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. See [Tor Project FAQ:TBBSocksPort](https://www.torproject.org/docs/faq.html.en#TBBSocksPort) for how to properly 6configure Tor. 7 8## How to see information about your Tor configuration via Bitcoin Core 9 10There are several ways to see your local onion address in Bitcoin Core: 11- in the debug log (grep for "tor:" or "AddLocal") 12- in the output of RPC `getnetworkinfo` in the "localaddresses" section 13- in the output of the CLI `-netinfo` peer connections dashboard 14 15You may set the `-debug=tor` config logging option to have additional 16information in the debug log about your Tor configuration. 17 18 19## 1. Run Bitcoin Core behind a Tor proxy 20 21The first step is running Bitcoin Core behind a Tor proxy. This will already anonymize all 22outgoing connections, but more is possible. 23 24 -proxy=ip:port Set the proxy server. If SOCKS5 is selected (default), this proxy 25 server will be used to try to reach .onion addresses as well. 26 27 -onion=ip:port Set the proxy server to use for Tor onion services. You do not 28 need to set this if it's the same as -proxy. You can use -noonion 29 to explicitly disable access to onion services. 30 31 -listen When using -proxy, listening is disabled by default. If you want 32 to run an onion service (see next section), you'll need to enable 33 it explicitly. 34 35 -connect=X When behind a Tor proxy, you can specify .onion addresses instead 36 -addnode=X of IP addresses or hostnames in these parameters. It requires 37 -seednode=X SOCKS5. In Tor mode, such addresses can also be exchanged with 38 other P2P nodes. 39 40 -onlynet=onion Make outgoing connections only to .onion addresses. Incoming 41 connections are not affected by this option. This option can be 42 specified multiple times to allow multiple network types, e.g. 43 ipv4, ipv6, or onion. 44 45In a typical situation, this suffices to run behind a Tor proxy: 46 47 ./bitcoind -proxy=127.0.0.1:9050 48 49 50## 2. Run a Bitcoin Core hidden server 51 52If you configure your Tor system accordingly, it is possible to make your node also 53reachable from the Tor network. Add these lines to your /etc/tor/torrc (or equivalent 54config file): *Needed for Tor version 0.2.7.0 and older versions of Tor only. For newer 55versions of Tor see [Section 3](#3-automatically-listen-on-tor).* 56 57 HiddenServiceDir /var/lib/tor/bitcoin-service/ 58 HiddenServicePort 8333 127.0.0.1:8334 59 HiddenServicePort 18333 127.0.0.1:18334 60 61The directory can be different of course, but virtual port numbers should be equal to 62your bitcoind's P2P listen port (8333 by default), and target addresses and ports 63should be equal to binding address and port for inbound Tor connections (127.0.0.1:8334 by default). 64 65 -externalip=X You can tell bitcoin about its publicly reachable addresses using 66 this option, and this can be an onion address. Given the above 67 configuration, you can find your onion address in 68 /var/lib/tor/bitcoin-service/hostname. For connections 69 coming from unroutable addresses (such as 127.0.0.1, where the 70 Tor proxy typically runs), onion addresses are given 71 preference for your node to advertise itself with. 72 73 You can set multiple local addresses with -externalip. The 74 one that will be rumoured to a particular peer is the most 75 compatible one and also using heuristics, e.g. the address 76 with the most incoming connections, etc. 77 78 -listen You'll need to enable listening for incoming connections, as this 79 is off by default behind a proxy. 80 81 -discover When -externalip is specified, no attempt is made to discover local 82 IPv4 or IPv6 addresses. If you want to run a dual stack, reachable 83 from both Tor and IPv4 (or IPv6), you'll need to either pass your 84 other addresses using -externalip, or explicitly enable -discover. 85 Note that both addresses of a dual-stack system may be easily 86 linkable using traffic analysis. 87 88In a typical situation, where you're only reachable via Tor, this should suffice: 89 90 ./bitcoind -proxy=127.0.0.1:9050 -externalip=7zvj7a2imdgkdbg4f2dryd5rgtrn7upivr5eeij4cicjh65pooxeshid.onion -listen 91 92(obviously, replace the .onion address with your own). It should be noted that you still 93listen on all devices and another node could establish a clearnet connection, when knowing 94your address. To mitigate this, additionally bind the address of your Tor proxy: 95 96 ./bitcoind ... -bind=127.0.0.1 97 98If you don't care too much about hiding your node, and want to be reachable on IPv4 99as well, use `discover` instead: 100 101 ./bitcoind ... -discover 102 103and open port 8333 on your firewall (or use -upnp). 104 105If you only want to use Tor to reach .onion addresses, but not use it as a proxy 106for normal IPv4/IPv6 communication, use: 107 108 ./bitcoind -onion=127.0.0.1:9050 -externalip=7zvj7a2imdgkdbg4f2dryd5rgtrn7upivr5eeij4cicjh65pooxeshid.onion -discover 109 110## 3. Automatically listen on Tor 111 112Starting with Tor version 0.2.7.1 it is possible, through Tor's control socket 113API, to create and destroy 'ephemeral' onion services programmatically. 114Bitcoin Core has been updated to make use of this. 115 116This means that if Tor is running (and proper authentication has been configured), 117Bitcoin Core automatically creates an onion service to listen on. This will positively 118affect the number of available .onion nodes. 119 120This new feature is enabled by default if Bitcoin Core is listening (`-listen`), and 121requires a Tor connection to work. It can be explicitly disabled with `-listenonion=0` 122and, if not disabled, configured using the `-torcontrol` and `-torpassword` settings. 123To show verbose debugging information, pass `-debug=tor`. 124 125Connecting to Tor's control socket API requires one of two authentication methods to be 126configured. It also requires the control socket to be enabled, e.g. put `ControlPort 9051` 127in `torrc` config file. For cookie authentication the user running bitcoind must have read 128access to the `CookieAuthFile` specified in Tor configuration. In some cases this is 129preconfigured and the creation of an onion service is automatic. If permission problems 130are seen with `-debug=tor` they can be resolved by adding both the user running Tor and 131the user running bitcoind to the same group and setting permissions appropriately. On 132Debian-based systems the user running bitcoind can be added to the debian-tor group, 133which has the appropriate permissions. Before starting bitcoind you will need to re-login 134to allow debian-tor group to be applied. Otherwise you will see the following notice: "tor: 135Authentication cookie /run/tor/control.authcookie could not be opened (check permissions)" 136on debug.log. 137 138An alternative authentication method is the use 139of the `-torpassword=password` option. The `password` is the clear text form that 140was used when generating the hashed password for the `HashedControlPassword` option 141in the tor configuration file. The hashed password can be obtained with the command 142`tor --hash-password password` (read the tor manual for more details). 143 144## 4. Privacy recommendations 145 146- Do not add anything but Bitcoin Core ports to the onion service created in section 2. 147 If you run a web service too, create a new onion service for that. 148 Otherwise it is trivial to link them, which may reduce privacy. Hidden 149 services created automatically (as in section 3) always have only one port 150 open. 151