blog/source/_posts/tor-hidden-onion-nixos.md at 3b4b06e64b3a60d41167c830d46a8c9411379318

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Launch Tor

The first step is to bring up a Tor hidden service to get an onion address. Add the following options to configuration.nix:

  ## Tor onion
  services.tor = {
    enable = true;
    enableGeoIP = false;
    hiddenServices.myOnion = {
      version = 3;
      map = [
        {
          port = "80";
          toHost = "[::1]";
          toPort = "8080";
        }
      ];
    };
    extraConfig = 
      ''
        ClientUseIPv4 0
        ClientUseIPv6 1
        ClientPreferIPv6ORPort 1
      '';
  };

enableGeoIP is disabled as I don't need by-country statistics.
I name the service as "myOnion", so the keys will be stored in "/var/lib/tor/onion/myOnion" folder.
Set the version to 3, which is a more secure version. The most noticable difference is that the generated onion address will be 56-character long, which is much longer than v2's 16-character. Tor already defaults to v3 since 0.3.5, but I set it just to make sure.
port is to set the port number that the hidden service binds to. Recommend to set it to port 80.

If you set it to "1234", visitor needs to specify the port number to browse your site, e.g. http://foobar.onion:1234
There is no need to grant CAP_NET_BIND_SERVICE capability nor open port 80. Tor has NAT traversal capability and can function without opening any inbound port.

toHost is location of your web server. In my case, it is the IPv6 loopback [::1]. If your server supports IPv4 (mine doesn't), you can set it to "127.0.0.1" or "localhost". If it's an IPv6 address, you need to wrap the address with square brackets [].

You can even set your domain here and skip the rest of the sections. However, this can double the latency, especially if the website is behind a CDN. Tor recommends to have a separate web server that is dedicated for Tor hidden service only. The next section shows how to set up the web server.

toPort is the port number that your web server listens to.
extraConfig is optional. The options I use here are only applicable if the server is IPv6 only.

Run # nixos-rebuild switch and three important files will be generated in the "/var/lib/tor/onion/myOnion" folder.

hostname your unique onion address, note this down. The address is derived from the private key.
hs_ed25519_public_key ED25519 elliptic-curve public key. Backup this key.
hs_ed25519_private_key Absolutely backup this key and protect it with your own life. Losing this file means losing the onion address.

Backup the keys. If you migrate to another server, you just need to move the keys, Tor will generate the same hostname from the private key.

caddyTor.nix

I set up another Caddy-powered reverse proxy which is separate from the {% post_link caddy-nixos-part-3 "mdleom.com's" %}. It's similar to caddyProxy.nix, except I replace "caddyProxy" with "caddyTor". This Nix file exposes services.caddyTor so that I can enable the Tor-related Caddy service from "configuration.nix".

{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.services.caddyTor;
in {
  options.services.caddyTor = {
    enable = mkEnableOption "Caddy web server";

    config = mkOption {
      default = "/etc/caddy/caddyTor.conf";
      type = types.str;
      description = "Path to Caddyfile";
    };

    dataDir = mkOption {
      default = "/var/lib/caddyTor";
      type = types.path;
      description = ''
        The data directory, for storing certificates. Before 17.09, this
        would create a .caddy directory. With 17.09 the contents of the
        .caddy directory are in the specified data directory instead.
      '';
    };

    package = mkOption {
      default = pkgs.caddy;
      defaultText = "pkgs.caddy";
      type = types.package;
      description = "Caddy package to use.";
    };
  };

  config = mkIf cfg.enable {
    systemd.services.caddyTor = {
      description = "Caddy web server";
      after = [ "network-online.target" ];
      wantedBy = [ "multi-user.target" ];
      environment = mkIf (versionAtLeast config.system.stateVersion "17.09")
        { CADDYPATH = cfg.dataDir; };
      serviceConfig = {
        ExecStart = ''
          ${cfg.package}/bin/caddy -root=/var/tmp -conf=${cfg.config}
        '';
        ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
        Type = "simple";
        User = "caddyTor";
        Group = "caddyTor";
        Restart = "on-failure";
        StartLimitInterval = 86400;
        StartLimitBurst = 5;
        NoNewPrivileges = true;
        LimitNPROC = 64;
        LimitNOFILE = 1048576;
        PrivateTmp = true;
        PrivateDevices = true;
        ProtectHome = true;
        ProtectSystem = "full";
        ReadWriteDirectories = cfg.dataDir;
      };
    };
    
    users.users.caddyTor = {
      home = cfg.dataDir;
      createHome = true;
    };
    
    users.groups.caddyTor = {
      members = [ "caddyTor" ];
    };
  };
}

File ownership and permissions

After you save the file to /etc/caddy/CaddyTor.nix, remember to restrict it to root.

# chown root:root /etc/caddy/caddyTor.nix
# chown 600 /etc/caddy/caddyTor.nix

caddyFile

Create a new caddyFile in /etc/caddy/caddyTor.conf and starts with the following config:

xw226dvxac7jzcpsf4xb64r4epr6o5hgn46dxlqk7gnjptakik6xnzqd.onion:8080 {
  bind ::1

  tls off

  header / {
    -strict-transport-security
  }
}

Update the onion address to the value shown in "/var/lib/tor/onion/myOnion/hostname". tls (HTTPS) is disabled here because it's not necessary as Tor hidden service already encrypts the traffic. Let's Encrypt doesn't support validating a .onion address. The only way is to purchase the cert from Digicert. Since HTTPS is not enabled, strict-transport-security (HSTS) no longer applies and the header needs to be removed to prevent the browser from attempting to connect to https://. It binds to loopback so it only listens to localhost.

The rest are similar to "caddyProxy.conf".

(removeHeaders) {
  header_upstream -cookie
  header_upstream -referer
  header_upstream -cf-ipcountry
  header_upstream -cf-connecting-ip
  header_upstream -x-forwarded-for
  header_upstream -x-forwarded-proto
  header_upstream -cf-ray
  header_upstream -cf-visitor
  header_upstream -true-client-ip
  header_upstream -cdn-loop
  header_upstream -cf-request-id
  header_upstream -cf-cache-status
}

(staticallyCfg) {
  header_upstream Host cdn.statically.io
}

# Tor onion
xw226dvxac7jzcpsf4xb64r4epr6o5hgn46dxlqk7gnjptakik6xnzqd.onion:8080 {
  bind ::1

  tls off

  header / {
    -server
    -alt-svc
    -cdn-cache
    -cdn-cachedat
    -cdn-edgestorageid
    -cdn-pullzone
    -cdn-requestcountrycode
    -cdn-requestid
    -cdn-uid
    -cf-cache-status
    -cf-ray
    -cf-request-id
    -etag
    -set-cookie
    -strict-transport-security
    -x-bytes-saved
    -x-cache
    -x-nf-request-id
    -x-served-by
    Cache-Control "max-age=604800, public"
    Referrer-Policy "no-referrer"
  }

  header /libs {
    Cache-Control "public, max-age=31536000, immutable"
  }

  proxy /img https://cdn.statically.io/img/gitlab.com/curben/blog/raw/site {
    without /img
    import removeHeaders
    import staticallyCfg
  }

  rewrite /screenshot {
    r (.*)
    to /screenshot{1}?mobile=true
  }

  proxy /screenshot https://cdn.statically.io/screenshot/curben.netlify.app {
    without /screenshot
    import removeHeaders
    import staticallyCfg
  }

  proxy / https://curben.netlify.app {
    import removeHeaders
    header_upstream Host curben.netlify.app
  }
}

Alternate Caddyfile

There is another approach which has a much simpler Caddyfile, but it doubles the latency. I could simply reverse proxy to mdleom.com but that itself is {% post_link caddy-nixos-part-3 'also' %} a reverse proxy, so it would add one more roundtrip. But hey, if the latency doesn't faze you, why not.

This is also suitable if you have a website that you can't root access.

# Do not use this approach unless you are absolutely sure
xw226dvxac7jzcpsf4xb64r4epr6o5hgn46dxlqk7gnjptakik6xnzqd.onion:8080 {
  bind ::1

  tls off

  header / {
    -strict-transport-security
  }

  proxy / https://mdleom.com {
    header_upstream Host mdleom.com
  }
}

Launch Caddy

Start the Caddy service.

  require = [ /etc/caddy/caddyProxy.nix /etc/caddy/caddyTor.nix ];
  services.caddyTor = {
    enable = true;
    config = "/etc/caddy/caddyTor.conf";
  };

Tor hidden service needs some time to announce to the Tor network, wait for a few hours before trying your newfangled onion address.

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