Bitcoin and Tor Support
It is possible to run Bitcoin as a Tor hidden service, and connect to such services.
The following directions assume 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 Tor Project FAQ: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 anonymized, 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
-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.
-onion=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 -noonion
to explicitly disable access to hidden service.
-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
-connect=X When behind 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:
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):
HiddenServicePort 8333 127.0.0.1:8333
HiddenServicePort 18333 127.0.0.1:18333
The directory can be different of course, but (both) port numbers should be equal to your bitcoind’s P2P listen port (8333 by default).
-externalip=X You can tell bitcoin about its publicly 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 -onion=127.0.0.1:9050 -externalip=57qr3yd1nyntf5k.onion -discover