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:
N - Mark up spec; note unclear points about servers
N - Clean up dir spec.
N . contact umass folks
N - Mention controller libs someplace.
  D 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.
R . 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 windows 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'
  - 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 0.1.1.10-alpha:
N - if they're trying to be a tor server and they're running
    win 98 or win me, don't let them be a server.
  o ReachableAddresses doesn't do what we want wrt dir fetches.

for 0.1.1.x:
N . Additional controller features
      o Find a way to make event info more extensible
      - 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.
R       - What do we want here, exactly?
N       - Specify and implement it.
      - Change stream status events analogously.
R       - What do we want here, exactly?
N       - Specify and implement it.
      - Make other events "better".
      - Change stream status events analogously.
R       - What do we want here, exactly?
N       - Specify and implement it.
      - Make other events "better" analogously
R       - What do we want here, exactly?
N       - 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.

  . Helper nodes
    . More testing and debugging
    o On sighup, if usehelpernodes changed to 1, use new circuits?
    - If your helper nodes are unavailable, don't abandon them unless
      other nodes *are* reachable.
    o If you think an OR conn is open but you can never establish a circuit
      to it, reconsider whether it's actually open.

  - 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.

  - 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

  - Bind to random port when making outgoing connections to Tor servers,
    to reduce remote sniping attacks.
  - When we connect to a Tor server, it sends back a signed cell listing
    the IP it believes it is using. Use this to block dvorak's attack.

N - Destroy and truncated cells should have reasons.
N - 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.)

N - warn if listening for SOCKS on public IP.

  - cpu fixes:
    - see if we should make use of truncate to retry
    o hardware accelerator support (configure engines.)
    o hardware accelerator support (use instead of aes.c when reasonable)
      - Benchmark this somehow to see whether using EVP_foo is slower in the
        non-engine case than AES_foo.  If so, check for AES engine and fall
        back to AES_foo when it's not found.
R   - kill dns workers more slowly

  . Directory changes
    o recommended-versions for client / server ?
    . Some back-out mechanism for auto-approval
      o dirservers have blacklist of IPs and keys 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

R   . Dirservers verify reachability claims
      o basic reachability testing, influencing network-status list.
      X rate-limiting the reporting of trouble servers
R     - check reachability as soon as you hear about a new server

    - Decentralization
      - Figure out what to do about hidden service descriptors.
      - find 10 dirservers.
        - (what are criteria to be a dirserver?)
      o Dirservers publish compressed network-status objects.
        o Support retrieving several-at-once
      o Everyone downloads network-status objects
        o Clients: from all directories, round-robin
          o Basic implementation: disable until 0.1.1.x is out.
          o On failure, mark trusted_dir_server as having failed
          o Retry, up to a point.
          - Launch retry immediately on failure.
        o Parse them
        o Cache them, reload on restart
        o Serve cached directories
      o Directories expose individual descriptors
        X By 'if-newer-than' (Does the spec require this??)
        o Support compression.
      o Alice acts on network-status objects
        o Alice downloads descriptors as needed.
          o Figure out what's needed
          o Store it
            o Implement store
            o Implement reload-from-store
            o Store downloaded descriptors
          o Download it
            o As-needed if we have 2 network-status objs.
            o Download "all" if we have less than 2 network-status objs.
              (This has vulnerabilities if we're not careful)
            o Call directory_has_arrived as needed; rename it.
            o Set has_fetched_directory properly.
          o Retry descriptors on failure
          o Give up after a while.
          - But try again after a long while (???)
        o Check software versions according to some sane plan.
          - Warn again after 24 hours.
        o Alice sets descriptor status from network-status
          o Implement
          o Use
N     . Routerdesc download changes
        o Refactor combined-status to be its own type.
        o Change rule from "do not launch new connections when one exists" to
          "do not request any fingerprint that we're currently requesting."
        o Launch connections every minute, or whenever a download fails
        o Retry failed routerdescs after 0, 1, 5, 10 minutes.
          o Mirrors retry harder and more often. (0, 0, 1, 1, 2, 5, and 15)
        o Reset failure count every 60 minutes
        o Drop fallback to download-all.  Also, always split download.
        - Only use a routerdesc if you recognize its hash.
          - (Must defer till dirservers are upgraded to latest code, which
            actually generates these hashes.)
          - Of course, authdirservers must not do this.
          - Should directory mirrors do something else entirely?
        - Use has_fetched_directory sanely, whatever that means.
          - What *does* that mean?
        o If we have a routerdesc for Bob, and he says, "I'm 0.1.0.x", don't
          fetch a new one if it was published in the last 2 hours.
          - How does this interact with the 'recognized hash' rule?
      . Downgrade new directory events from notice to info
      - Clients should estimate their skew as median of skew from directory
        connections over last N seconds.
      o Call dirport_is_reachable from somewhere else.
      o Networkstatus should list who's an authority.
      o Add nickname element to dirserver line.  Log this along with IP:Port.
      o Warn when using non-default directory servers.
      o When giving up on a non-finished dir request, log how many bytes
        dropped, to see whether it's worthwhile to use partial info.
    - Security
      - Alices avoid duplicate class C nodes.
      - Analyze how bad the partitioning is or isn't.
    - Flags
      - Clients use Stable and Fast instead of uptime and bandwidth to
        pick which servers are stable/fast.

    - Make authorities rate-limit logging their complaints about given
      servers?

  - packaging and ui stuff:
    . multiple sample torrc files
    - uninstallers
      . for os x
    . figure out how to make nt service stuff work?
      . Document it.
    . Add version number to directory.
N   - Vet all pending installer patches
      - Win32 installer plus privoxy, sockscap/freecap, etc.
      - Vet win32 systray helper code

  - document:
    - torcp needs more attention in the tor-doc-win32.
    - recommend gaim.
    - unrecommend IE because of ftp:// bug.
    - torrc.complete.in needs attention?

Reach (deferrable) items for 0.1.1.x:
  - Start using create-fast cells as clients
  o Let more config options (e.g. ORPort) change dynamically.
  - start handling server descriptors without a socksport?
  o Add TTLs to DNS-related replies, and use them (when present) to adjust
    addressmap values.

  . Update the hidden service stuff for the new dir approach.
    - switch to an ascii format.
    - 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.

  . 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.

  . Research 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?)

  - Make router_is_general_exit() a bit smarter once we're sure what it's for.

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.
  o 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 (we switch to a new one after a week, but
    old circuits don't get any benefit from this).
  - 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)