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

0.0.9pre4:
   o Don't use FascistFirewall if you're going via Tor, or if
     you're going via HttpProxy.
   o make RecommendedVersions a CONFIG_TYPE_LINELIST option
   o node 'groups' that are known to be in the same zone of control.
   o Nodes can list their coadministrated nodes.
   o If A lists B, it only counts if B also lists A
   o Users can list other coadministrated nodes if they like.
   o Never choose two coadministrated nodes in the same circuit.
   o let tor servers use proxies for port 80 exits
   o Use generic port redirector for IP/bits:Port->IP:Port .
   o Make use of them when we're doing exit connections.
   X We should set things in options to NULL, not rely on memset(...0)
     being equivalent.
   o We should check for memset(0) setting things to NULL with
     autoconf, and then rely on it in the code.

0.0.9pre5/6:
   o Replace running-routers with a router-status line that can be used
     without a list of router descriptors.
   o Add a log handler that sends stuff to syslog.
   o Deprecate unofficial configuration abbrevs; make official abbrevs
     only official on the command line.
   - per-month byte allowances.
N  - 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.
R  - Hibernate means "stop accepting connections, and start sleeping"
     Implement hibernation.  Have a separate
     about-to-start-hibernating state implemented in similar way to
     will shut-down-in-30-seconds state.
   - Rendezvous service bug: can we nail it down?
R  . bandwidth buckets for write as well as read.
N  - Make watchdogged clients check cached-directory mtime to avoid
     fetching directory in a tight loop.
   - Implement If-Modified-Since for directories.
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  - Pure C tor_resolve
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?
N&R  - Update Spec
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)
   - 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).
   D nt services on win32.
   - Once we have a trusted directory on port 80, stop falling back to
     forbidden ports when fascistfirewall blocks all good dirservers.

   0.0.9 and beyond:
   - 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)
   - make loglevel info less noisy
   - Facility to automatically choose long-term helper nodes; perhaps
     on by default for hidden services.
   - 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.
   - 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.
   - 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.
   - Support egd or other non-OS-integrated strong entropy sources

   more features, complex:
   - password protection for on-disk identity key
   . Switch dirservers entries to config lines:
     o read in and parse each TrustedDir config line.
     o stop reading dirservers file.
     o add some default TrustedDir lines if none defined, or if
       no torrc.
     o remove notion of ->is_trusted_dir from the routerlist. that's
       no longer where you look.
       o clean up router parsing flow, since it's simpler now?
     o 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.
     o when fetching a directory, if you want a trusted one,
       choose from the trusteddir list.
       o 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, and a basic GUI
     - and a basic gui
   - 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.

   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, including all needed libs.

   - 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
       o (need to not hardcode dirservers file in config.c)
       - Make tutorial reflect this.
     - 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.

N  . 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.