Some documentation about tor

doc/Tor.txt

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+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
+