tor/doc/spec/proposals/126-geoip-reporting.txt

Filename: 126-geoip-fetching.txt
Title: Getting GeoIP data and publishing usage summaries
Version: $Revision: 11988 $
Last-Modified: $Date: 2007-10-16 12:59:42 -0400 (Tue, 16 Oct 2007) $
Author: Roger Dingledine
Created: 2007-11-24
Status: Researching

1. Background and motivation

  Right now we can keep a rough count of Tor users, both total and by
  country, by watching connections to a single directory mirror. Being
  able to get usage estimates is useful both for our funders (to
  demonstrate progress) and for our own development (so we know how
  quickly we're scaling and can design accordingly, and so we know which
  countries and communities to focus on more). This need for information
  is the only reason we haven't deployed "directory guards" (think of
  them like entry guards but for directory information; in practice,
  it would seem that Tor clients should simply use their entry guards
  as their directory guards; see also proposal 125).

  With the move toward bridges, we will no longer be able to track Tor
  clients that use bridges, since they use their bridges as directory
  guards. Further, we need to be able to learn which bridges stop seeing
  use from certain countries (and are thus likely blocked), so we can
  avoid giving them out to other users in those countries.

  Right now we already do GeoIP lookups in Vidalia: Vidalia draws relays
  and circuits on its 'network map', and it performs anonymized GeoIP
  lookups to its central servers to know where to put the dots. Vidalia
  caches answers it gets -- to reduce delay, to reduce overhead on
  the network, and to reduce anonymity issues where users reveal their
  knowledge about the network through which IP addresses they ask about.

  But with the advent of bridges, Tor clients are asking about IP
  addresses that aren't in the main directory. In particular, bridge
  users inform the central Vidalia servers about each bridge as they
  discover it and their Vidalia tries to map it.

  Also, we wouldn't mind letting Vidalia do a GeoIP lookup on the client's
  own IP address, so it can provide a more useful map.

  Finally, Vidalia's central servers leave users open to partitioning
  attacks, even if they can't target specific users. Further, as we
  start using GeoIP results for more operational or security-relevant
  goals, such as avoiding or including particular countries in circuits,
  it becomes more important that users can't be singled out in terms of
  their IP-to-country mapping beliefs.

2. The available GeoIP databases

  There are at least two classes of GeoIP database out there: "IP to
  country", which tells us the country code for the IP address but
  no more details, and "IP to city", which tells us the country code,
  the name of the city, and some basic latitude/longitude guesses.

  A recent ip-to-country.csv is 3421362 bytes. Compressed, it is 564252
  bytes. A typical line is:
    "205500992","208605279","US","USA","UNITED STATES"
  http://ip-to-country.webhosting.info/node/view/5

  Similarly, the maxmind GeoLite Country database is also about 500KB
  compressed.
  http://www.maxmind.com/app/geolitecountry

  The maxmind GeoLite City database gives more finegrained detail like
  as geo coordinates and city name. Vidalia currently makes use of this
  information. On the other hand it's 16MB compressed. A typical line is:
    206.124.149.146,Bellevue,WA,US,47.6051,-122.1134
  http://www.maxmind.com/app/geolitecity

  There are other databases out there, like
  http://www.hostip.info/faq.html
  http://www.webconfs.com/ip-to-city.php
  that want more attention, but for now let's assume that all the db's
  are around this size.

3. What we'd like to solve

  Goal #1a: Tor relays collect IP-to-country user stats and publish
  sanitized versions.
  Goal #1b: Tor bridges collect IP-to-country user stats and publish
  sanitized versions.

  Goal #2a: Vidalia learns IP-to-city stats for Tor relays, for better
  mapping.
  Goal #2b: Vidalia learns IP-to-country stats for Tor relays, so the user
  can pick countries for her paths.

  Goal #3: Vidalia doesn't do external lookups on bridge relay addresses.

  Goal #4: Vidalia resolves the Tor client's IP-to-country or IP-to-city
  for better mapping.

  Goal #5: Reduce partitioning opportunities where Vidalia central
  servers can give different (distinguishing) responses.

4. Solution overview

  Our goal is to allow Tor relays, bridges, and clients to learn enough
  GeoIP information so they can do local private queries.

4.1. The IP-to-country db

  Directory authorities should publish a "geoip" file that contains
  IP-to-country mappings. Directory caches will mirror it, and Tor clients
  and relays (including bridge relays) will fetch it. Thus we can solve
  goals 1a and 1b (publish sanitized usage info). Controllers could also
  use this to solve goal 2b (choosing path by country attributes). It
  also solves goal 4 (learning the Tor client's country), though for
  huge countries like the US we'd still need to decide where the "middle"
  should be when we're mapping that address.

  The IP-to-country details are described further in Sections 5 and
  6 below.

4.2. The IP-to-city db

  In an ideal world, the IP-to-city db would be small enough that we
  could distribute it in the above manner too. But for now, it is too
  large. Here's where the design choice forks.

  Option A: Vidalia should continue doing its anonymized IP-to-city
  queries. Thus we can achieve goals 2a and 2b. We would solve goal
  3 by only doing lookups on descriptors that are purpose "general"
  (or, alternately, by only doing lookups on descriptors that are in
  the networkstatus consensus). We would leave goal 5 unsolved.

  Option B: Each directory authority should keep an IP-to-city db,
  lookup the value for each router it lists, and include that line in
  the router's network-status entry. The network-status consensus would
  then use the line that appears in the majority of votes. This approach
  also solves goals 2a and 2b, goal 3 (Vidalia doesn't do any lookups
  at all now), and goal 5 (reduced partitioning risks).

  Option B has the advantage that Vidalia can simplify its operation,
  and the advantage that this consensus IP-to-city data is available to
  other controllers besides just Vidalia. But it has the disadvantage
  that the networkstatus consensus becomes larger, even though most of
  the GeoIP information won't change from one consensus to the next. Is
  there another reasonable location for it that can provide similar
  consensus security properties?

4.3. Recommendation

  My overall recommendation is that we should implement 4.1 soon
  (e.g. early in 0.2.1.x), and we can go with 4.2 option A for now,
  with the hope that later we discover a better way to distribute the
  IP-to-city info and can switch to 4.2 option B.

  Below we discuss more how to go about achieving 4.1.

5. Publishing and caching the GeoIP (IP-to-country) database

  Each v3 directory authority should put a copy of the "geoip" file in
  its datadirectory. Then its network-status votes should include a hash
  of this file (Recommended-geoip-hash: %s), and the resulting consensus
  directory should specify the consensus hash.

  There should be a new URL for fetching this geoip db (by "current.z"
  for testing purposes, and by hash.z for typical downloads). Authorities
  should fetch and serve the one listed in the consensus, even when they
  vote for their own. This would argue for storing the cached version
  in a better filename than "geoip".

  Directory mirrors should keep a copy of this file available via the
  same URLs.

  We assume that the file would change at most a few times a month. Should
  Tor ship with a bootstrap geoip file? An out-of-date geoip file may
  open you up to partitioning attacks, but for the most part it won't
  be that different.

  There should be a config option to disable updating the geoip file,
  in case users want to use their own file (e.g. they have a proprietary
  GeoIP file they prefer to use). In that case we leave it up to the
  user to update his geoip file out-of-band.

  [XXX Should consider forward/backward compatibility, e.g. if we want
  to move to a new geoip file format. -RD]

6. Controllers use the IP-to-country db for mapping and for path building

  Vidalia can use the IP-to-country mappings for placing on its map:
  - The location of the client
  - The location of the bridges, or other relays not in the
    networkstatus, on the map.
  - Any relays that it doesn't yet have an IP-to-city answer for.

  Controllers can also it to set EntryNodes, ExitNodes, etc in a
  per-country way. To support this feature, we need to export the
  IP-to-country data via the Tor controller protocol.

  Is it sufficient just to add a new GETINFO command:
    GETINFO ip-to-country/128.31.0.34
    250+ip-to-country/128.31.0.34="US","USA","UNITED STATES"

7. Relays and bridges use the IP-to-country db for usage summaries

  Once bridges have a GeoIP database locally, they can start to publish
  sanitized summaries of client usage -- how many users they see and from
  what countries. This might also be a more useful way for ordinary Tor
  relays to convey the level of usage they see, which would allow us to
  switch to using directory guards for all users by default.

  But how to safely summarize this information without opening too many
  anonymity leaks seems hard...