TOR SUPPORT IN BITCOIN
======================

It is possible to run Bitcoin as a Tor hidden service, and connect to such services.

The following assumes you have a Tor proxy running on port 9050. Many distributions
default to having a SOCKS proxy listening on port 9050, but others may not.
In particular, the Tor Browser Bundle defaults to listening on a random port. See
https://www.torproject.org/docs/faq.html.en#TBBSocksPort for how to properly
configure Tor.


1. Run bitcoin behind a Tor proxy
---------------------------------

The first step is running Bitcoin behind a Tor proxy. This will already make all
outgoing connections be anonimized, but more is possible.

-socks=5        SOCKS5 supports connecting-to-hostname, which can be used instead
                of doing a (leaking) local DNS lookup. SOCKS5 is the default,
                but SOCKS4 does not support this. (SOCKS4a does, but isn't
                implemented).

-proxy=ip:port  Set the proxy server. If SOCKS5 is selected (default), this proxy
                server will be used to try to reach .onion addresses as well.

-tor=ip:port    Set the proxy server to use for tor hidden services. You do not
                need to set this if it's the same as -proxy. You can use -notor
                to explicitly disable access to hidden service.

-dnsseed        DNS seeds are not resolved directly when a SOCKS5 proxy server is
                set. Rather, a short-lived proxy connection to the dns seed
                hostname is attempted, and peer addresses are requested.

-listen         When using -proxy, listening is disabled by default. If you want
                to run a hidden service (see next section), you'll need to enable
                it explicitly.

-connect=X      When behing a Tor proxy, you can specify .onion addresses instead
-addnode=X      of IP addresses or hostnames in these parameters. It requires
-seednode=X     SOCKS5. In Tor mode, such addresses can also be exchanged with
                other P2P nodes.

In a typical situation, this suffices to run behind a Tor proxy:

  ./bitcoin -proxy=127.0.0.1:9050


2. Run a bitcoin hidden server
------------------------------

If you configure your Tor system accordingly, it is possible to make your node also
reachable from the Tor network. Add these lines to your /etc/tor/torrc (or equivalent
config file):

  HiddenServiceDir /var/lib/tor/bitcoin-service/
  HiddenServicePort 8333 127.0.0.1:8333

The directory can be different of course, but (both) 8333's should be equal to your
bitcoind's P2P listen port (8333 by default).

-externalip=X   You can tell bitcoin about its publically reachable address using
                this option, and this can be a .onion address. Given the above
                configuration, you can find your onion address in
                /var/lib/tor/bitcoin-service/hostname. Onion addresses are given
                preference for your node to advertize itself with, for connections
                coming from unroutable addresses (such as 127.0.0.1, where the
                Tor proxy typically runs).

-listen         You'll need to enable listening for incoming connections, as this
                is off by default behind a proxy.

-discover       When -externalip is specified, no attempt is made to discover local
                IPv4 or IPv6 addresses. If you want to run a dual stack, reachable
                from both Tor and IPv4 (or IPv6), you'll need to either pass your
                other addresses using -externalip, or explicitly enable -discover.
                Note that both addresses of a dual-stack system may be easily
                linkable using traffic analysis.

In a typical situation, where you're only reachable via Tor, this should suffice:

  ./bitcoind -proxy=127.0.0.1:9050 -externalip=57qr3yd1nyntf5k.onion -listen

(obviously replace the Onion address with your own). If you don't care too much
about hiding your node, and want to be reachable on IPv4 as well, additionally
specify:

  ./bitcoind ... -discover

and open port 8333 on your firewall (or use -upnp).

If you only want to use Tor to reach onion addresses, but not use it as a proxy
for normal IPv4/IPv6 communication, use:

  ./bitcoin -tor=127.0.0.1:9050 -externalip=57qr3yd1nyntf5k.onion -discover