It is possible to run Bitcoin Core as a Tor onion 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 port 9150.
services (Tor v3). Tor v2 addresses are ignored by Bitcoin Core and neither relayed nor stored.
There are several ways to see your local onion address in Bitcoin Core:
-netinfogetnetworkinfo.onion)You may set the -debug=tor config logging option to have additional
information in the debug log about your Tor configuration.
CLI -addrinfo returns the number of addresses known to your node per
network. This can be useful to see how many onion peers your node knows,
e.g. for -onlynet=onion.
You can use the getnodeaddresses RPC to fetch a number of onion peers known to your node; run bitcoin-cli help getnodeaddresses for details.
bitcoin rpc can also be substituted for bitcoin-cli.
The first step is running Bitcoin Core behind a Tor proxy. This will already anonymize all outgoing connections, but more is possible.
-proxy=ip[:port] Set the proxy server. It will be used to try to reach .onion addresses as well. You need to use -noonion or -onion=0 to explicitly disable outbound access to onion services.
-proxy=ip[:port]=tor or -onion=ip[:port] Set the proxy server for reaching .onion addresses. You do not need to set this if it's the same as the generic -proxy. You can use -onion=0 to explicitly disable access to onion services.
Note: The proxy for DNS requests is taken from -proxy=addr:port or -proxy=addr:port=ipv4 or -proxy=addr:port=ipv6 (last one if multiple options are given). It is not taken from -proxy=addr:port=tor or -onion=addr:port. If no proxy for DNS requests is configured, then they will be done using the functions provided by the operating system, most likely resulting in them being done over the clearnet to the DNS servers of the internet service provider.
If -proxy or -onion is specified multiple times, later occurrences override
earlier ones and command line overrides the config file. UNIX domain sockets may
be used for proxy connections. Set -onion or -proxy to the local socket path
with the prefix unix: (e.g. -onion=unix:/home/me/torsocket).
-listen When using -proxy, listening is disabled by default. If you want to manually configure an onion service (see section 3), you'll need to enable it explicitly.
-connect=X -addnode=X -seednode=X When behind a Tor proxy, you can specify .onion addresses instead of IP addresses or hostnames in these parameters. Such addresses can also be exchanged with other P2P nodes.
-onlynet=onion Make automatic outbound connections only to .onion addresses. Inbound and manual connections are not affected by this option. It can be specified multiple times to allow multiple networks, e.g. onlynet=onion, onlynet=i2p, onlynet=cjdns.
In a typical situation, this suffices to run behind a Tor proxy:
bitcoind -proxy=127.0.0.1:9050
bitcoin node or bitcoin gui can also be substituted for bitcoind.
Bitcoin Core makes use of Tor's control socket API to create and destroy ephemeral onion services programmatically. This means that if Tor is running and proper authentication has been configured, Bitcoin Core automatically creates an onion service to listen on. The goal is to increase the number of available onion nodes.
This feature is enabled by default if Bitcoin Core is listening (-listen) and
it requires a Tor connection to work. It can be explicitly disabled with
-listenonion=0. If it is not disabled, it can be configured using the
-torcontrol and -torpassword settings.
To see verbose Tor information in the bitcoind debug log, pass -debug=tor.
You may need to set up the Tor Control Port. On Linux distributions there may be
some or all of the following settings in /etc/tor/torrc, generally commented
out by default (if not, add them):
ControlPort 9051
CookieAuthentication 1
CookieAuthFileGroupReadable 1
DataDirectoryGroupReadable 1
Add or uncomment those, save, and restart Tor (usually systemctl restart tor
or sudo systemctl restart tor on most systemd-based systems, including recent
Debian and Ubuntu, or just restart the computer).
Connecting to Tor's control socket API requires one of two authentication
methods to be configured: cookie authentication or bitcoind's -torpassword
configuration option.
For cookie authentication, the user running bitcoind must have read access to
the CookieAuthFile specified in the Tor configuration. In some cases this is
preconfigured and the creation of an onion service is automatic. Don't forget to
use the -debug=tor bitcoind configuration option to enable Tor debug logging.
If a permissions problem is seen in the debug log, e.g. `tor: Authentication cookie /run/tor/control.authcookie could not be opened (check permissions)`, it can be resolved by adding both the user running Tor and the user running bitcoind to the same Tor group and setting permissions appropriately.
On Debian-derived systems, the Tor group will likely be debian-tor and one way
to verify could be to list the groups and grep for a "tor" group name:
getent group | cut -d: -f1 | grep -i tor
You can also check the group of the cookie file. On most Linux systems, the Tor
auth cookie will usually be /run/tor/control.authcookie:
TORGROUP=$(stat -c '%G' /run/tor/control.authcookie)
Once you have determined the ${TORGROUP} and selected the ${USER} that will
run bitcoind, run this as root:
usermod -a -G ${TORGROUP} ${USER}
Then restart the computer (or log out) and log in as the ${USER} that will run
bitcoind.
torpassword authenticationFor the -torpassword=password option, the password is the clear text form that
was used when generating the hashed password for the HashedControlPassword
option in the Tor configuration file.
The hashed password can be obtained with the command `tor --hash-password password` (refer to the [Tor Dev Manual](https://2019.www.torproject.org/docs/tor-manual.html.en) for more details).
You can also manually configure your node to be 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 127.0.0.1:8334
# If tor --list-modules shows "pow: yes", then enable PoW protection.
# It is available in tor-0.4.8.1-alpha and newer when configured with
# ./configure --enable-gpl.
HiddenServicePoWDefensesEnabled 1
The directory can be different of course, but virtual port numbers should be equal to your bitcoind's P2P listen port (8333 by default), and target addresses and ports should be equal to binding address and port for inbound Tor connections (127.0.0.1:8334 by default).
-externalip=X You can tell bitcoin about its publicly reachable addresses using this option, and this can be an onion address. Given the above configuration, you can find your onion address in /var/lib/tor/bitcoin-service/hostname. For connections coming from unroutable addresses (such as 127.0.0.1, where the Tor proxy typically runs), onion addresses are given preference for your node to advertise itself with.
You can set multiple local addresses with -externalip. The one that will be rumoured to a particular peer is the most compatible one and also using heuristics, e.g. the address with the most incoming connections, etc.
-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=7zvj7a2imdgkdbg4f2dryd5rgtrn7upivr5eeij4cicjh65pooxeshid.onion -listen
(obviously, replace the .onion address with your own). It should be noted that you still listen on all devices and another node could establish a clearnet connection, when knowing your address. To mitigate this, additionally bind the address of your Tor proxy:
bitcoind ... -bind=127.0.0.1:8334=onion
If you don't care too much about hiding your node, and want to be reachable on IPv4
as well, use discover instead:
bitcoind ... -discover
and open port 8333 on your firewall (or use port mapping, i.e., -natpmp).
If you only want to use Tor to reach .onion addresses, but not use it as a proxy for normal IPv4/IPv6 communication, use:
bitcoind -onion=127.0.0.1:9050 -externalip=7zvj7a2imdgkdbg4f2dryd5rgtrn7upivr5eeij4cicjh65pooxeshid.onion -discover
If you run a web service too, create a new onion service for that. Otherwise it is trivial to link them, which may reduce privacy. Onion services created automatically (as in section 2) always have only one port open.
strengthen the Bitcoin network, as nodes in this configuration (i.e. bridge nodes) increase the cost and complexity of launching eclipse and partition attacks. However, under certain conditions, an adversary that can connect to your node on multiple networks may be able to correlate those identities by observing shared runtime characteristics. It is not recommended to expose your node over multiple networks if you require unlinkability across those identities.