tor/doc/TODO

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

Non-Coding, Soon:
  - FAQ entry: why gnutls is bad/not good for tor
P - flesh out the rest of the section 6 of the faq
P - gather pointers to livecd distros that include tor
  - put the logo on the website, in source form, so people can put it on
    stickers directly, etc.
  - more pictures from ren. he wants to describe the tor handshake, i want to
    talk about hidden services.
  * clean up the places where our docs are redundant (or worse, obsolete in
    one file and correct elsewhere). agl has a start on a global
    list-of-tor-docs.
P - update window's docs to clarify which versions of windows, and why a
    DOS window, how it's used, for the less technical users
NR- write a spec appendix for 'being nice with tor'
  - Hunt for open socks ports on tor servers, send mail
  - tor-in-the-media page
  - Ask schanzle@cas.homelinux.org about a patch for  rpm spec fixes against
    tor-0.1.0.7.rc
  - Remove need for HACKING file.


For 0.1.0.x:
  o Why do solaris cpuworks go dormant?
    (Apparently, disabling threads fixes this.)
  o Fix the remaining flyspray bugs marked for 0.1.0.9
  X Free remaining unfreed memory (arma will run valgrind)
    (Not for a stable release)
  o Note libevent/method/platform combos that are unlikely to work.
  X change torrc to point to abuse-faq (once abuse-faq is posted)
  . Memory use on Linux: what's happening?
    - Is it threading?  (Maybe, maybe not)
    - Is it the buf_shrink bug? (Quite possibly)
    - Instrument the 0.1.1 code to figure out where our memory is going;
      apply the results. (all platforms?)
  - Why does kevent barf with EINVAL on some freebsd boxes?
    - Submit libevent patch to Niels
    - Warn on non-repeated EINVAL in Tor (don't die.)
    - Investigate why freebsd kernel actually does this: it doesn't seem
      simple to trigger.

for 0.1.1.x:
  - switch accountingmax to count total in+out, not either in or
    out. it's easy to move in this direction (not risky), but hard to
    back, out if we decide we prefer it the way it already is. hm.
  . Come up with a coherent strategy for bandwidth buckets and TLS. (The
    logic for reading from TLS sockets is likely to overrun the bandwidth
    buckets under heavy load.  (Really, the logic was never right in the
    first place.)  Also, we should audit all users of get_pending_bytes().)
    - Make it harder to circumvent bandwidth caps: look at number of bytes
      sent across sockets, not number sent inside TLS stream.
  - Handle rendezvousing with unverified nodes.
    - Specify: Stick rendezvous point's key in INTRODUCE cell.
      Bob should _always_ use key from INTRODUCE cell.
    - Implement.
  - make sure err-level log events get flushed to the controller
    immediately, since tor will exit right after.
  - it looks like tor_assert writes to stderr. what happens if
    stderr was closed and is now something else? uh.
  - new controller protocol
    - Specify
    - Implement
  - controller should have an event to learn about new addressmappings,
    e.g. when we learn a hostname to IP mapping ?
  - 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
    - Implement
  - Destroy and truncated cells should have reasons.
  - Add private:* alias in exit policies to make it easier to ban all the
    fiddly little 192.168.foo addresses.
    (AGL had a patch; consider applying it.)
  - recommended-versions for client / server ?
  - warn if listening for SOCKS on public IP.
  - Forward-compatibility: add "needclientversion" option or "opt critical"
    prefix.
  - cpu fixes:
    - see if we should make use of truncate to retry
    - hardware accelerator support
r   - kill dns workers more slowly
  - continue decentralizing the directory
    - Specify and design all of the below before implementing any.
    - Figure out what to do about hidden service descriptors.
    M have two router descriptor formats
    - dirservers verify reachability claims
    - find 10 dirservers. (what are criteria to be a dirserver?)
    - some back-out mechanism?
      - dirservers have blacklist of IPs they hate
      - a way of rolling back approvals to before a timestamp
      - have new people be in limbo and need to demonstrate usefulness
        before we approve them
      - other?
    - dirservers publish router-status with all these flags.
    - Servers publish new descriptors when options change, when 12-24 hours
      have passed, when uptime is reset, or when bandwidth changes a lot.
    - alices fetch many router-statuses and update descriptors as needed.
    - add if-newer-than fetch options
    - dirservers allow people to lookup by N descriptors, or to fetch all.
    - alices avoid duplicate class C nodes.
    - everybody with a dirport will give you his descriptor.
    - config option, on by default, to cache all descriptors.
    - Compress router desc sets before transmitting them
    M Analyze how bad the partitioning is or isn't.
  - Naming:
    - Specify and design all of the below before implementing any.
    - some dirservers announce that they manage bindings (a flag in
      router-status).
    - other dirservers mention a binding if there is no conflict for
      that binding among the dirservers that manage it.
      no conflict == any of them bind it and no disagreement.
    - alice can specify a nickname and it will record that name in her
      datadir along with the key *if* it is bound. otherwise her specifying
      will fail (loudly we hope).
    - thus when a binding vanishes (e.g. conflict) alice will keep using
      the one she meant.
    - if the binding changes keys, the entry in her datadir will silently
      get corrected.
  - packaging and ui stuff:
    - multiple sample torrc files (tyranix?)
    - uninstallers
      . for os x
    - something, anything, for sys tray on Windows.
    - figure out how to make nt service stuff work?
      . Document it.
N   - Vet all pending installer patches
      - Win32 installer plus privoxy, sockscap/freecap, etc.
      - Vet win32 systray helper code
N  . Make logs go into platform default locations.
     o OSX
     - Windows. (?)

Reach (deferrable) items for 0.1.1.x:
  - Start using create-fast cells as clients
  - Let more config options (e.g. ORPort) change dynamically.
  - start handling server descriptors without a socksport?

For 0.1.1.x, if we can figure out how:
  - rewrite how libevent does select() on win32 so it's not so very slow.
  - helper nodes (at least preliminary)
  - enclaves (at least preliminary)
  - Write limiting; separate token bucket for write
  - 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?

Future version:
  - 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.
  - make min uptime a function of the available choices (say, choose 60th
    percentile, not 1 day.)
  - config option to publish what ports you listen on, beyond ORPort/DirPort
  - hidserv offerers shouldn't need to define a SocksPort
    * figure out what breaks for this, and do it.
  - auth mechanisms to let hidden service midpoint and responder filter
    connection requests.
  - Relax clique assumptions.
  - tor should be able to have a pool of outgoing IP addresses
    that it is able to rotate through. (maybe)

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.
  - Conn key rotation.
  - 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)

Volunteer projects:  [Phobos moves these to contribute.html]
  - use openssl aes when available
  - do the kernel buffer style design
  - Server instructions for OSX and Windows operators.
  - Improve and clarify the wiki entry on port forwarding.
  - how do ulimits work on win32, anyway?  (We should handle WSAENOBUFS as
    needed, look at the MaxConnections registry entry, look at the
    MaxUserPort entry, and look at the TcpTimedWaitDelay entry. We may also
    want to provide a way to set them as needed. See bug 98.)
  - Implement reverse DNS (already specified)
  - It would be nice to have a FirewalledIPs thing that works like
    FirewallPorts.
  - Make configure.in handle cross-compilation
    - Have NULL_REP_IS_ZERO_BYTES default to 1.
    - Make with-ssl-dir disable search for ssl.
  - Packaging, docs, etc:
   - Exit node caching: tie into squid or other caching web proxy.
  - Have clients and dirservers preserve reputation info over
    reboots.
  - Support egd or other non-OS-integrated strong entropy sources
  - password protection for on-disk identity key
  - Possible to get autoconf to easily install things into ~/.tor?
  - server descriptor declares min log level, clients avoid servers
     that are too loggy.
  - Separate node discovery from routing to allow neat extensions. [Goodell?]
    - Add SetServerStatus control event to adjust verified/running status of
      nodes.
    - Add NoDownload config option to prevent regular directory downloads
      from happening.
  - Choosing exit node by meta-data, e.g. country.
  - What info squeaks by Privoxy? Are other scrubbers better?
  - web proxy gateways to let normal people browse hidden services.
    (This has been done a few times, but nobody has sent us code.)
  - 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.
  - Congestion control. Is our current design sufficient once we have heavy
    use? Need to measure and tweak, or maybe overhaul.
  - Add alternative versions of crypto.c and tortls.c to use libnss or
    libgcrypt+gnutls.
  - If we have a trusted directory on port 80, optionally stop falling back
    to forbidden ports when fascistfirewall blocks all good dirservers.


Research projects: [Phobos moves these to contribute.html]
  - Arranging membership management for independence.
    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.
  - Incentives to relay; incentives to exit.
  - Allowing dissidents to relay through Tor clients.
  - Experiment with mid-latency systems. How do they impact usability,
    how do they impact safety?
  - Understand how powerful fingerprinting attacks are, and experiment
    with ways to foil them (long-range padding?).
  - Come up with practical approximations to picking entry and exit in
    different routing zones.
  - Find ideal churn rate for helper nodes; how safe is it?
  - Attacking freenet-gnunet/timing-delay-randomness-arguments.
  - Is exiting from the middle of the circuit always a bad idea?
  - IPv6 support (For exit addresses)
    - Spec issue: if a resolve returns an IP4 and an IP6 address,
      which to use?
    - Add to exit policy code
    - Make tor_gethostbyname into tor_getaddrinfo
    - Make everything that uses uint32_t as an IP address change to use
      a generalize address struct.
    - Change relay cell types to accept new addresses.
    - Add flag to serverdescs to tell whether IPv6 is supported.
  - patch tsocks with our current patches + gethostbyname, getpeername, etc.
  - make freecap (or whichever) do what we want.
  - scrubbing proxies for protocols other than http.
  - We need better default privoxy configs to ship.
  - We need a good scrubbing HTTP proxy; privoxy is unmaintained and sucky.
  - A DNS proxy would let unmodified socks4/socks5 apps to work well.
  - Add SOCKS support to more applications
  - store hidden service information to disk: dirservers forget service
    descriptors when they restart; nodes offering hidden services forget
    their chosen intro points when they restart.