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

      0.0.9:
        o Fix OutboundBindAddress
        o Config defaults should be consistent with config file and no
          config file.
        o write instructions for port-forwarding directives or programs
          to let people run on ports 80 and 443 without needing to bind
          tor to them.
        o clean up all the comma-separated stuff (eg exit policies) into
          smartlists.
        o investigate sctp for alternate transport.
        o Document all undocumented options, or mark them as undocumented
          in the source.
R       . bandwidth buckets for write as well as read.
        . Cached-directory changes:
          o make clients store the cached-directory to disk,
          o and use it when they startup, so they don't need to bootstrap
            from the authdirservers every time they start.
          - also, once we've reduced authdirserver entries to config
            lines, we can have lines that list cacheddirservers too.
        . compress the directory.
          o Implement gzip/zlib wrappers
          o Compress directories as they're cached/generated
            o When requested, give a compressed directory.
            o Decompress incoming HTTP based on Content-Encoding
            - Once dirservers are running new code, make clients
              request compressed directories.  (Alternative: Switch
              to HTTP/1.1 and use Allowed-Encoding.  Is that really
              what we want?)
N       - switch dirservers entries to config lines.
N       - add three default dirplaces if we parse the whole torrc and
          no dirplaces are specified.
N       - allow yourself to build circuits immediately if you have a
          recent cached directory
N       - let tor clients use http proxies for dir fetching
          - have a config entry to specify where to go
N       - per-month byte allowances.
          - Based on bandwidth and per-month allowance, choose a
            window within month to be up.  Stay up until allowance is
            used.  Adjust next month's window based on outcome.  Hibernate
            when we're not up.
          - Hibernate means "stop accepting connections, and start sleeping"
N       - Handle rendezvousing with unverified nodes.
          - Specify: Stick rendezvous point's key in INTRODUCE cell.
            Bob should _always_ use key from INTRODUCE cell.
          - Implement.
N       - Bail out early if datadirectory is NULL.
N       - Pure C tor_resolve
N       - node 'groups' that are known to be in the same zone of control.
          - Nodes can list their coadministrated nodes.
          - Users can list other coadministrated nodes if they like.
          - Never choose two coadministrated nodes in the same circuit.
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       - let tor servers use http proxies for port 80 exits
          - For squid, privoxy, etc on exitconnections.
          - (Don't need full HTTP proxy support; assume Host: header
            is set correctly.)  Use generic port redirector for
            IP/bits:Port->IP:Port .
N       - the user interface interface
          - Skeleton only.
          - Implement parts along with trivial fun gui.
N       - add ipv6 support.
          - Spec issue: if a resolve returns an IP4 and an IP6 address,
            which to use?
R       - learn from ben about his openssl-reinitialization-trick to
          rotate tls keys without making new connections.
          - (Roger grabs Ben next time he sees him on IRC) 
        D nt services on win32.

      0.0.8:
        - fix sprintf's to snprintf's?
        o Make it work on win32 with no $home
                o Don't crash.
                o Put files someplace reasonable.
        o Why is the first entry of kill -USR1 a router with a 0 key?
        o Tors deal appropriately when a newly-verified router has the
          same nickname as another router they know about
        X put ip:port:keyhash in intro points, rendezvous points,
          and hidserv descriptors.
        . 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)
NICK    . unify similar config entries that need to be split. put them
          into a smartlist, and have things take a smartlist.

        - figure out what to do when somebody asks to extend to
          ip:port:differentkey
* reject it. assuming this is as dumb as it sounds.
        - make loglevel info less noisy

      bug fixes, might be handy:
        - the directory servers complain a lot about people using the
          old key. does 0.0.7 use dirservers before it's pulled down
          the directory?
        - 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.
        - should the running-routers list put unverified routers at the
          end?
* Cosmetic, don't do it yet.
        - make advertised_server_mode() ORs fetch dirs more often.
* not necessary yet.
        - Add a notion of nickname->Pubkey binding that's not 'verification'
* eventually, only when needed
        - ORs use uniquer default nicknames
* Don't worry about this for now
        - Handle full buffers without totally borking
* do this eventually, no rush.

      more features, easy:
        - per-month byte allowances
* nick will spec something.
        - have a pool of circuits available, cannibalize them
          for your purposes (e.g. rendezvous, etc).
* hold off on that.
        - node 'groups' that are known to be in the same zone of control
* nick and roger will talk about it
        - do resolve before trying to attach the stream
* don't do this for now.
        - 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.
        - Track max ten-second b/w ever seen, to show operator

      more features, complex:
        - compress the directory. client sends http header
          "accept-transfer-encoding: gzip", server might send http header
          "transfer-encoding: gzip". ta-da.
          - grow a zlib dependency. keep a cached compressed directory.
* nick will look into this. not critical priority.
        - Switch dirservers entries to config lines:
          - read in and parse each TrustedDir config line.
          - stop reading dirservers file.
          - add some default TrustedDir lines if none defined, or if
            no torrc.
          - remove notion of ->is_trusted_dir from the routerlist. that's
            no longer where you look.
            - clean up router parsing flow, since it's simpler now?
          - when checking signature on a directory, look it up in
            options.TrustedDirs, and make sure there's a descriptor
            with that nickname, whose key hashes to the fingerprint,
            and who correctly signed the directory.
* nick will do the above
          - when fetching a directory, if you want a trusted one,
            choose from the trusteddir list.
            - which means keeping track of which ones are "up"
          - if you don't need a trusted one, choose from the routerinfo
            list if you have one, else from the trusteddir list.
* roger will do the above
        - add a listener for a ui
* nick chats with weasel
          - and a basic gui
        - Have clients and dirservers preserve reputation info over
          reboots.
* continue not doing until we have something we need to preserve
        - users can set their bandwidth, or we auto-detect it:
          - advertised bandwidth defaults to 10KB
          o advertised bandwidth is the min of max seen in each direction
            in the past N seconds.
            o calculate this
          o not counting "local" connections
          - 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.

      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.
NICK    - investigate sctp for alternate transport.

For September:
NICK    . 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
          - installer

        - Docs
          . FAQ
          o overview of tor. how does it work, what's it do, pros and
            cons of using it, why should I use it, etc.
          - a howto tutorial with examples
* put a stub on the wiki
          o tutorial: how to set up your own tor network
            - (need to not hardcode dirservers file in config.c)
* this will be solved when we put dirservers in config lines
          - port forwarding howto for ipchains, etc
* roger add to wiki of requests
          . correct, update, polish spec
          - document the exposed function api?
          o document what we mean by socks.

NICK    . packages
          . rpm
* nick will look at the spec file
          - find a long-term rpm maintainer
* roger will start guilting people

        - code
          - better warn/info messages
          o let tor do resolves.
          o extend socks4 to do resolves?
          o make script to ask tor for resolves
          - 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
        . 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.
    - Separate running-routers lookup from descriptor list lookup.
    - Resolve directory agreement somehow.
    - 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.