mirror of
https://gitlab.torproject.org/tpo/core/tor.git
synced 2024-11-10 13:13:44 +01:00
56 lines
2.8 KiB
Plaintext
56 lines
2.8 KiB
Plaintext
|
|
Part one: Overview and explanation
|
|
|
|
Because tor is an application-level proxy, it needs client-side support
|
|
from every client program that wants to use it. (This is different from
|
|
systems like Freedom, which used a single client-side program to capture
|
|
all packets and redirect them to the Freedom network.) Client applications
|
|
need two general classes of modifications to be compatible with tor:
|
|
|
|
1) Whenever they call connect(), they instead should connect() to the
|
|
local onion proxy and tell it "address and port". The onion proxy will
|
|
itself make a connection to "address and port", and then the client
|
|
application can talk through that socket as if it's directly connected. To
|
|
support as many applications as possible, tor uses the common "socks"
|
|
protocol which does exactly the above. So applications with socks support
|
|
will support tor without needing any modifications.
|
|
|
|
2) Applications must not call gethostbyname() to resolve an address
|
|
they intend to later connect() to via onion routing. gethostbyname()
|
|
contacts the dns server of the target machine -- thus giving away the
|
|
fact that you intend to make an anonymous connection to it.
|
|
|
|
To clarify, I need to explain more about the socks protocol. Socks
|
|
comes in three flavors: 4, 4a, and 5. The socks4 protocol basically
|
|
uses IP and port -- so it is unsuitable because of the gethostbyname()
|
|
issue above. Socks4a is a slight modification to the socks4 protocol,
|
|
whereby you can specify an IP of 0.0.0.x to signal the socks server
|
|
that you will instead be sending a hostname (fqdn). So applications with
|
|
socks4a support are all set. Socks5, on the other hand, allows the client
|
|
to specify "address type" and then an address -- so some applications
|
|
choose to supply an IP and others choose to supply a hostname. If the
|
|
application uses socks5 you must investigate further to decide whether
|
|
it's leaking anonymity.
|
|
|
|
|
|
Part two: using tsocks to transparently replace library calls
|
|
|
|
tsocks (available from http://tsocks.sourceforge.net/ or from your
|
|
favorite apt-get equivalent) allows you to run a program as normal,
|
|
but it replaces the system calls for connect() to connect to the socks
|
|
server first and then pass it your destination info. In our case the
|
|
socks server is a tor process (running either locally or elsewhere).
|
|
In general this works quite well for command-line processes like finger,
|
|
ssh, etc. But there are a couple of catches: A) tsocks doesn't intercept
|
|
calls to gethostbyname. So unless you specify an IP rather than hostname,
|
|
you'll be giving yourself away. B) Programs which are suid root (or
|
|
anybody else) don't let you intercept the system calls -- ssh falls into
|
|
this category. But you can make a local copy of ssh and use that. C)
|
|
Probably tsocks doesn't behave well for behemoths like Mozilla.
|
|
|
|
|
|
Part three: applications which support tor correctly
|
|
|
|
|
|
|