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Onion services

Serving Mastodon through Tor onion services.

Mastodon can be served through Tor as an onion service. This will give you a *.onion address that can only be used while connected to the Tor network.

Installing Tor

First Tor’s Debian archive needs to be added to apt.

deb https://deb.torproject.org/torproject.org stretch main
deb-src https://deb.torproject.org/torproject.org stretch main

Next add the gpg key.

curl https://deb.torproject.org/torproject.org/A3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89.asc | gpg --import
gpg --export A3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89 | apt-key add -

Finally install the required packages.

apt install tor deb.torproject.org-keyring

Configure Tor

Edit the file at /etc/tor/torrc and add the following configuration.

HiddenServiceDir /var/lib/tor/onion_service/
HiddenServiceVersion 3
HiddenServicePort 80 127.0.0.1:80

Restart Tor.

sudo service tor restart

You can now find your Tor hostname in /var/lib/tor/hidden_service/hostname.

Move your Mastodon configuration

We will need to tell Nginx about your Mastodon configuration twice. To keep things “DRY” we need to move the Mastodon configuration into its own file that can we can refer to later.

Create a new file at /etc/nginx/snippets/mastodon.conf. Copy every Mastodon configuration parameter, apart from the listen, server_name, include directives, as well as all the SSL options. Include an Onion-Location header to let supporting browsers know that this service is also accessible from Tor. Your new file should look somewhat like this:

add_header Referrer-Policy "same-origin";
add_header Onion-Location mastodon.qKnFwnNH2oH4QhQ7CoRf7HYj8wCwpDwsa8ohJmcPG9JodMZvVA6psKq7qKnFwnNH2oH4QhQ7CoRf7HYj8wCwpDwsa8ohJmcPG9JodMZvVA6psKq7.onion$request_uri;

keepalive_timeout    70;
sendfile             on;
client_max_body_size 80m;

root /home/mastodon/live/public;

# …

error_page 500 501 502 503 504 /500.html;

access_log /var/log/nginx/mastodon_access.log;
error_log /var/log/nginx/mastodon_error.log warn;

In the new configuration file, add an include directive in the place of where your Mastodon configurations were.

Your Nginx configuration file should now look a bit like this:

server {
  listen 80;
  server_name mastodon.example.com;
  return 301 https://$server_name$request_uri;
}

map $http_upgrade $connection_upgrade {
  default upgrade;
  ''      close;
}

server {
  listen 443 ssl http2;
  list [::]:443 ssl http2;
  server_name mastodon.example.com;
  include /etc/nginx/snippets/mastodon.conf;

  ssl_certificate /etc/letsencrypt/live/mastodon.example.com/fullchain.pem;
  ssl_certificate_key /etc/letsencrypt/live/mastodon.example.com/privkey.pem;
}

Serve Tor over http

This section assumes that you want to expose your instance on both Tor and the public Internet simultaneously.

While it may be tempting to serve your Tor version of Mastodon over HTTPS, it isn’t always ideal. They are mostly useful for large companies that can produce their own certificates with their own company information. There is no Certificate Authority (CA) that provides them for free, and there is also a blog post from the Tor Project explains why HTTPS certificates are not really beneficial for security. On the other hand, however, Mastodon uses a lot of redirects to the HTTPS version of your site, where the presence of a validated certificate may make it easier for your users to use your instance on Tor without having to manually remove the https:// prefix in URLs.

In this section, we will go over how to serve your Mastodon instance over HTTP, but for Tor only. This can be added by prepending an additional configuration to your existing Nginx configuration.

server {
  listen 80;
  server_name mastodon.qKnFwnNH2oH4QhQ7CoRf7HYj8wCwpDwsa8ohJmcPG9JodMZvVA6psKq7qKnFwnNH2oH4QhQ7CoRf7HYj8wCwpDwsa8ohJmcPG9JodMZvVA6psKq7.onion;
  include /etc/nginx/snippets/mastodon.conf;
}

server {
  listen 80;
  server_name mastodon.example.com;
  return 301 https://$server_name$request_uri;
}

map $http_upgrade $connection_upgrade {
  default upgrade;
  ''      close;
}

server {
  listen 443 ssl http2;
  list [::]:443 ssl http2;
  server_name mastodon.example.com;
  include /etc/nginx/snippets/mastodon.conf;

  ssl_certificate /etc/letsencrypt/live/mastodon.example.com/fullchain.pem;
  ssl_certificate_key /etc/letsencrypt/live/mastodon.example.com/privkey.pem;
}

Replace the long hash provided here with your Tor domain located in the file at /var/lib/tor/hidden_service/hostname. This should also be reflected in the Onion-Location header in the snippets file.

Note that the onion hostname has been prefixed with “mastodon.”. Your Tor address acts as a wildcard domain. All subdomains will be routed through, and you can configure Nginx to respond to any subdomain you wish. If you do not wish to host any other services on your tor address you can omit the subdomain, or choose a different subdomain.

Here you can see the payoff of moving your mastodon configurations to a different file. Without this, all of your configurations would have to be copied to both places. Any change to your configuration would have to be made in both places.

Restart your web server.

service nginx restart

Gotchas

There are a few things you will need to be aware of.

  • As mentioned earlier, certain URLs in the Mastodon frontend will force your users to a HTTPS URL. They will have to manually replace the URL with HTTP to continue.
  • Various resources, such as images, will still be offered through your regular clearnet domain. This could possibly be a problem, depending on how cautious your users want, try or need to be.

Last updated January 25, 2024 · Improve this page
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