punting onto the
            servers that have given us 503s?
          o Add a 'BadDirectory' flag to statuses.
        o authorities should *never* 503 a cache, and should never 503
          network status requests.
        D They can 503 client descriptor requests when they feel like it.
          How can they distinguish? Not implemented for now, maybe
          should abandon.
        - update dir-spec with what we decided for each of these

Things we'd like to do in 0.2.0.x:
  - Proposals:
    . 101: Voting on the Tor Directory System
      - Prepare ASAP for new voting formats
        - Don't flip out with warnings when voting-related URLs are
          uploaded/downloaded.
      . Finalize proposal
        - Merge 101 and 103 and dir-spec.txt into a new dir-spec.txt; fork
          the existing one into dir-spec-v2.txt.
      - Get authorities voting
        . Implement parsing for new document formats
          o Parse key certificates
          - Parse votes and consensuses
          - Unit tests for above
        - Code to manage key certificates
          - Cache on disk
          - Download as needed
          - Serve list as needed.
          - Avoid double-checking signatures every time we get a vote.
        - Code to generate votes
        - Code to generate consensus from a list of votes
        - Add a signature to a consensus.
        - Code to check signatures on a consensus
        - Push/pull documents as appropriate.
      - Start caching consensus documents once authorities make them
      - Start downloading and using consensus documents once caches serve them
    . 104: Long and Short Router Descriptors (by Jun 1)
      . Finalize proposal
      o Implement parsing for extra-info documents
      o Have routers generate extra-info documents.
      o Have have authorities accept them and serve them from specified URLs
        o Implement directory-protocol side.
        o Implement storage in memory
        o Implement cache on disk.
      o Have routers upload extra-info documents to authorities running
        version 0.2.0.0-alpha-dev (r10070) or later.
        o Implement, but make it option-controlled.
        o Make it always-on once it seems to work.
      - Implement option to download and cache extra-info documents.
      - Drop bandwidth history from router-descriptors
    - 105: Version negotiation for the Tor protocol (finalize by Jun 1)
    - 108: Base "Stable" Flag on Mean Time Between Failures
    - 109: No more than one server per IP address
    - 103: Splitting identity key from regularly used signing key
      - Merge with 101 into a new dir-spec.txt
    - 113: Simplifying directory authority administration
    - 110: prevent infinite-length circuits (phase one)
      - servers should recognize relay_extend cells and pass them
        on just like relay cells
  - Refactoring:
    - Make resolves no longer use edge_connection_t unless they are actually
      _on_ 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.
      O Implement cell queues
      o Keep doubly-linked list of active circuits on each or_conn.
      o Put all relay data on the circuit cell queue, not on the outbuf.
      o Don't move them into the target conn until there is space on the
        target conn's outbuf.
      o When making a circuit active on a connection with an empty buf,
        we need to "prime" the buffer, so that we can trigger the "I flushed
        some" test.
      X Change how directory-bridge-choking works: choke when circuit queue
        is full, not when the orconn is "too full".
        [No need to do this: the edge-connection choking will already take
        care of this a bit, and rewriting the 'bridged connection' code
        to not use socketpairs will give us even more control.]
      . Do we switch to pool-allocation for cells?
        o Implement pool-allocation
        o Have Tor use it for packed cells.
        o Document it.
        o Do something smart with freeing unused chunks.
        - Benchmark pool-allocation vs straightforward malloc.
        - Adjust memory allocation logic in pools to favor a little less
          slack memory.
      D Can we stop doing so many memcpys on cells?
      o Also, only package data from exitconns when there is space on the
        target OR conn's outbuf?  or when the circuit is not too full.
      - MAYBE kill stalled circuits rather than stalled connections; consider
        anonymity implications.
    - 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.)
      o Design
        o Pick a term.  The term is now "linked connection."
        o Figure out how to ensure that handle_read is always called.
          (Use event_active; keep active events in a list; use event_once
          to make sure that we call the event base dispatch function enough.)
      . Implement
        o Count connections and sockets separately
        . Allow connections with s == -1
        o Add a linked_conn field; it should get marked when we're marked.
        o Add a function to move bytes from buffer to buffer.
        o Have read_to_buf dtrt for linked connections
        o Have handle_read dtrt for linked connections
        o Have an activate/deactivate_linked_connection function.
        o Have activated connections added to a list on first activation, and
          that list made active before calls to event_loop.
        o Have connections get deactivated when no more data to write on
          linked conn outbuf.
        o Handle closing connections properly.
        o Actually create and use linked connections.
        - Handle rate-limiting on directory writes to linked directory
          connections in a more sensible manner.
        o Rename want_to_read and want_to_write; they're actually about
          being blocked, not about wanting to read/write.
        - 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.
    - Implement TLS shutdown properly when possible.
    - Maybe move NT services into their own module.
    . Autoconf cleanups and improvements:
      o Remove redundant event.h check.
      o Check for zlib with the same machinery as for libevent and openssl.
      o Make the "no longer strictly accurate" message accurate.
      . Tell the user what -dev package to install based on OS.
      - Detect correct version of libraries.
      o Run autoupdate
    - Refactor networkstatus generation:
      - Use networkstatus_getinfo_helper_single() as base of
        networkstatus generation; eliminate duplicate code.
      - Include "v" line in getinfo values.
  - Features:
    - Traffic priorities (by Jun 1)
      - Ability to prioritize own traffic over relayed traffic.
    - Implement a DNS proxy
    - Add a way to request DNS resolves from the controller.
    - A better UI for authority ops.
      - Follow weasel's proposal, crossed with mixminion dir config format
      - Write a proposal
    - Bridges users (rudimentary version) (By Jun 1)
      - Ability to specify bridges manually
      D 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.
      - Config option 'UseBridges' that bridge users can turn on.
        - uses bridges as first hop rather than entry guards.
      D Do we want to maintain our own set of entryguards that we use
        after the bridge? Open research question; let's say no for 0.2.0
        unless we learn otherwise.
      - Ask all directory questions to bridge via BEGIN_DIR.
    - Bridges operators (rudimentary version) (By Jun 1)
      - Ability to act as dir cache without a dir port.
      - Bridges publish to bridge authorities
      - 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.
    - Bridges authorities (rudimentary version) (By Jun 1)
      - Rudimentary "do not publish networkstatus" option for bridge
        authorities.
      - Clients can ask bridge authorities for more bridges.
    - Bridges (not necessarily by Jun 1)
      - Clients can ask bridge authorities for updates on known bridges.
      - More TLS normalization work: make Tor less easily
        fingerprinted. (Researched by Jun 1)
      - Directory system improvements
        - config option to publish what ports you listen on, beyond
          ORPort/DirPort.  It should support ranges and bit prefixes (?) too.
    - Let controller set router flags for authority to transmit, and for
      client to use.
    - Support relaying streams to ipv6.
    - Let servers decide to support BEGIN_DIR but not DirPort.
    - Tor should bind its ports before dropping privs, so users don't
      have to do the ipchains dance.
    - Blocking-resistance.
    - It would be potentially helpful to https requests on the OR port by
      acting like an HTTPS server.
    - 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.
  o Deprecations:
    o Remove v0 control protocol.
    - can we deprecate 'getinfo network-status'?
P - Packaging:
P   - Can we switch to polipo? (Jun 1)
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 0.9.8d "make test" fails at sha256t test.
  - add an AuthDirBadexit torrc option if we decide we want one.

Deferred from 0.1.2.x:
  - 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.
  - 'networkstatus arrived' event
  - More work on AvoidDiskWrites?
  - Get some kind of "meta signing key" to be used solely to sign
    releases/to certify releases when signed by the right people/
    to certify sign the right people's keys?  Also use this to cert the SSL
    key, etc. (Proposal 103)
  - 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.
    - Save and mmap v1 directories, and networkstatus docs; store them
      zipped, not uncompressed.
      - Switch cached_router_t to use mmap.
      - 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?)
      - What do we do about the fact that people can't read zlib-
        compressed files manually?

  - 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.

  X Eventdns improvements
    X Have a way to query for AAAA and A records simultaneously.
    X Improve request API: At the very least, add the ability to construct
      a more-or-less arbitrary request and get a response.
    X (Can we suppress cnames? Should we?)

  - 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.
M   - 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.
  o Unify autoconf search code for libevent and openssl.  Make code
    suggest platform-appropriate "devel" / "dev" / whatever packages
    if we can link but we can't find the headers.
  - 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.
  - 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.
R - 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.
  o When we export something from foo.c file for testing purposes only,
    make a foo_test.h file for test.c to include... or put them behind an
    #ifdef FOO_PRIVATE.
  - 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.
  - 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


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.
  - 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.
  o Include the output of svn info in the binary, so it's trivial to see what
    version a binary was built from.
    o Do the same for svk info.
  - 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.
    - 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.
  - 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.
  - 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.
  - 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?
  o tor-resolve script should use socks5 to get better error messages.
  - hidserv offerers shouldn't need to define a SocksPort
    * figure out what breaks for this, and do it.
  - tor should be able to have a pool of outgoing IP addresses
    that it is able to rotate through. (maybe)
    - Specify; implement.
  - 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.
  - Robust decentralized storage for hidden service descriptors.
  - The "China problem"
  - 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 - evaluate Tor under CentOS5/RHES5
P - figure out selinux policy for tor
P - make the nsis mingw packaging scripts fail if it tries to parse

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.