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

Flag-day changes: (things which are backward incompatible)
        . remove link key from directories, from connection_t.
          (just get it from the tls cert)
        . make onion keys include oaep padding, so you can tell
          if you decrypted it correctly
        . add bandwidthrate and bandwidthburst to server descriptor
        - directories need to say who signed them.
        - what other pieces of the descriptors need to change?
          maybe add a section for who's connected to a given router?
          add a flexible section for reputation info?


Bugs:
        o we call signal(), but we should be calling sigaction()
        o send socks rejects when things go bad ?
        o on solaris, need to build with
          LDFLAGS="-lsocket -lnsl" ./configure
        o on solaris, we HAVE_UNAME but the uname() call fails?
        . should maybe make clients exit(1) when bad things happen?
          e.g. clock skew.
        o client-side dns cache doesn't appear to be getting populated
          by 'connected' cells. In fact, the 'connected' cells don't even
          include the IP.
        o When it can't resolve any dirservers, it is useless from then on.
          We should make it reload the RouterFile if it has no dirservers.
        o Sometimes it picks a middleman node as the exit for a circuit.
        o 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.
        o make 'make test' exit(1) if a test fails.
        . fix buffer unit test so it passes

Short-term:
        - should retry exitpolicy end streams even if the end cell didn't
          resolve the address for you
        o add in 'notice' log level
        X make recommendedversions different for clients and servers.
          e.g. C0.0.3 vs S0.0.3?
        o put IP into the descriptor, so clients don't need to resolve things
        o when you hup, rewrite the router.desc file (and maybe others)
        - consider handling broken socks4 implementations
        o improve how it behaves when i remove a line from the approved-routers files
        - Make tls connections tls_close intentionally
        - Add '[...truncated]' or similar to truncated log entries (like the directory
          in connection_dir_process_inbuf()).
        . Make logs handle it better when writing to them fails.
        o leave server descriptor out of directory if it's too old
        o Rename ACI to circID
        o 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.
        X Dirserver shouldn't put you in running-routers list if you haven't
          uploaded a descriptor recently
        X migrate to using nickname rather than addr:port for routers
        - migrate to using IPv6 sizes everywhere
        o 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
                X exiting from not-last hop
                        X OP logic to decide to extend/truncate a path
                        X make sure exiting from the not-last hop works
                        X 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.
        X 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.
        o Audit users of connnection_remove and connection_free outside of
          main.c; many should use mark_for_close instead.

Rendezvous service:
        o Design and specify protocol
        o Possible preliminary refactoring:
            o Should we break circuits up into "circuit-with-cpath" and
              "circuit-without-cpath"?
            o We need a way to tag circuits as special-purpose circuits for:
                o Connecting from Bob's OP to the introduction point
                o Sending introduction requests from the IPoint to Bob
                o Connecting from Alice to the rendezvous point for Bob
                o Connecting from Bob to the rendezvous point for Alice
                o Waiting at a rendezvous point to be joined
                o Joined to another circuit at the rendezvous point.
              (We should also enumerate all the states that these operations
              can be in.) [NM]
            o Add circuit metadata [NM]
        o Code to configure hidden services [NM] 4 hours
        o Service descriptors
            o OPs need to maintain identity keys for hidden services [NM]
            o Code to generate and parse service descriptors [NM]
        o Advertisement
            o Generate y.onion hostnames [NM]
                o Store y.onion hostnames to disk. [NM]
            o Code to do an HTTP connection over Tor from within Tor [RD]
            o Publish service descriptors to directory [RD]
            o Directory accepts and remembers service descriptors, and
              delivers them as requested
                o Frontend [RD]
                o Backend [NM]
            o Code for OPs to retrieve (and cache?) service descriptors [RD]
        o Rendezvous
            o Code as needed to generate and parse all rendezvous-related
              cell types, and do all handshaking [NM]
            o ORs implement introduction points
            o OPs with hidden services establish introduction points
            o ORs implement rendezvous points
            o OPs notice y.onion URLs, and:
                o Retrieve service descriptors
                o Establish rendezvous points
                o Send introduction requests to introduction points
        o Communication
            o OPs remember which circuits are used for which rendezvous
              points, and can look up circuits by location-hidden service
            o OPs send/handle BEGIN cells for location-hidden services
            o End-to-end communication for location-hidden services
        o a section in the man pages: how to configure hidden services
        o let bob use himself as a rendezvous point
        o let bob choose himself as intro point
        o let bob replenish his intro points and republish
        o alice retries introduction and rendezvous a few times?
        o ORs should not pick themselves while building general circs
        o should alice ever try to refresh her service desc cache entries?
          should she expire them after e.g. 15 mins?
        o race condition: alice has the serverdesc in her cache, she opens
          the circs, serverdesc expires and is flushed, then she goes
          to send the intro cell. should serverdesc cache have a
          last-touched field? are there better fixes?
        o backward compatibility: when only certain nodes know about rend
          protocol, how do we deal? have nodes parse the tor version field?
          force an upgrade? simply be more robust against useless nodes?
        o should expire rend streams when too much time has passed
        o should make failed rend/intro circs count toward alice's
          num_failed circs, to prevent madness when we're offline (But
          don't count failed rend circs toward Bob's total, or Alice
          can bork him.)
        o deal with edge_type in connection_edge.c
        o retry end for certain reasons (resolvefailed, policyfailed)
        - preemptively build and start rendezvous circs
        - preemptively build n-1 hops of intro circs?
        o (n)ack introduction requests?
        - cannibalize general circs?
        D how to set up multiple locations for a hidden service?
        o make bob publish only established intro circs?
        o when bob tries to connect to alice's chosen rend point, but
          can't, but it's not the fault of the last hop in the rend
          circ, then he should retry?
        - 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.

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:
        o 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.
        - Rotate tls-level connections -- make new ones, expire old ones.
          So we get actual key rotation, not just symmetric key rotation
        - And learn to transfer a circuit from one conn to another, so we
          can empty conns to expire them.
        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
        . 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
                        o 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 tunnel tor cell protocol over http, for people who need to
          do http
        D better transport than tcp: reliable is necessary, but
          out-of-order delivery is fine (to some extent).
        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 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.

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