tor/doc/TODO

Legend:
SPEC!!  - Not specified
SPEC    - Spec not finalized
NICK    - nick claims
ARMA    - arma claims
        - Not done
        * Top priority
        . Partially done
        o Done
        D Deferred
        X Abandoned

For 0.0.9:
N&R- bring tor-spec up to date
N  . cache and serve running-routers on other nodes?
     . cache running-routers
     - download running-routers from servers running rc5-cvs or later
N  - pump up periods for fetching things; figure out how to do this
     backward-compatibily, so that people who did set dirfetchpostperiod
     get the right behavior.
N  - Adapt version parsing code to handle new version scheme; document new
     version scheme.
N&R. make loglevels info,debug less noisy
R  - fix dfc/weasel's intro point bug
R  - add goodell's .exit tld

Beyond 0.0.9:
   - server descriptor declares min log level, clients avoid servers
     that are too loggy.
N  - Clean up NT service code
N  - OS X package (and bundle?)
   - controller should have 'getinfo' command to query about rephist,
     about rendezvous status, etc.
   - allow transition from ORPort to !ORPort, and back
R  . bandwidth buckets for write as well as read.
   - Limit to 2 dir, 2 OR, N SOCKS connections per IP.
   - Implement If-Modified-Since for directories.
   - Make more configuration variables into CSVs.
N  - Handle rendezvousing with unverified nodes.
     - Specify: Stick rendezvous point's key in INTRODUCE cell.
       Bob should _always_ use key from INTRODUCE cell.
     - Implement.
R  - figure out enclaves, e.g. so we know what to recommend that people
     do, and so running a tor server on your website is helpful.
     - Do enclaves for same IP only.
     - Resolve first, then if IP is an OR, connect to next guy.
N  . the user interface interface
     - Implement a trivial fun gui.
N  - add ipv6 support.
     - Spec issue: if a resolve returns an IP4 and an IP6 address,
       which to use?
N&R  - Update Spec
R  X learn from ben about his openssl-reinitialization-trick to
     rotate tls keys without making new connections.
   - Do something to prevent spurious EXTEND cells from making middleman
     nodes connect all over.  Rate-limit failed connections, perhaps?
   - 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.
   - have a pool of circuits available, cannibalize them
     for your purposes (e.g. rendezvous, etc).
   - Once we have a trusted directory on port 80, stop falling back to
     forbidden ports when fascistfirewall blocks all good dirservers.

   o fix sprintf's to snprintf's?
   . Make intro points and rendezvous points accept $KEYID in addition
     to nicknames.
           o Specify
           o Implement parsing
           - Generate new formats (Not till 007 is dead)
   - Facility to automatically choose long-term helper nodes; perhaps
     on by default for hidden services.
   o Make command-line strict about checking options; make only certain
     option prefixes work.
   - Rate-limit OR and directory connections overall and per-IP and
     maybe per subnet.
   D put expiry date on onion-key, so people don't keep trying
     old ones that they could know are expired?
     * Leave on todo list, see if pre3 onion fixes helped enough.
   D should the running-routers list put unverified routers at the
     end?
     * Cosmetic, don't do it yet.
   D make advertised_server_mode() ORs fetch dirs more often.
     * not necessary yet.
   D Add a notion of nickname->Pubkey binding that's not 'verification'
     * eventually, only when needed
   D ORs use uniquer default nicknames
     * Don't worry about this for now
   D Handle full buffers without totally borking
     * do this eventually, no rush.
   D if destination IP is running a tor node, extend a circuit there
     before sending begin.
     * don't do this for now. figure out how enclaves work. but do
       enclaves soon.
   - Support egd or other non-OS-integrated strong entropy sources

   more features, complex:
   - password protection for on-disk identity key
   - Have clients and dirservers preserve reputation info over
     reboots.
     * continue not doing until we have something we need to preserve
   - round detected bandwidth up to nearest 10KB?
   - client software not upload descriptor until:
     - you've been running for an hour
     - it's sufficiently satisfied with its bandwidth
     - it decides it is reachable
     - start counting again if your IP ever changes.
     - never regenerate identity keys, for now.
     - you can set a bit for not-being-an-OR.
     * no need to do this yet. few people define their ORPort.
   - authdirserver lists you as running iff:
     - he can connect to you
     - he has successfully extended to you
     - you have sufficient mean-time-between-failures
     * keep doing nothing for now.
   - Include HTTP status messages in logging (see parse_http_response).

   blue sky:
   - Possible to get autoconf to easily install things into ~/.tor?

   ongoing:
   . rename/rearrange functions for what file they're in
   - generalize our transport: add transport.c in preparation for
     http, airhook, etc transport.
   o investigate sctp for alternate transport.

For September:
N    . Windows port
     o works as client
       - deal with pollhup / reached_eof on all platforms
     . robust as a client
     . works as server
       - can be configured
     - robust as a server
     . Usable as NT service
     - docs for building in win
     o installer, including all needed libs.
       - and including privoxy
       - and including a sockscap equivalent

   - Docs
     . FAQ
     - a howto tutorial with examples
       * put a stub on the wiki
     o tutorial: how to set up your own tor network
       o (need to not hardcode dirservers file in config.c)
       o Make tutorial reflect this.
     . port forwarding howto for ipchains, etc
     . correct, update, polish spec
     - document the exposed function api?
     - Document where we differ from tor-design

   . packages
     . find a long-term rpm maintainer

   - code
     - better warn/info messages
     - write howto for setting up tsocks, socat.
       - including on osx and win32
     - freecap handling
     - tsocks
       o gather patches, submit to maintainer
         * send him a reminder mail and see what's up.
       - intercept gethostbyname and others
         * add this to tsocks
       o do resolve via tor
     - redesign and thorough code revamp, with particular eye toward:
       - support half-open tcp connections
       - conn key rotation
       - other transports -- http, airhook
       - modular introduction mechanism
       - allow non-clique topology

Other details and small and hard things:
   - tor should be able to have a pool of outgoing IP addresses
     that it is able to rotate through. (maybe)
   - tie into squid
   - hidserv offerers shouldn't need to define a SocksPort
     * figure out what breaks for this, and do it.
   - when the client fails to pick an intro point for a hidserv,
     it should refetch the hidserv desc.
   . should maybe make clients exit(1) when bad things happen?
     e.g. clock skew.
   - should retry exitpolicy end streams even if the end cell didn't
     resolve the address for you
   o Make logs handle it better when writing to them fails.
   o Dirserver shouldn't put you in running-routers list if you haven't
     uploaded a descriptor recently
   . Refactor: add own routerinfo to routerlist.  Right now, only
     router_get_by_nickname knows about 'this router', as a hack to
     get circuit_launch_new to do the right thing.
   . Scrubbing proxies
           - Find an smtp proxy?
           . Get socks4a support into Mozilla
   - Need a relay teardown cell, separate from one-way ends.
   - Make it harder to circumvent bandwidth caps: look at number of bytes
     sent across sockets, not number sent inside TLS stream.
   - fix router_get_by_* functions so they can get ourselves too,
     and audit everything to make sure rend and intro points are
     just as likely to be us as not.

***************************Future tasks:****************************

Rendezvous and hidden services:
  make it fast:
    - preemptively build and start rendezvous circs.
    - preemptively build n-1 hops of intro circs?
    - cannibalize general circs?
  make it reliable:
    - standby/hotswap/redundant services.
    - store stuff to disk? dirservers forget service descriptors when
      they restart; nodes offering hidden services forget their chosen
      intro points when they restart.
  make it robust:
    - auth mechanisms to let midpoint and bob selectively choose
      connection requests.
  make it scalable:
    - right now the hidserv store/lookup system is run by the dirservers;
      this won't scale.

Tor scalability:
  Relax clique assumptions.
  Redesign how directories are handled.
    o Separate running-routers lookup from descriptor list lookup.
    - Resolve directory agreement somehow.
    o Cache directory on all servers.
  Find and remove bottlenecks
    - Address linear searches on e.g. circuit and connection lists.
  Reputation/memory system, so dirservers can measure people,
    and so other people can verify their measurements.
    - Need to measure via relay, so it's not distinguishable.
  Bandwidth-aware path selection. So people with T3's are picked
    more often than people with DSL.
  Reliability-aware node selection. So people who are stable are
    preferred for long-term circuits such as intro and rend circs,
    and general circs for irc, aim, ssh, etc.
  Let dissidents get to Tor servers via Tor users. ("Backbone model")

Anonymity improvements:
  Is abandoning the circuit the only option when an extend fails, or
    can we do something without impacting anonymity too much?
  Is exiting from the middle of the circuit always a bad idea?
  Helper nodes. Decide how to use them to improve safety.
  DNS resolution: need to make tor support resolve requests. Need to write
    a script and an interface (including an extension to the socks
    protocol) so we can ask it to do resolve requests. Need to patch
    tsocks to intercept gethostbyname, else we'll continue leaking it.
  Improve path selection algorithms based on routing-zones paper. Be sure
    to start and end circuits in different ASs. Ideally, consider AS of
    source and destination -- maybe even enter and exit via nearby AS.
  Intermediate model, with some delays and mixing.
  Add defensive dropping regime?

Make it more correct:
  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.
  Support IPv6.

Efficiency/speed/robustness:
  Congestion control. Is our current design sufficient once we have heavy
    use? Need to measure and tweak, or maybe overhaul.
  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.
  Use cpuworker for more heavy lifting.
    - Signing (and verifying) hidserv descriptors
    - Signing (and verifying) intro/rend requests
    - Signing (and verifying) router descriptors
    - Signing (and verifying) directories
    - Doing TLS handshake (this is very hard to separate out, though)
  Buffer size pool: allocate a maximum size for all buffers, not
    a maximum size for each buffer. So we don't have to give up as
    quickly (and kill the thickpipe!) when there's congestion.
  Exit node caching: tie into squid or other caching web proxy.
  Other transport. HTTP, udp, rdp, airhook, etc. May have to do our own
    link crypto, unless we can bully openssl into it.

P2P Tor:
  Do all the scalability stuff above, first.
  Incentives to relay. Not so hard.
  Incentives to allow exit. Possibly quite hard.
  Sybil defenses without having a human bottleneck.
  How to gather random sample of nodes.
  How to handle nodelist recommendations.
  Consider incremental switches: a p2p tor with only 50 users has
    different anonymity properties than one with 10k users, and should
    be treated differently.