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

    X <nickm> "Let's try to find a way to make it run and make the version
       match, but if not, let's just make it run."
    X <arma> "should we detect if we have a --with-ssl-dir and try the -R
      by default, if it works?"

Items for 0.1.2.x, real soon now:
? - Bug: combination of things:
    When we've been idle a long time, we stop fetching server
    descriptors. When we then get a socks request, we build circuits
    immediately using whatever descriptors we have, rather than waiting
    until we've fetched correct ones.

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.
  o Stop recommending exits as guards?
    look at the overall fraction of exits in the network. if the
    fraction is too small, none of them get to be guards.

R - Reconstruct ChangeLog; put rolled-up info in ReleaseNotes or something.

Items for 0.1.2.x:
  - enumerate events of important things that occur in tor, so vidalia can
    react.
    o Backend implementation
R   - Actually list all the events (notice and warn log messages are a good
      place to look.)  Divide messages into categories, perhaps.
R   - Specify general event system
R   - Specify actual events.
R   - and implement the rest

  . Have (and document) a BEGIN_DIR relay cell that means "Connect to your
    directory port."
    o Specify
    o Implement
    o Use for something, so we can be sure it works.
    o Test and debug
R   - turn the received socks addr:port into a digest for setting .exit
    - be able to connect without having a server descriptor, to bootstrap.
R     - handle connect-dir streams that don't have a chosen_exit_name set.
      o include ORPort in DirServers lines so we can know where to connect.
        list the orport as 0 if it can't handle begin_dir.
      o List versions in status page
        o A new line in the status entry. "Tor 0.1.2.2-alpha". If it's
          a version, treat it like one. If it's something else, assume
          it's at least 0.1.2.x.
        D maybe we could have it be a new 'v' line in the status, with
          key=value syntax. so we could have a 'tor' version, but we
          could also have a 'conn' version, a 'dir' version, etc down
          the road. and one day maybe the 'tor' key would be deprecated.

  o Document .noconnect addresses...
    A new file 'address-spec.txt' that describes .exit, .onion,
    .noconnect, etc?

  - Servers are easy to setup and run: being a relay is about as easy as
    being a client.
    . Reduce resource load
      o A way to alert controller when router flags change.
        o Specify: SETEVENTS NS
        o Implement
R       - Hunt for places that change networkstatus info that I might have
          missed.
R     . option to dl directory info via tor
        o Make an option like __AllDirActionsPrivate that falls back to
          non-Tor DL when not enough info present.  (TunnelDirConns).
        - Set default to 0 before release candidate.
        - Think harder about whether TunnelDirConns should be on
          by default.
        - Handle case where we have no descriptors and so don't know who can
          handle BEGIN_DIR.

N - DNS improvements
    o Don't ask reject *:* nodes for DNS unless client wants you to.
    . Asynchronous DNS
      - Make evdns use windows strerror equivalents.
      - Make sure patches get into libevent.
      - Verify that it works well on windows
    . Make reverse DNS work.
      . Add client-side interface
        o SOCKS interface: specify
        o SOCKS interface: implement
d       - Cache answers client-side
        o Add to Tor-resolve.py
        - Add to tor-resolve
d   - Be a DNS proxy.
    o Check for invalid characters in hostnames before trying to resolve
      them.  (This will help catch attempts do to mean things to our DNS
      server, and bad software that tries to do DNS lookups on whole URLs.)
      o address_is_invalid_destination() is the right thing to call here
        (and feel free to make that function smarter)
      o add a config option to turn it off.
      - and a man page for that option
    - Bug 364: notice when all the DNS requests we get back (including a few
      well-known sites) are all going to the same place.
    o Bug 363: Warn and die if we can't find a nameserver and we're running a
      server; don't fall back to 127.0.0.1.
?   - maybe re-check dns when we change IP addresses, rather than
      every 12 hours?
    - Bug 326: Give fewer error messages from nameservers. 
      - Only warn when _all_ nameservers are down; otherwise info.
      - Increase timeout; what's industry standard?
        - Alternatively, raise timeout when nameserver dies but comes back
          quickly?
      - Don't believe that our sole nameserver is dead?  or, not until more
        failures than it would take to think one of several nameservers was
        dead?
      - Possibly, don't warn until second retry of a nameserver gets no
        answer?
      - warn if all of your nameservers go down and stay down for like
        5 minutes.
R o Take out the '5 second' timeout from the socks detach schedule.

  - Performance improvements

  - Critical but minor bugs, backport candidates.
    - support dir 503s better
      o clients don't log as loudly when they receive them
N     - they don't count toward the 3-strikes rule
        - should there be some threshold of 503's after which we give up?
        - Delay when we get a lot of 503s?
      o split "router is down" from "dirport shouldn't be tried for a while"?
        We want a field to hold "when did we last get a 503 from this
        directory server."  Probably, it should go in local_routerstatus_t,
        not in routerinfo_t, since we can try to use servers as directories
        before we have their descriptors.  Possibly, it should also go in
        trusted_dir_server_t.
        o Add a last_dir_503_at field.
        o Have it get updated correctly.
        o Prefer to use directories that haven't given us a 503 for the last
          60 minutes.
      - authorities should *never* 503 a cache, and should never 503
        network status requests. They can 503 client descriptor requests
        when they feel like it.
      - update dir-spec with what we decided for each of these


  o Have a mode that doesn't write to disk much, so we can run Tor on
    flash memory (e.g. Linksys routers or USB keys).
    o Add AvoidDiskWrites config option.
    o only write state file when it's "changed"
      o crank up the numbers if avoiddiskwrites is on.
      D some things may not want to get written at all.
    o stop writing fingerprint every restart
    D more?

NR. Write path-spec.txt

  - Packaging
    - Tell people about OSX Uninstaller
    - Quietly document NT Service options
    - Switch canonical win32 compiler to mingw.
NR  D 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.
    - If we haven't replaced privoxy, lock down its configuration in all
      packages, as documented in tor-doc-unix.html
    o script to look at config.c, torrc.sample, tor.1.in, to tell us
      what's missing in which and notice which descriptions are missing.

  - Docs
    - More prominently, we should have a recommended apps list.
      - recommend gaim.
      - unrecommend IE because of ftp:// bug.
    - torrc.complete.in needs attention?
    - we should add a preamble to tor-design saying it's out of date.

  - Improvements to bandwidth counting
R   - look into "uncounting" bytes spent on local connections, so
      we can bandwidthrate but still have fast downloads.
R   - "bandwidth classes", for incoming vs initiated-here conns,
      and to give dir conns lower priority.
    . Write limiting; separate token bucket for write
      o preemptively give a 503 to some v1 dir requests
      - preemptively give a 503 to some v2 dir requests
      - per-conn write buckets
      - separate config options for read vs write limiting

  - Forward compatibility fixes
    o Stop requiring "opt" to ignore options in descriptors, networkstatuses,
      and so on.
    - Caches should start trying to cache consensus docs?
    - Start uploading short and long descriptors; authorities should support
      URLs to retrieve long descriptors, and should discard short descriptors
      for now.  Later, once tools use the "long descriptor" URLs, authorities
      will serve the short descriptors every time they're asked for
      a descriptor.

Topics to think about during 0.1.2.x development:
  * Figure out incentives.
    - (How can we make this tolerant of a bad v0?)
  * Figure out non-clique.
  * Figure out China.
  - Figure out partial network knowledge.
  - Figure out hidden services.
  - Design next-version protocol for directories
  - Design next-version protocol for connections

For blocking-resistance scheme:
  o allow ordinary-looking ssl for dir connections. need a new dirport
    for this, or can we handle both ssl and non-ssl, or should we
    entirely switch to ssl in certain cases?
  D need to figure out how to fetch status of a few servers from the BDA
    without fetching all statuses. A new URL to fetch I presume?

Deferred from 0.1.2.x:
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.
  - 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?

  - Refactor DNS resolve implementation
    - Refactor exit side of resolve: do we need a connection_t?
    - Refactor entry side of resolve: do we need a connection_t?

  - 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.

  - A more efficient dir protocol.
    - Authorities should fetch the network-statuses amongst each
      other, consensus them, and advertise a communal network-status.
      This is not so much for safety/complexity as it is to reduce
      bandwidth requirements for Alice.
      - How does this interact with our goal of being able to choose
        your own dir authorities? I guess we're now assuming that all
        dir authorities know all the other authorities in their "group"?
    - Should we also look into a "delta since last network-status
      checkpoint" scheme, to reduce overhead further?
    - Extend the "r" line in network-status to give a set of buckets (say,
      comma-separated) for that router.
      - Buckets are deterministic based on IP address.
      - Then clients can choose a bucket (or set of buckets) to
        download and use.

  - Improvements to versioning.
    - When we connect to a Tor server, it sends back a cell listing
      the IP it believes it is using. Use this to block dvorak's attack.
      Also, this is a fine time to say what time you think it is.
      o Verify that a new cell type is okay with deployed codebase
      . Specify HELLO cells
      . Figure out v0 compatibility.
      - Implement

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

  - Simplify authority operation
    - Follow weasel's proposal, crossed with mixminion dir config format

  - A way to adjust router flags from the controller.
    (How do we prevent the authority from clobbering them soon after?)
  - a way to pick entry guards based wholly on extend_info equivalent;
    a way to export extend_info equivalent.

  - Count TLS bandwidth more accurately

  - 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

  - Failed rend desc fetches sometimes don't get retried. True/false?

  - 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.

Minor items for 0.1.2.x as time permits:
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.
  D don't do dns hijacking tests if we're reject *:* exit policy?
    (deferred until 0.1.1.x is less common)
  - When we export something from foo.c file for testing purposes only,
    make a foo_test.h file for test.c to include.
  - 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
  o even if your torrc lists yourself in your myfamily line, don't list it in
    the descriptor.
  . Flesh out options_description array in src/or/config.c
  - Don't let 'newnym' be triggered more often than every n seconds.
  o change log_fn() to log() on notice/warn/err logs where we can.
  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.")
! - Tor should bind its ports before dropping privs, so users don't
    have to do the ipchains dance.
  - 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.
  o The bw_accounting file should get merged into the state file.
  - Streamline how we pick entry nodes: Make choose_random_entry() have
    less magic and less control logic.
  - 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.
  - Display the reasons in 'destroy' and 'truncated' cells under some
    circumstances?
  - We need a way for the authorities to declare that nodes are
    in a family.  Also, it kinda sucks that family declarations use O(N^2)
    space in the descriptors.
  - 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
    X kill dns workers more slowly
  . 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

  - 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.
      - It would be nice to request address lookups from the controller
        without using SOCKS.
      - Make everything work with hidden services
  - Directory system improvements
    - config option to publish what ports you listen on, beyond
      ORPort/DirPort.  It should support ranges and bit prefixes (?) too.
      - Parse this.
      - Relay this in networkstatus.

Future version:
  - Configuration format really wants sections.
  - Good RBL substitute.
  - 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?
  - 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?
  - Stop using tor_socketpair to make connection bridges: do an
    implementation that uses buffers only.

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

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.
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.