Commit bec9653f authored by Roger Dingledine's avatar Roger Dingledine
Browse files

clean up the torbl-design draft


svn:r9835
parent a48329d4
......@@ -7,27 +7,28 @@ Status:
Why?
It's useful for third parties to be able to tell when they've got a
connection from a Tor exit node. Potential aplications range from
It's useful for third parties to be able to tell when a given connection
is coming from a Tor exit node. Potential applications range from
"anonymous user" cloaks on IRC networks like oftc, to networks like
Freenode that apply special authentication rules to users from these
IPs, to systems like Wikipedia that want to make a priority of
IPs, to systems like Wikipedia that may want to make a priority of
_unblocking_ shared IPs more liberally than non-shared IPs, since shared
IPs presumably have non-abusive users as well as abusive ones.
Since Tor provides exit policies, not every Tor server will connect to
every address:port combination on the Internet. Unless you're trying to
penalize hosts for supporting anonymity, it makes more sense to answer
the fine-grained question "which Tor servers will connect to _me_" than
the fine-grained question "which Tor servers will connect to _me_?" than
the coarse-grained question "which Tor servers exist?" The fine-grained
approach also helps Tor server ops who share an IP with their Tor
server: if they want to access a site that blocks Tor users, they can
add that site to their exit policy, and the site can learn that they
won't send it anonymous connections.
Tor already ships with a tool (the "exitlist" script) to identify which
Tor nodes might open anonymous connections to any given exit address.
But this is a bit tricky to set up, and isn't seeing much use.
server: if they want to access a site that blocks Tor users, they
can exclude that site from their exit policy, and the site can learn
that they won't send it anonymous connections.
Tor already ships with a tool (the "contrib/exitlist" script) to
identify which Tor nodes might open anonymous connections to any given
exit address. But this is a bit tricky to set up, so only sites like
Freenode and OFTC that are dedicated to privacy use it.
Conversely, providers of some DNSBL implementations are providing
coarse-grained lists of Tor hosts -- sometimes even listing servers that
permit no exit connections at all. This is rather a problem, since
......@@ -40,9 +41,12 @@ How?
cached-routers.new files as new routers arrive. To tell whether a given
server allows connections to a certain address:port combo, look at the
definitions in dir-spec.txt or follow the logic of the current exitlist
script.
script. If bug 405 is still open when you work on this
(http://bugs.noreply.org/flyspray/index.php?do=details&id=405), you'll
probably want to extend it to look at only the newest descriptor for
each server, so you don't use obsolete exit policy data.
FetchUselessDescriptors would probably be a good option to enable.
FetchUselessDescriptors would probably be a good torrc option to enable.
If you're also running a directory cache, you get extra-fresh
information.
......@@ -61,7 +65,7 @@ The DNS interface
possibly a bad idea.
"General IP:Port"
Query type 1: "General IP:Port"
Format:
{IP1}.{port}.{IP2}.ip-port.torhosts.example.com
......@@ -77,7 +81,7 @@ The DNS interface
Example use:
I'm running an IRC server at w.x.y.z:9999, and I want to tell
whether an incoming connections are from Tor servers. I set
whether an incoming connection is from a Tor server. I set
up my IRC server to give a special mask to any user coming from
an IP listed in 9999.z.y.x.w.ip-port.torhosts.example.com.
......@@ -86,7 +90,7 @@ The DNS interface
if it's a Tor server that allows connections to my ircd.
"IP-port group."
Query type 2: "IP-port group"
Format:
{IP}.{listname}.list.torhosts.example.com
......@@ -100,7 +104,7 @@ The DNS interface
Suppose torhosts.example.com has a list of IP:Port called "foo".
There is an A record for 4.3.2.1.foo.list.torhosts.example.com
if and only if 1.2.3.4 is a Tor server that permits connections
to one of the addresses in list "foo|.
to one of the addresses in list "foo".
Example use:
Suppose torhosts.example.com has a list of hosts in "examplenet",
......@@ -116,7 +120,7 @@ The DNS interface
just a few foonet addresses to my exit policy.
"My IP, with port."
Query type 3: "My IP, with port"
Format:
{IP}.{port}.me.torhosts.example.com
......@@ -138,8 +142,7 @@ The DNS interface
This would be easiest to use, but DNS gets in the way. If you
create DNS records that give different results depending on who is
asking, you mess up caching. There could be a fix here, but might
now.
here.
not.
RECOMMENDATION: Just build ip-port for now, and see what demand is
......@@ -157,4 +160,7 @@ Other issues:
masks wider than /8 make me nervous here, as do port ranges.
We need an answer for what to do about hosts which exit from different
IPs than their advertised IP.
IPs than their advertised IP. One approach would be for the DNSBL
to launch periodic requests to itself through all exit servers whose
policies allow it -- and then see where the requests actually come from.
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