Tor Support in Zcash

Warning: Do not assume Tor support does the correct thing in Zcash; better Tor support is a future feature goal.

It is possible to run Zcash 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 port 9150. See Tor Project FAQ:TBBSocksPort for how to properly configure Tor.

1. Run Zcash behind a Tor proxy

The first step is running Zcash behind a Tor proxy. This will already make all outgoing connections be anonymized, but more is possible.

Set the proxy server. If SOCKS5 is selected (default), this proxy server will be used to try to reach .onion addresses as well.
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.
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, -addnode=X, -seednode=X
When behind a Tor proxy, you can specify .onion addresses instead of IP addresses or hostnames in these parameters. It requires 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:

$ zcashd -proxy=

2. Run a Zcash 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/zcash-service/ HiddenServicePort 8233 HiddenServicePort 18233

The directory can be different of course, but (both) port numbers should be equal to your zcashd’s P2P listen port (8233 by default).

You can tell Zcash 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/zcash-service/hostname. Onion addresses are given preference for your node to advertize itself with, for connections coming from unroutable addresses (such as, where the Tor proxy typically runs).
You’ll need to enable listening for incoming connections, as this is off by default behind a proxy.
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:

$ zcashd -proxy= -externalip=zctestseie6wxgio.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:

$ zcashd ... -bind=

If you don’t care too much about hiding your node, and want to be reachable on IPv4 as well, use discover instead:

$ zcashd ... -discover

and open port 8233 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:

$ zcashd -onion= -externalip=zctestseie6wxgio.onion -discover

3. Automatically listen on Tor

Starting with Tor version it is possible, through Tor’s control socket API, to create and destroy ‘ephemeral’ hidden services programmatically. Zcash has been updated to make use of this.

This means that if Tor is running (and proper authentication has been configured), Zcash automatically creates a hidden service to listen on. Zcash will also use Tor automatically to connect to other .onion nodes if the control socket can be successfully opened. This will positively affect the number of available .onion nodes and their usage.

This new feature is enabled by default if Zcash is listening (-listen), and requires a Tor connection to work. It can be explicitly disabled with -listenonion=0 and, if not disabled, configured using the -torcontrol and -torpassword settings. To show verbose debugging information, pass -debug=tor.

Connecting to Tor’s control socket API requires one of two authentication methods to be configured. For cookie authentication the user running zcashd must have write access to the CookieAuthFile specified in Tor configuration. In some cases this is preconfigured and the creation of a hidden service is automatic. If permission problems are seen with -debug=tor they can be resolved by adding both the user running tor and the user running zcashd to the same group and setting permissions appropriately. On Debian-based systems the user running zcashd can be added to the debian-tor group, which has the appropriate permissions. An alternative authentication method is the use of the -torpassword flag and a hash-password which can be enabled and specified in Tor configuration.

4. Connect to a Zcash hidden server

To test your set-up, you might want to try connecting via Tor on a different computer to just a a single Zcash hidden server. Launch zcashd as follows:

$ zcashd -onion= -connect=zctestseie6wxgio.onion

Now use zcash-cli to verify there is only a single peer connection.

$ zcash-cli getpeerinfo
        "id" : 1,
        "addr" : "zctestseie6wxgio.onion:18233",
        "version" : 170002,
        "subver" : "/MagicBean:1.0.0/",

To connect to multiple Tor nodes, use:

$ zcashd -onion= -addnode=zctestseie6wxgio.onion -dnsseed=0 -onlynet=onion