Inside Bitcoin

1# TOR SUPPORT IN BITCOIN
2
3It is possible to run Bitcoin Core as a Tor onion service, and connect to such services.
4
5The 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.
6## Compatibility
7
8- Starting with version 22.0, Bitcoin Core only supports Tor version 3 hidden
9  services (Tor v3). Tor v2 addresses are ignored by Bitcoin Core and neither
10  relayed nor stored.
11
12- Tor removed v2 support beginning with version 0.4.6.
13
14- Bitcoin Core 31.0 removed `tor` as a network name. Use `onion` instead,
15  as in `-onlynet=onion` or `-proxy=addr:port=onion`
16  ([#34031](https://github.com/bitcoin/bitcoin/pull/34031)).
17  The `-debug=tor` logging category is unaffected.
18
19## How to see information about your Tor configuration via Bitcoin Core
20
21There are several ways to see your local onion address in Bitcoin Core:
22- in the "Local addresses" output of CLI `-netinfo`
23- in the "localaddresses" output of RPC `getnetworkinfo`
24- in the debug log (grep for "AddLocal"; the Tor address ends in `.onion`)
25
26You may set the `-debug=tor` config logging option to have additional
27information in the debug log about your Tor configuration.
28
29CLI `-addrinfo` returns the number of addresses known to your node per
30network. This can be useful to see how many onion peers your node knows,
31e.g. for `-onlynet=onion`.
32
33You can use the `getnodeaddresses` RPC to fetch a number of onion peers known to your node; run `bitcoin-cli help getnodeaddresses` for details.
34
35`bitcoin rpc` can also be substituted for `bitcoin-cli`.
36
37## 1. Run Bitcoin Core behind a Tor proxy
38
39The first step is running Bitcoin Core behind a Tor proxy. This will already anonymize all
40outgoing connections, but more is possible.
41
42    -proxy=ip[:port]
43        Set the proxy server. It will be used to try to reach .onion addresses
44        as well. You need to use -noonion or -onion=0 to explicitly disable
45        outbound access to onion services.
46
47    -proxy=ip[:port]=onion
48    or
49    -onion=ip[:port]
50        Set the proxy server for reaching .onion addresses. You do not need to
51        set this if it's the same as the generic -proxy. You can use -onion=0 to
52        explicitly disable access to onion services.
53        ------------------------------------------------------------------------
54        Note: The proxy for DNS requests is taken from
55        -proxy=addr:port or
56        -proxy=addr:port=ipv4 or
57        -proxy=addr:port=ipv6
58        (last one if multiple options are given). It is not taken from
59        -proxy=addr:port=onion or
60        -onion=addr:port.
61        If no proxy for DNS requests is configured, then they will be done using
62        the functions provided by the operating system, most likely resulting in
63        them being done over the clearnet to the DNS servers of the internet
64        service provider.
65        ------------------------------------------------------------------------
66
67If -proxy or -onion is specified multiple times, later occurrences override
68earlier ones and command line overrides the config file. UNIX domain sockets may
69be used for proxy connections. Set `-onion` or `-proxy` to the local socket path
70with the prefix `unix:` (e.g. `-onion=unix:/home/me/torsocket`).
71
72    -listen
73        When using -proxy, listening is disabled by default. If you want to
74        manually configure an onion service (see section 3), you'll need to
75        enable it explicitly.
76
77    -connect=X
78    -addnode=X
79    -seednode=X
80        When behind a Tor proxy, you can specify .onion addresses instead of IP
81        addresses or hostnames in these parameters. Such addresses can also be
82        exchanged with other P2P nodes.
83
84    -onlynet=onion
85        Make automatic outbound connections only to .onion addresses. Inbound
86        and manual connections are not affected by this option. It can be
87        specified multiple times to allow multiple networks, e.g. onlynet=onion,
88        onlynet=i2p, onlynet=cjdns.
89
90In a typical situation, this suffices to run behind a Tor proxy:
91
92    bitcoind -proxy=127.0.0.1:9050
93
94`bitcoin node` or `bitcoin gui` can also be substituted for `bitcoind`.
95
96## 2. Automatically create a Bitcoin Core onion service
97
98Bitcoin Core makes use of Tor's control socket API to create and destroy
99ephemeral onion services programmatically. This means that if Tor is running and
100proper authentication has been configured, Bitcoin Core automatically creates an
101onion service to listen on. The goal is to increase the number of available
102onion nodes.
103
104This feature is enabled by default if Bitcoin Core is listening (`-listen`) and
105it requires a Tor connection to work. It can be explicitly disabled with
106`-listenonion=0`. If it is not disabled, it can be configured using the
107`-torcontrol` and `-torpassword` settings.
108
109To see verbose Tor information in the bitcoind debug log, pass `-debug=tor`.
110
111### Control Port
112
113You may need to set up the Tor Control Port. On Linux distributions there may be
114some or all of the following settings in `/etc/tor/torrc`, generally commented
115out by default (if not, add them):
116
117```
118ControlPort 9051
119CookieAuthentication 1
120CookieAuthFileGroupReadable 1
121DataDirectoryGroupReadable 1
122```
123
124Add or uncomment those, save, and restart Tor (usually `systemctl restart tor`
125or `sudo systemctl restart tor` on most systemd-based systems, including recent
126Debian and Ubuntu, or just restart the computer).
127
128### Authentication
129
130Connecting to Tor's control socket API requires one of two authentication
131methods to be configured: cookie authentication or bitcoind's `-torpassword`
132configuration option.
133
134#### Cookie authentication
135
136For cookie authentication, the user running bitcoind must have read access to
137the `CookieAuthFile` specified in the Tor configuration. In some cases this is
138preconfigured and the creation of an onion service is automatic. Don't forget to
139use the `-debug=tor` bitcoind configuration option to enable Tor debug logging.
140
141If a permissions problem is seen in the debug log, e.g. `tor: Authentication
142cookie /run/tor/control.authcookie could not be opened (check permissions)`, it
143can be resolved by adding both the user running Tor and the user running
144bitcoind to the same Tor group and setting permissions appropriately.
145
146On Debian-derived systems, the Tor group will likely be `debian-tor` and one way
147to verify could be to list the groups and grep for a "tor" group name:
148
149```
150getent group | cut -d: -f1 | grep -i tor
151```
152
153You can also check the group of the cookie file. On most Linux systems, the Tor
154auth cookie will usually be `/run/tor/control.authcookie`:
155
156```
157TORGROUP=$(stat -c '%G' /run/tor/control.authcookie)
158```
159
160Once you have determined the `${TORGROUP}` and selected the `${USER}` that will
161run bitcoind, run this as root:
162
163```
164usermod -a -G ${TORGROUP} ${USER}
165```
166
167Then restart the computer (or log out) and log in as the `${USER}` that will run
168bitcoind.
169
170#### `torpassword` authentication
171
172For the `-torpassword=password` option, the password is the clear text form that
173was used when generating the hashed password for the `HashedControlPassword`
174option in the Tor configuration file.
175
176The hashed password can be obtained with the command `tor --hash-password
177password` (refer to the [Tor Dev
178Manual](https://2019.www.torproject.org/docs/tor-manual.html.en) for more
179details).
180
181
182## 3. Manually create a Bitcoin Core onion service
183
184You can also manually configure your node to be reachable from the Tor network.
185Add these lines to your `/etc/tor/torrc` (or equivalent config file):
186
187    HiddenServiceDir /var/lib/tor/bitcoin-service/
188    HiddenServicePort 8333 127.0.0.1:8334
189    # If `tor --list-modules` shows "pow: yes", then enable PoW protection.
190    # It is available in tor-0.4.8.1-alpha and newer when configured with
191    # `./configure --enable-gpl`.
192    HiddenServicePoWDefensesEnabled 1
193
194The directory can be different of course, but virtual port numbers should be equal to
195your bitcoind's P2P listen port (8333 by default), and target addresses and ports
196should be equal to binding address and port for inbound Tor connections (127.0.0.1:8334 by default).
197
198    -externalip=X   You can tell bitcoin about its publicly reachable addresses using
199                    this option, and this can be an onion address. Given the above
200                    configuration, you can find your onion address in
201                    /var/lib/tor/bitcoin-service/hostname. For connections
202                    coming from unroutable addresses (such as 127.0.0.1, where the
203                    Tor proxy typically runs), onion addresses are given
204                    preference for your node to advertise itself with.
205
206                    You can set multiple local addresses with -externalip. The
207                    one that will be rumoured to a particular peer is the most
208                    compatible one and also using heuristics, e.g. the address
209                    with the most incoming connections, etc.
210
211    -listen         You'll need to enable listening for incoming connections, as this
212                    is off by default behind a proxy.
213
214    -discover       When -externalip is specified, no attempt is made to discover local
215                    IPv4 or IPv6 addresses. If you want to run a dual stack, reachable
216                    from both Tor and IPv4 (or IPv6), you'll need to either pass your
217                    other addresses using -externalip, or explicitly enable -discover.
218                    Note that both addresses of a dual-stack system may be easily
219                    linkable using traffic analysis.
220
221In a typical situation, where you're only reachable via Tor, this should suffice:
222
223    bitcoind -proxy=127.0.0.1:9050 -externalip=7zvj7a2imdgkdbg4f2dryd5rgtrn7upivr5eeij4cicjh65pooxeshid.onion -listen
224
225(obviously, replace the .onion address with your own). It should be noted that you still
226listen on all devices and another node could establish a clearnet connection, when knowing
227your address. To mitigate this, additionally bind the address of your Tor proxy:
228
229    bitcoind ... -bind=127.0.0.1:8334=onion
230
231If you don't care too much about hiding your node, and want to be reachable on IPv4
232as well, use `discover` instead:
233
234    bitcoind ... -discover
235
236and open port 8333 on your firewall (or use port mapping, i.e., `-natpmp`).
237
238If you only want to use Tor to reach .onion addresses, but not use it as a proxy
239for normal IPv4/IPv6 communication, use:
240
241    bitcoind -onion=127.0.0.1:9050 -externalip=7zvj7a2imdgkdbg4f2dryd5rgtrn7upivr5eeij4cicjh65pooxeshid.onion -discover
242
243## 4. Privacy recommendations
244
245- Do not add anything but Bitcoin Core ports to the onion service created in section 3.
246  If you run a web service too, create a new onion service for that.
247  Otherwise it is trivial to link them, which may reduce privacy. Onion
248  services created automatically (as in section 2) always have only one port
249  open.
250- Operating a node that listens on multiple networks (e.g. IPv4 and Tor) can help