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, real soon now:
x - 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.
x - 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.
N - when we start, remove any entryguards that are listed in excludenodes.
N - 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.
  . Figure out avoiding duplicate /24 lines
    o automatically add /16 servers to family
    D do it in an efficient way. keep a list of something somewhere?
      - The right thing here is to revamp our node selection implementation.
N   - make it configurable, so people can turn it on or off.
N - Clients stop dumping old descriptors if the network-statuses
    claim they're still valid.
R . 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.
N - We need a separate list of "hidserv authorities" if we want to
    retire moria1 from the main list.
P - Figure out why dll's compiled in mingw don't work right in Winxp.
P - Figure out why openssl 0.9.8c "make test" fails at sha256t test.

Items for 0.1.2.x:
  o re-enable blossom functionality: let tor servers decide if they
    will use local search when resolving, or not.
N   - Document it.
  - enumerate events of important things that occur in tor, so vidalia can
    react.
N   - Backend implementation
R   - Actually list all the events (notice and warn log messages are a good
      place to look.)  Divide messages into categories, perhaps.
N   - Specify general event system
R   - Specify actual events.

x - 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.

N - Simplify authority operation
    - Follow weasel's proposal, crossed with mixminion dir config format
    - Reject/invalidate by IP.

  - Servers are easy to setup and run: being a relay is about as easy as
    being a client.
    - Reduce resource load
N     - Come up with good 'nicknames' automatically, or make no-nickname
        routers workable. [Make a magic nickname "Unnamed" that can't be
        registered and can't be looked up by nickname.]
d     - Tolerate clock skew on bridge relays.
d     - A way to examine and twiddle router flags from controller.
      - A way to export server descriptors to controllers
N         - Event / getinfo for "when did routerdesc last change".
d     - a way to pick entries based wholly on extend_info equivalent;
        a way to export extend_info equivalent.
R     - option to dl directory info via tor
        - Make an option like __AllDirActionsPrivate that falls back to
          non-Tor DL when not enough info present.
      D Count TLS bandwidth more accurately

    - 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.
d     - Write limiting; separate token bucket for write
        - Write-limit directory responses (need to research)

N - DNS improvements
    o Option to deal with broken DNS of the "ggoogle.com? Ah, you meant
      ads.me.com!" variety.
      o Autodetect whether DNS is broken in this way.
    o Don't ask reject *:* nodes for DNS unless client wants you to.
    . Asynchronous DNS
      o Document and rename SearchDomains, ResolvConf options
      D Make API closer to getaddrinfo()
      - Teach it to be able to listen for A and PTR requests to be processed.
        Interface should be set_request_listener(sock, cb); [ cb(request) ]
        send_reply(request, answer);
d     - Add option to use /etc/hosts?
d     - Special-case localhost?
      - Verify that it works on windows
    . Make reverse DNS work.
      o Specify
      X Implement with dnsworkers
        (There's no point doing this, since we will throw away dnsworkers once
        eventdns is confirmed to work everywhere.)
      o Implement in eventdns
      o Connect to resolve cells, server-side.
      o Add element to routerinfo to note routers that aren't using eventdns,
        so we can avoid sending them reverse DNS etc.
      o Fix the bug with server-side caching, whatever is causing it.
      . Add client-side interface
        o SOCKS interface: specify
        o SOCKS interface: implement
        - Cache answers client-side
        o Add to Tor-resolve.py
        - Add to tor-resolve
    - 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.)
      - address_is_invalid_destination() is the right thing to call here
        (and feel free to make that function smarter)

  - Performance improvements

x   - 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)
R     - spec
x     - implement

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

  - A more efficient dir protocol.
N   - Later, servers will stop generating new descriptors simply
      because 18 hours have passed: we must start tolerating this now.

  - Critical but minor bugs, backport candidates.
d   - Failed rend desc fetches sometimes don't get retried. True/false?
R   - non-v1 authorities should not accept rend descs.
R   - 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?
        - Delay when we get a lot of 503s.
N     - split "router is down" from "dirport shouldn't be tried for a while"?
        Just a separate bit.
      - 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

N   - 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

  o Exitlist should avoid outputting the same IP address twice.

Nd- 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.
    - only write state file when it's "changed"
    - stop writing identity key / fingerprint / etc every restart
    - stop caching directory stuff -- and disable mmap?
    - more?

NR- Write path-spec.txt

  - Packaging
    - Tell people about OSX Uninstaller
    - Quietly document NT Service options
    - Switch canonical win32 compiler to mingw.
NR  - 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.

  - 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.

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:
  X 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?
Rd- Official way to do authenticated dir conns: connect to OR port,
    and exit to 'localhost:dir-port'.
    - Make everybody with a dir-port implicitly accept exit to
      localhost:dir-port.
    - Check whether this works with one-hop circ case.
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:
  - 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?

  - Add IPv6 support to eventdns.c

  - 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?

  - 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

Minor items for 0.1.2.x as time permits:
  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; sent controller event.
! - 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.
! - The bw_accounting file should get merged into the state file.
R - Streamline how we pick entry nodes.
! - Better installers and build processes.
    - Commit edmanm's win32 makefile to tor 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.
  - 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.
  o smartlist_uniq(): We have at least 3 places that check a smartlist for
    duplicates and then removes them: networkstatus_parse_from_string(),
    sort_version_list(), and router_rebuild_descriptor().  This should probably
    get its own function that takes a comparator and a delete function.

Future version:
  - Configuration format really wants sections.
  - Good RBL substitute.
  . 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?

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.

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.