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 Deferred
        X Abandoned

    . <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."
    - <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:
  - Bug: We are willing to build circuits using not-up-to-date descriptors,
    when we get a request and we've been idle a long time.
  - 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.
  - Servers are easy to setup and run: being a relay is about as easy as
    being a client.
    - Reduce resource load
      - look into "uncounting" bytes spent on local connections. so
        we can bandwidthrate but still have fast downloads.
      - Write limiting; separate token bucket for write
      o dir answers include a your-ip-address-is header, so we can
        break our dependency on dyndns.
      - Count TLS bandwidth more accurately
      - Write-limit directory responses.
N   . Improve memory usage on tight-memory machines.
      - Directory-related fixes.
        o Remember offset and location of each descriptor in the cache/journal
        o When sending a big pile of descs to a client, don't shove them all
          on the buffer at once. Keep a list of the descriptor digests for
          the descriptors we still want to send.  We might end up truncating
          some replies by returning fewer descriptors than were requested (if
          somebody requests a desc that we throw away before we deliver it),
          but this happens only when somebody wants an obsolete desc, and
          clients can already handle truncated replies.
        o But what do we do about compression? That's the part that makes
          stuff hard.
          o Implement compress/decompress-on-the-fly support.
          o Use it for returning lists of descriptors.
          o Use it for returning lists of network status docs. (This will
            take a hybrid approach; let's get the other bits working first.)
          o Make clients handle missing Content-Length tags.  (Oh, they do.)
            o Verify that this has happened for a long time.
        o Try a similar trick for spooling out v1 directories.  These we
          _uncompress_ on the fly.
        - Look into pulling serverdescs off buffers as they arrive.
        . Mmap cache files where possible.
          o Mmap cached-routers file; when building it, go oldest-to-newest.
          - More unit tests and asserts for cached-routers file: ensure digest
            for the right router.  Verify dl by digest, fp, etc.
          - Make sure cached-routers values and offsets are correct in the
            presence of windows FS insanity.
          - Save and mmap v1 directories; store them zipped, not uncompressed.
          - Store networkstatus docs zipped, not uncompressed.  Maaaybe mmap
            them too.
        - Be a little more OO to save memory in frequently
          replicated structs.
          o Split circuit_t into origin circuits and or circuits
            - Move as many fields as reasonable out of base class.
            - Re-pack structs to avoid wasted bytes.
          - Split connection_t based on type field.

    - "bandwidth classes", for incoming vs initiated-here conns.
    o Asynchronous DNS
      - and test it
      - make it the default on platforms where it works

  - Security improvements
    - Directory guards
R   - remember the last time we saw one of our entry guards labelled with
      the GUARD flag. If it's been too long, it is not suitable for use.
      If it's been really too long, remove it from the list.

  - Make reverse DNS work.

  - Performance improvements
    - 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.
    - Clients should prefer to avoid exit nodes for non-exit path positions.
      (bug 200)
    - Have a "Faster" status flag that means it. Fast2, Fast4, Fast8?

  - A more efficient dir protocol.
    - Clients stop dumping old descriptors if the network-statuses
      claim they're still valid.
      - Later, servers will stop generating new descriptors simply
        because 18 hours have passed.
    - 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.

  - Critical but minor bugs, backport candiates.
    - 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.
R   - Failed rend desc fetches sometimes don't get retried.
    . If we fail to connect via an exit enclave, (warn and) try again
      without demanding that exit node.
      - And recognize when extending to the enclave node is failing,
        so we can abandon then too.
R   - non-v1 authorities should not accept rend descs.
    - We need a separate list of "hidserv authorities" if we want to
      retire moria1 from the main list.
    - support dir 503s better
      o clients don't log as loudly when they receive them
      - they don't count toward the 3-strikes rule
        - should there be some threshold of 503's after which we give up?
      - think about how to split "router is down" from "dirport shouldn't
        be tried for a while"?
      - authorities should *never* 503 a cache, but *should* 503 clients
        when they feel like it.
      - update dir-spec with what we decided for each of these
    - provide no-cache no-index headers from the dirport?

  - 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

  - 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
    - Implement

N - Exitlist should avoid outputting the same IP address twice.

N - Write path-spec.txt
  - Break the dir v1 stuff out of tor-spec.txt into dir-spec-v1.txt,
    and change the new dir-spec.txt to dir-spec-v2.txt.

  - Packaging
    - Tell people about OSX Uninstaller
    - Quietly document NT Service options

  - Docs
    - More prominently, we should have a recommended apps list.
      - recommend gaim.
      - unrecommend IE because of ftp:// bug.
    - torrc.complete.in needs attention?

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 avoiding duplicate /24 lines
  - Figure out partial network knowledge.
  - Figure out hidden services.

Minor items for 0.1.2.x as time permits.
  - 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.
  - The bw_accounting file should get merged into the state file.
  - Streamline how we define a guard node as 'up'.
  - Better installers and build processes.
    - Commit edmanm's win32 makefile to tor cvs contrib, or write a new one.
  - 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.
  - rate limit the number of exit connections to a given destination, to
    help with DoS/crawling issues.
  - cpu fixes:
    - see if we should make use of truncate to retry
    - 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
      - 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:
  . 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)
  - let each hidden service (or other thing) specify its own
    OutboundBindAddress?
  - Have a mode that doesn't write to disk much, so we can run Tor on
    flash memory (e.g. Linksys routers).

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.
P - flesh out the rest of the section 6 of the faq
  . 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.

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.
  o track down the patch for cross-compiling.