# Tor

Related articles

- Gnunet
- I2P
- Freenet

Tor is an open source implementation of 2nd generation onion routing that provides free access to an anonymous proxy network. Its primary goal is to enable online anonymity by protecting against traffic analysis attacks.

## Introduction

Users of the Tor network run an onion proxy on their machine. This software connects out to Tor, periodically negotiating a virtual circuit through the Tor network. Tor employs cryptography in a layered manner (hence the 'onion' analogy), ensuring perfect forward secrecy between routers. At the same time, the onion proxy software presents a SOCKS interface to its clients. SOCKS-aware applications may be pointed at Tor, which then multiplexes the traffic through a Tor virtual circuit.

Warning: Tor by itself is not all you need to maintain your anonymity. There are several major pitfalls to watch out for (see: Want Tor to really work?).

Through this process the onion proxy manages networking traffic for end-user anonymity. It keeps a user anonymous by encrypting traffic, sending it through other nodes of the Tor network, and decrypting it at the last node to receive your traffic before forwarding it to the server you specified. One trade off that has to be made for the anonymity Tor provides is that it can be considerably slower than a regular direct connection, due to the large amount of traffic re-routing. Additionally, although Tor provides protection against traffic analysis it cannot prevent traffic confirmation at the boundaries of the Tor network (i.e. the traffic entering and exiting the network).

## Installation

Install tor, available in the official repositories.

Additionally, there is a Qt frontend for Tor in package vidalia. In addition to controlling the Tor process, Vidalia allows you to view and configure the status of Tor, monitor bandwidth usage, and view, filter, and search log messages.

## Configuration

To get a better understanding of Tor review the `/etc/tor/torrc` configuration file. The configuration options are explained in `man tor` and the Tor website. The default configuration should work fine for most Tor users.

You can set custom file descriptor ulimits for Tor in `/etc/conf.d/tor` using the `TOR_MAX_FD` variable. This sets a limit on the maximum number of open files.

By default Tor logs to stdout with a log-level of "notice". If system logging is enabled in the `torrc` configuration file, it will default to `/usr/local/var/log/tor/`.

The "RunAsDaemon" setting conflicts with the default runtype of "simple" in the service file. You should not need to enable it. systemd handles the daemonization of tor. If you do enable it for whatever reason, you will need to override the service file to change the runtype to "Type=forking" so systemd allows tor to fork itself.

## Running Tor in a Chroot

For security purposes, it may be desirable to run Tor in a chroot. The following script will create an appropriate chroot in /opt/torchroot:

    ~/torchroot-setup.sh

    #!/bin/bash
    export TORCHROOT=/opt/torchroot

    mkdir -p $TORCHROOT
    mkdir -p $TORCHROOT/etc/tor
    mkdir -p $TORCHROOT/dev
    mkdir -p $TORCHROOT/usr/bin
    mkdir -p $TORCHROOT/usr/lib
    mkdir -p $TORCHROOT/usr/share/tor
    mkdir -p $TORCHROOT/var/lib

    ln -s /usr/lib  $TORCHROOT/lib
    cp /etc/hosts           $TORCHROOT/etc/
    cp /etc/host.conf       $TORCHROOT/etc/
    cp /etc/localtime       $TORCHROOT/etc/
    cp /etc/nsswitch.conf   $TORCHROOT/etc/
    cp /etc/resolv.conf     $TORCHROOT/etc/
    cp /etc/tor/torrc       $TORCHROOT/etc/tor/

    cp /usr/bin/tor         $TORCHROOT/usr/bin/
    cp /usr/share/tor/geoip* $TORCHROOT/usr/share/tor/
    cp /lib/libnss* /lib/libnsl* /lib/ld-linux.so* /lib/libresolv* /lib/libgcc_s.so* $TORCHROOT/usr/lib/
    cp $(ldd /usr/bin/tor | awk '{print $3}'|grep --color=never "^/") $TORCHROOT/usr/lib/
    cp -r /var/lib/tor      $TORCHROOT/var/lib/
    chown -R tor:tor $TORCHROOT/var/lib/tor

    sh -c "grep --color=never ^tor /etc/passwd > $TORCHROOT/etc/passwd"
    sh -c "grep --color=never ^tor /etc/group > $TORCHROOT/etc/group"

    mknod -m 644 $TORCHROOT/dev/random c 1 8
    mknod -m 644 $TORCHROOT/dev/urandom c 1 9
    mknod -m 666 $TORCHROOT/dev/null c 1 3

    if [[ "$(uname -m)" == "x86_64" ]]; then
      cp /usr/lib/ld-linux-x86-64.so* $TORCHROOT/usr/lib/.
      ln -sr /usr/lib64 $TORCHROOT/lib64
      ln -s $TORCHROOT/usr/lib ${TORCHROOT}/usr/lib64
    fi

After running the script as root, Tor can be launched in the chroot with the command: `# chroot --userspec=tor:tor /opt/torchroot /usr/bin/tor`

## Usage

Start/enable `tor.service` using systemd.

Alternatively, you can launch it from the vidalia interface.

To use a program over tor, configure it to use 127.0.0.1 or localhost as a SOCKS5 proxy, with port 9050 (plain tor with standard settings) or port 9051 (configuration with vidalia, standard settings). To check if Tor is functioning properly visit the Tor, Harvard or Xenobite.eu websites.

## Web browsing

The Tor Project currently only supports web browsing with tor through the Tor Browser Bundle, which can be downloaded from the AUR. It is built with a patched version of the Firefox extended support releases. Tor can also be used with regular Firefox, Chromium and other browsers, but this is not recommended by the Tor Project.

Tip: For makepkg to verify the signature on the AUR source tarball download for TBB, signing keys from the Tor Project (currently 0x63FEE659) must be downloaded from the keyservers and added to the user gpg keyring with:

    $ gpg --recv-keys 0x63FEE659

### Firefox

In Preferences > Advanced > Network tab > Settings manually set Firefox to use the SOCKS proxy `localhost` with port `9050`. Then you must type `about:config` into the address bar and void your warranty. Change `network.proxy.socks_remote_dns` to `true` and restart the browser. This channels all DNS requests through TOR's socks proxy.

### Chromium

You can simply run:

    $ chromium --proxy-server="socks://localhost:9050"

Just as with Firefox, you can setup a fast switch for example through Proxy SwitchySharp.

Once installed enter in its configuration page. Under the tab Proxy Profiles add a new profile Tor, if ticked untick the option Use the same proxy server for all protocols, then add localhost as SOCKS Host, 9050 to the respective port and select SOCKS v5.

Optionally you can enable the quick switch under the General tab to be able to switch beetween normal navigation and Tor network just by left-clicking on the Proxy SwitchySharp's icon.

### Luakit

You can simply run:

    $ torify luakit

## HTTP proxy

Tor can be used with an HTTP proxy like Polipo or Privoxy, however the Tor dev team recommends using the SOCKS5 library since browsers directly support it.

### Firefox

The FoxyProxy add-on allows you to specify multiple proxies for different URLs or for all your browsing. After restarting Firefox manually set Firefox to port `8118` on `localhost`, which is where Polipo or Privoxy are running. These settings can be access under Add > Standard proxy type. Select a proxy label (e.g Tor) and enter the port and host into the HTTP Proxy and SSL Proxy fields. To check if Tor is functioning properly visit the Tor Check website and toggle Tor.

### Polipo

The Tor Project has created a custom Polipo configuration file to prevent potential problems with Polipo as well to provide better anonymity.

Keep in mind that Polipo is not required if you can use a SOCKS 5 proxy, which Tor starts automatically on port 9050. If you want to use Chromium with Tor, you do not need the Polipo package (see: #Chromium).

### Privoxy

You can also use this setup in other applications like messaging (e.g. Jabber, IRC). Applications that support HTTP proxies you can connect to Privoxy (i.e. `127.0.0.1:8118`). To use SOCKS proxy directly, you can point your application at Tor (i.e. `127.0.0.1:9050`). A problem with this method though is that applications doing DNS resolves by themselves may leak information. Consider using Socks4A (e.g. with Privoxy) instead.

## Instant messaging

In order to use an IM client with tor, we do not need an http proxy like polipo/privoxy. We will be using tor's daemon directly which listens to port 9050 by default.

### Pidgin

You can set up Pidgin to use Tor globally, or per account. To use Tor globally, go to Tools -> Preferences -> Proxy. To use Tor for specific accounts, go to Accounts > Manage Accounts, select the desired account, click Modify, then go to the Proxy tab. The proxy settings are as follows:

    Proxy type 	SOCKS5
    Host 	        127.0.0.1
    Port 	        9150

Note that some time in 2013 the Port has changed from 9050 to 9150 if you use the Tor Browser Bundle. Try the other value if you receive a "Connection refused" message.

## Irssi

Freenode does not recommend that you use Privoxy with Irssi. Instead they recommend using the `mapaddress` approach and running `torify irssi` to start it up. Therefore, add the following to `/etc/tor/torrc`:

    mapaddress  10.40.40.40 p4fsi4ockecnea7l.onion

Freenode requires charybdis and ircd-seven's SASL mechanism for identifying to nickserv during connection. Download `cap_sasl.pl`, which enables SASL in Irssi, from the Freenode website (i.e. http://www.freenode.net/sasl/cap_sasl.pl) and save it to `~/.irssi/scripts/cap_sasl.pl`

Then install perl-crypt-openssl-bignum, perl-crypt-blowfish and then perl-crypt-dh from the AUR.

Alternatively, you can install the modules using perl:

    $ perl -MCPAN -e 'install Crypt::OpenSSL::Bignum Crypt::DH Crypt::Blowfish'

Start irssi

    $ torify irssi

Load the script that will employ the SASL mechanism.

    /script load cap_sasl.pl

Set your identification to nickserv, which will be read when connecting. Supported mechanisms are PLAIN and DH-BLOWFISH.

    /sasl set network username password mechanism

Connect to Freenode:

    /connect -network network 10.40.40.40

For more information check Accessing freenode Via Tor and the SASL README at freenode.net or the IRC/SILC Wiki article at torproject.org.

If you are receiving errors check the Cannot Connect to Freenode IRC using Irssi & Tor thread on the Arch Linux forums.

## Pacman

Pacman download operations (repository DBs, packages, and public keys) can be done using the Tor network. Though relatively extreme, this measure is useful to prevent an adversary (most likely at one's LAN or the mirror) from knowing a subset of the packages you have installed, at the cost of longer latency, lower throughput, possible suspicion, and possible failure (if Tor is being filtered via the current connection).

Warning: It would be arguably simpler for an adversary, specifically one who desires to indiscriminately disseminate malware, to perform his/her activity by deploying malicious Tor exit node(s). Always use signed packages and verify new public keys by out-of-band means.

    /etc/pacman.conf

    ...
    XferCommand = /usr/bin/curl --socks5-hostname localhost:9050 -C - -f %u > %o
    ...

## Running a Tor server

The Tor network is reliant on people contributing bandwidth. There are several ways to contribute to the network.

### Running a Tor bridge

This involves making your machine an 'entry node' for people who are having trouble connecting to Tor through traditional methods.

#### Configuration

According to https://www.torproject.org/docs/bridges , make your torrc be just these four lines:

       SocksPort 0
       ORPort 443
       BridgeRelay 1
       Exitpolicy reject *:*

#### Troubleshooting

If you get "Could not bind to 0.0.0.0:443: Permission denied" errors on startup, you will need to pick a higher ORPort (e.g. 8080), or perhaps forward the port in your router.

### Running a "Middleman" relay

This means that your machine will contribute bandwidth to the 'internal' part of the network, acting as neither an entry nor exit point, merely forwarding bits to and from other Tor nodes/relays.

#### Configuration

You should at least share 20KiB/s:

    Nickname tornickname
    ORPort 9001
    BandwidthRate 20 KB            # Throttle traffic to 20KB/s
    BandwidthBurst 50 KB           # But allow bursts up to 50KB/s

Run Tor as middleman ( a relay):

    ExitPolicy reject *:*

### Running a Tor exit node

Any requests from a Tor user to the regular internet obviously need to exit the network somewhere, and exit nodes provide this vital service. To the accessed host, the request will appear as having originated from your machine. This means that running an exit node is generally considered more legally onerous than running other forms of Tor relays. Before becoming an exit relay, you may want to read Tips for Running an Exit Node With Minimal Harrasment.

#### Configuration

Using the torrc, you can configure which services you wish to allow through your exit node. Allow all traffic:

    ExitPolicy accept	*:*

Allow only irc ports 6660-6667 to exit from node:

    ExitPolicy accept *:6660-6667,reject *:* # Allow irc ports but no more

By default, Tor will block certain ports. You can use the torrc to overide this.

    ExitPolicy accept *:119        # Accept nntp as well as default exit policy

## TorDNS

The Tor 0.2.x series provides a built-in DNS forwarder. To enable it add the following lines to the Tor configuration file and restart the daemon:

    /etc/tor/torrc

    DNSPort 9053
    AutomapHostsOnResolve 1
    AutomapHostsSuffixes .exit,.onion

This will allow Tor to accept DNS requests (listening on port 9053 in this example) like a regular DNS server, and resolve the domain via the Tor network. A downside is that it's only able to resolve DNS queries for A-records; MX and NS queries are never answered. For more information see this Debian-based introduction.

DNS queries can also be performed through a command line interface by using `tor-resolve`. For example:

    $ tor-resolve archlinux.org
    66.211.214.131

### Using TorDNS for all DNS queries

It is possible to configure your system, if so desired, to use TorDNS for all queries your system makes, regardless of whether or not you eventually use Tor to connect to your final destination. To do this, configure your system to use 127.0.0.1 as its DNS server and edit the 'DNSPort' line in `/etc/tor/torrc` to show:

    DNSPort 53

Alternatively, you can use a local caching DNS server, such as dnsmasq or pdnsd, which will also compensate for TorDNS being a little slower than traditional DNS servers. The following instructions will show how to set up dnsmasq for this purpose.

Change the tor setting to listen for the DNS request in port 9053 and install dnsmasq.

Modify its configuration file so that it contains:

    /etc/dnsmasq.conf

    no-resolv
    server=127.0.0.1#9053
    listen-address=127.0.0.1

These configurations set dnsmasq to listen only for requests from the local computer, and to use TorDNS at its sole upstream provider. It is now neccessary to edit `/etc/resolv.conf` so that your system will query only the dnsmasq server.

    /etc/resolv.conf

    nameserver 127.0.0.1

Start the dnsmasq daemon.

Finally if you use dhcpd you would need to change its settings to that it does not alter the resolv configuration file. Just add this line in the configuration file:

    /etc/dhcpcd.conf

    nohook resolv.conf

If you already have an nohook line, just add resolv.conf separated with a comma.

## Torify

torify will allow you use an application via the Tor network without the need to make configuration changes to the application involved. From the man page:

torify is a simple wrapper that calls tsocks with a tor specific configuration file. tsocks itself is a wrapper between the tsocks library and the application that you would like to run socksified

Usage example:

    $ torify elinks checkip.dyndns.org
    $ torify wget -qO- https://check.torproject.org/ | grep -i congratulations

Torify will not, however, perform DNS lookups through the Tor network. A workaround is to use it in conjunction with `tor-resolve` (described above). In this case, the procedure for the first of the above examples would look like this:

    $ tor-resolve checkip.dyndns.org

    208.78.69.70

    $ torify elinks 208.78.69.70

## Transparent Torification

In some cases it is more secure and often easier to transparently torify an entire system instead of configuring individual applications to use Tor's socks port, not to mention preventing DNS leaks. Transparent torification can be done with iptables in such a way that all outbound packets are redirected through Tor's TransPort, except the Tor traffic itself. Once in place, applications do not need to be configured to use Tor, though Tor's SocksPort will still work. This also works for DNS via Tor's DNSPort, but realize that Tor only supports TCP, thus UDP packets other than DNS cannot be sent through Tor and therefore must be blocked entirely to prevent leaks. Using iptables to transparently torify a system affords comparatively strong leak protection, but it is not a substitute for virtualized torification applications such as Whonix, or TorVM[1]. Transparent torification also will not protect against fingerprinting attacks on its own, so it is recommended to use it in conjunction with the Tor Browser(AUR: tor-browser-en) or to use an amnesic solution like Tails instead. Applications can still learn your computer's hostname, MAC address, serial number, timezone, etc. and those with root privileges can disable the firewall entirely. In other words, transparent torification with iptables protects against accidental connections and DNS leaks by misconfigured software, it is not sufficient to protect against malware or software with serious security vulnerabilities.

To enable transparent torification, use the following file for `iptables-restore` and `ip6tables-restore` (internally used by systemd's `iptables.service` and `ip6tables.service`).

    /etc/iptables/iptables.rules

    #This file uses the nat table to force outgoing connections through the TransPort or DNSPort, and blocks anything it cannot torrify.
    #Note: Now using --ipv6 and --ipv4 for protocol specific changes. iptables-restore and ip6tables-restore can now use the same file.
    #       Where --ipv6 or --ipv4 is explicitly defined, ip*tables-restore will ignore the rule if it is not for the correct protocol.
    #Note: ip6tables does not support --reject-with
    #Make sure your torrc contains the following lines:
    #       SocksPort 9050
    #       DNSPort 5353
    #       TransPort 9040
    #See iptables(8)

    *nat
    :PREROUTING ACCEPT [6:2126]
    :INPUT ACCEPT [0:0]
    :OUTPUT ACCEPT [17:6239]
    :POSTROUTING ACCEPT [6:408]
    -A PREROUTING ! -i lo -p udp -m udp --dport 53 -j REDIRECT --to-ports 5353
    -A PREROUTING ! -i lo -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j REDIRECT --to-ports 9040
    -A OUTPUT -o lo -j RETURN
    --ipv4 -A OUTPUT -d 192.168.0.0/16 -j RETURN
    -A OUTPUT -m owner --uid-owner "tor" -j RETURN
    -A OUTPUT -p udp -m udp --dport 53 -j REDIRECT --to-ports 5353
    -A OUTPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j REDIRECT --to-ports 9040
    COMMIT

    *filter
    :INPUT DROP [0:0]
    :FORWARD DROP [0:0]
    :OUTPUT DROP [0:0]
    -A INPUT -i lo -j ACCEPT
    -A INPUT -p icmp -j ACCEPT
    -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
    --ipv4 -A INPUT -p tcp -j REJECT --reject-with tcp-reset
    --ipv4 -A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable
    --ipv4 -A INPUT -j REJECT --reject-with icmp-proto-unreachable
    --ipv6 -A INPUT -j REJECT
    --ipv4 -A OUTPUT -d 127.0.0.0/8 -j ACCEPT
    --ipv4 -A OUTPUT -d 192.168.0.0/16 -j ACCEPT
    --ipv6 -A OUTPUT -d ::1/8 -j ACCEPT
    -A OUTPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
    -A OUTPUT -m owner --uid-owner "tor" -j ACCEPT
    --ipv4 -A OUTPUT -j REJECT --reject-with icmp-port-unreachable
    --ipv6 -A OUTPUT -j REJECT
    COMMIT

This file also works for ip6tables-restore, so you may symlink it:

    ln -s /etc/iptables/iptables.rules /etc/iptables/ip6tables.rules

Then make sure Tor is running, and start iptables and ip6tables:

    systemctl {enable,start} tor iptables ip6tables

You may want to add `Requires=iptables.service` and `Requires=ip6tables.service` to whatever systemd unit logs your user in (most likely a display manager), to prevent any user processes from being started before the firewall up. See systemd.

## Troubleshooting

### Problem with user value

If the tor daemon failed to start, then run the following command as root (or use sudo)

    # tor

If you get the following error

    May 23 00:27:24.624 [warn] Error setting groups to gid 43: "Operation not permitted".
    May 23 00:27:24.624 [warn] If you set the "User" option, you must start Tor as root.
    May 23 00:27:24.624 [warn] Failed to parse/validate config: Problem with User value. See logs for details.
    May 23 00:27:24.624 [err] Reading config failed--see warnings above.

Then it means that the problem is with the User value, which likely means that one or more files or directories in your `/var/lib/tor` directory is not owned by tor. This can be determined by using the following find command:

    find /var/lib/tor/ ! -user tor

Any files or directories listed in the output from this command needs to have its ownership changed. This can be done individually for each file like so:

    chown tor:tor /var/lib/tor/filename

Or to change everything listed by the above find example, modify the command to this:

    find /var/lib/tor/ ! -user tor -exec chown tor:tor {} \;

Tor should now start up correctly.

Still if you cannot start the tor service, run the service using root (this will switch back to the tor user). To do this, change the user name in the `/etc/tor/torrc` file:

    User tor

Now modify the systemd's tor service file `/usr/lib/systemd/system/tor.service` as follows

    [Service]
    User=root
    Group=root
    Type=simple

The process will be run as tor user. For this purpose change user and group ID to tor and also make it writable:

    # chown -R tor:tor /var/lib/tor/
    # chmod -R 755 /var/lib/tor

Now save changes and run the daemon:

    # systemctl --system daemon-reload
    # systemctl start tor.service

### Daemon fails on restart

If after issuing a daemon restart you have log entries similar to

    Interrupt: we have stopped accepting new connections, and will shut down in 30 seconds. Interrupt again to exit now

and the daemon fails to start back up, a simple workaround is to open `/etc/rc.d/tor` in your favourite editor and increase the time waited between the shutting down and starting up again of the daemon. For example:

    /etc/rc.d/tor

        ;;
      restart)
        $0 stop
        sleep 35
        $0 start
        ;;

This will allow Tor to shutdown cleanly, and restart after a safe period of time. Remember that this file may be overwritten by upgrades.

## See also

- Running the Tor client on Linux/BSD/Unix
- Unix-based Tor Articles
- Software commonly integrated with Tor
- How to set up a Tor Hidden Service

Categories:

- Internet applications
- Proxy servers