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

Agenda to be resolved:
  remove truncate, truncated from spec?
  remove exit-from-middle from spec?
  add a bit of long-range dummy traffic -- talk to matt
  instrument 'connected' cell.
  find some way to report whether bandwidth limit is being hit.
  begin reputation architecture: kill -USR2 prints opinions about nodes.
  put IPs in directory, not hostnames. keeps OPs from stalling on resolves.
  key rotation:
    tls key rotation
      symmetric and asymmetric
    onion key rotation
    others?
  Advanced directory servers
    Figure out how to do threshold directory servers
    "secondary" directory servers?
      what does it mean for a directory to be valid? do they expire?
  productization:
    preferential per-connection bandwidth limiting
    pre- or post- tls alternate auth mechanisms.
    what we could get from windows developers.
  Look at having smallcells and largecells
  Bandwidth classes. How do we do this so it works?
  Rendezvous point design and spec.
  Non-clique topologies -- easy to implement, hard to decide topology.
  Certification/accreditation
  Extensible spec:
    - e.g. 'router' line more flexible in descriptor
    - split spec file into mini spec files? finalize some, leave others open?
  Usability
    - e.g. if no torrc, use acceptable defaults.
  Synchronous design?
  Helper nodes?
  Interoperability with morphmix
  plan the codecon talk.

Bugs:
        - Sometimes it picks a middleman node as the exit for a circuit.
        - if you specify a non-dirserver as exitnode or entrynode, when it
          makes the first few circuits it hasn't yet fetched the directory,
          so it warns that it doesn't know the node.
        - make 'make test' exit(1) if a test fails.
        - fix buffer unit test so it passes

Short-term:
        - when you hup, rewrite the router.desc file (and maybe others)
        - consider handling broken socks4 implementations
        - improve how it behaves when i remove a line from the approved-routers files
        - Make tls connections tls_close intentionally
        o Rename ACI to circID
        . integrate rep_ok functions, see what breaks
        - update tor faq
        o obey SocksBindAddress, ORBindAddress
        o warn if we're running as root
        o make connection_flush_buf() more obviously obsolete
        o let hup reread the config file, eg so we can get new exit
          policies without restarting
        o Put recommended_versions in a config entry
        X use times(2) rather than gettimeofday to measure how long it
          takes to process a cell
        o Separate trying to rebuild a circuit because you have none from trying 
          to rebuild a circuit because the current one is stale
        X Continue reading from socks port even while waiting for connect.
        o Exit policies
                o Spec how to write the exit policies
                o Path selection algorithms
                        o Choose path more incrementally
                        o Let user request first/last node
                        o And disallow certain nodes
                        D Choose path by jurisdiction, etc?
                o Make relay end cells have failure status and payload attached
        X let non-approved routers handshake.
        - Dirserver shouldn't put you in running-routers list if you haven't
          uploaded a descriptor recently
        . migrate to using nickname rather than addr:port for routers
                o decide_aci_type
                - generate onion skins
                  - circuit_send_next_onion_skin
                  - circuit_extend
                  - onion_generate_cpath
                - get_unique_aci_by_addr_port
                - circ->n_addr and circ->n_port
                  - circuit_enumerate_by_naddr_nport
                - cpath layers
                - connection_or_connect
                - connection_exact_get_by_addr_port
                - connection_twin_get_by_addr_port
                - router_get_by_addr_port
                - connection_or_init_conn_from_router
                - tag_pack, tag_unpack, connection_cpu_process_inbuf
                - directory_initiate_command
        . Move from onions to ephemeral DH
                o incremental path building
                o transition circuit-level sendmes to hop-level sendmes
                o implement truncate, truncated
                o move from 192byte DH to 128byte DH, so it isn't so damn slow
                - exiting from not-last hop
                        - OP logic to decide to extend/truncate a path
                        - make sure exiting from the not-last hop works
                        - logic to find last *open* hop, not last hop, in cpath
        o Remember address and port when beginning. 
        - Extend by nickname/hostname/something, not by IP.
        - Need a relay teardown cell, separate from one-way ends.
        - remove per-connection rate limiting
        - Make it harder to circumvent bandwidth caps: look at number of bytes
          sent across sockets, not number sent inside TLS stream.

On-going
        . Better comments for functions!
        . Go through log messages, reduce confusing error messages.
        . make the logs include more info (fd, etc)
        . Unit tests
        . Update the spec so it matches the code

Mid-term:
        - Rotate tls-level connections -- make new ones, expire old ones.
          So we get actual key rotation, not just symmetric key rotation
        o Are there anonymity issues with sequential streamIDs? Sequential
          circIDs? Eg an attacker can learn how many there have been.
          The fix is to initialize them randomly rather than at 1.
        - Look at having smallcells and largecells
        . Redo scheduler
                o fix SSL_read bug for buffered records
                - make round-robining more fair
        - What happens when a circuit's length is 1? What breaks?
        . streams / circuits
                o Implement streams
                o Rotate circuits after N minutes?
                X Circuits should expire when circuit->expire triggers
NICK            . Handle half-open connections
                        o openssh is an application that uses half-open connections
                        o Figure out what causes connections to close, standardize
                          when we mark a connection vs when we tear it down
                o Look at what ssl does to keep from mutating data streams
        o Put CPU workers in separate processes
                o Handle multiple cpu workers (one for each cpu, plus one)
                o Queue for pending tasks if all workers full
                o Support the 'process this onion' task
                D Merge dnsworkers and cpuworkers to some extent
                o Handle cpuworkers dying
        . Scrubbing proxies
                - Find an smtp proxy?
                        - Check the old smtp proxy code
                o Find an ftp proxy? wget --passive
                D Wait until there are packet redirectors for Linux
                . Get socks4a support into Mozilla
        . Develop rendezvous points
                X Handle socks commands other than connect, eg, bind?
                o Design
                - Spec
                - Implement
        . Tests
                o Testing harness/infrastructure
                D System tests (how?)
                - Performance tests, so we know when we've improved
                        . webload infrastructure (Bruce)
                        . httperf infrastructure (easy to set up)
                        . oprofile (installed in RH >8.0)
NICK    . Daemonize and package
                o Teach it to fork and background
                - Red Hat spec file
                o Debian spec file equivalent
        . Portability
                . Which .h files are we actually using?
                . Port to:
                        o Linux
                        o BSD
                        . Solaris
                        o Cygwin
                        . Win32
                        o OS X
                - deal with pollhup / reached_eof on all platforms
                o openssl randomness
                o inet_ntoa
                o stdint.h
                - Make a script to set up a local network on your machine
        o More flexibility in node addressing
                D Support IPv6 rather than just 4
                o Handle multihomed servers (config variable to set IP)

In the distant future:
        D Load balancing between router twins
                D Keep track of load over links/nodes, to
                  know who's hosed
SPEC!!  D Non-clique topologies
        D Implement our own memory management, at least for common structs
          (Not ever necessary?)
        D Advanced directory servers
                D Automated reputation management
SPEC!!          D Figure out how to do threshold directory servers
                D jurisdiction info in dirserver entries? other info?

Older (done) todo stuff:

For 0.0.2pre17:
        o Put a H(K | handshake) into the onionskin response
        o Make cells 512 bytes
        o Reduce streamid footprint from 7 bytes to 2 bytes
          X Check for collisions in streamid (now possible with
            just 2 bytes), and back up & replace with padding if so
        o Use the 4 reserved bytes in each cell header to keep 1/5
          of a sha1 of the ongoing relay payload (move into stream header)
        o Move length into the stream header too
        o Make length 2 bytes
        D increase DH key length
        D increase RSA key length
        D Spec the stream_id stuff. Clarify that nobody on the backward
          stream should look at stream_id.

Cell:
        ACI (anonymous circuit identifier)    [2 bytes]
        Command                               [1 byte]
        Payload (padded with 0 bytes)         [509 bytes]

Relay payload:
        Relay command           [1 byte]
        Stream ID               [7 bytes]
        Partial SHA-1           [4 bytes]
        Length                  [2 bytes]
        Relay payload           [495 bytes]

For 0.0.2pre15:
        o don't pick exit nodes which will certainly reject all things.
        o don't pick nodes that the directory says are down
        o choose randomly from running dirservers, not just first one
        o install the man page
        o warn when client-side tries an address/port which no router in the dir accepts.

For 0.0.2pre14:
        o More flexible exit policies (18.*, 18.0.0.0/8)
        o Work to succeed in the precense of exit policy violation
                o Replace desired_path_len with opaque path-selection specifier
                o Client-side DNS caching
                o Add entries to client DNS cache based on END cells
                o Remove port from END_REASON_EXITPOLICY cells
                o Start building new circuits when we get an exit-policy
                  failure.  (Defer exiting from the middle of existing
                  circuits or extending existing circuits for later.)
                o Implement function to check whether a routerinfo_t 
                  supports a given exit addr.
                o Choose the exit node of an in-progress circuit based on
                  pending AP connections.
                o Choose the exit node _first_, then beginning, then
                  middle nodes.

Previous:
        o Get tor to act like a socks server
                o socks4, socks4a
                o socks5
        o routers have identity key, link key, onion key.
                o link key certs are
                  D signed by identity key
                  D not in descriptor
                  o not in config
                  D not on disk
                o identity and onion keys are in descriptor (and disk)
        o upon boot, if it doesn't find identity key, generate it and write it.
        o also write a file with the identity key fingerprint in it
        o router generates descriptor: flesh out router_get_my_descriptor()
        o Routers sign descriptors with identity key
        o routers put version number in descriptor
        o routers should maybe have `uname -a` in descriptor?
        o Give nicknames to routers
                o in config
                o in descriptors
        o router posts descriptor
                o when it boots
                o every DirFetchPostPeriod seconds
                D when it changes
        o change tls stuff so certs don't get written to disk, or read from disk
        o make directory.c 'thread'safe
        o dirserver parses descriptor
        o dirserver checks signature
        D client checks signature?
        o dirserver writes directory to file
          o reads that file upon boot
        o directory includes all routers, up and down
        o add "up" line to directory, listing nicknames
        o instruments ORs to report stats
          o average cell fullness
          o average bandwidth used
        o configure log files. separate log file, separate severities.
        o what assumptions break if we fclose(0) when we daemonize?
        o make buffer struct elements opaque outside buffers.c
        o add log convention to the HACKING file
        o make 'make install' do the right thing
        o change binary name to tor
        o change config files so you look at commandline, else look in
          /etc/torrc. no cascading.
        o have an absolute datadir with fixed names for files, and fixed-name
          keydir under that with fixed names
        o Move (most of) the router/directory code out of main.c
        o Simple directory servers
                o Include key in source; sign directories
                        o Signed directory backend
                        o Document
                        o Integrate
                o Add versions to code
                o Have directories list recommended-versions
                        o Include line in directories
                        o Check for presence of line.
                        o Quit if running the wrong version
                        o Command-line option to override quit
                o Add more information to directory server entries
                        o Exit policies
        o Clearer bandwidth management 
                o Do we want to remove bandwidth from OR handshakes?
                o What about OP handshakes?
        X Move away from openssl
                o Abstract out crypto calls
                X Look at nss, others? Just include code?
        o Use a stronger cipher
                o aes now, by including the code ourselves
        X On the fly compression of each stream
        o Clean up the event loop (optimize and sanitize)
        o Remove that awful concept of 'roles'
        o Terminology
                o Circuits, topics, cells stay named that
                o 'Connection' gets divided, or renamed, or something?
        o DNS farm
                o Distribute queries onto the farm, get answers
                o Preemptively grow a new worker before he's needed
                o Prune workers when too many are idle
                o DNS cache   
                        o Clear DNS cache over time  
                        D Honor DNS TTL info (how??)
                o Have strategy when all workers are busy
                o Keep track of which connections are in dns_wait
                o Need to cache positives/negatives on the tor side
                        o Keep track of which queries have been asked
                o Better error handling when
                        o An address doesn't resolve
                        o We have max workers running
                o Consider taking the master out of the loop?
        X Implement reply onions
        o Total rate limiting
        o Look at OR handshake in more detail
                o Spec it
                o Merge OR and OP handshakes
                o rearrange connection_or so it doesn't suck so much to read
                D Periodic link key rotation. Spec?
        o wrap malloc with something that explodes when it fails
        o Clean up the number of places that get to look at prkey