Raspberry Pi as a Tor router and web filter
Activating IP Forwarding
The communication between the Wi-Fi subnet and Tor requires several adjustments of the network configuration. To begin, open the /etc/sysctl.conf file and append the directive net.ipv4.ip_forward=1 at the end. Then, activate the change by issuing sysctl -p.
The next step addresses the need for modifying the rules for iptables. You should first delete already existing rules using the commands iptables -F and iptables -t nat -F. You can then activate the new rules, which are shown in Listing 5, and immediately save them in the file /etc/iptables.ipv4.nat. Finally, open the /etc/network/interfaces file and append an empty line and the entry up iptables-restore /etc/iptables.ipv4.nat. This step instructs the system to process the rules on subsequent reboots.
Listing 5
Activating New Rules
# iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 22 -j REDIRECT --to-ports 22 # iptables -t nat -A PREROUTING -i wlan0 -p udp --dport 53 -j REDIRECT --to-ports 53 # iptables -t nat -A PREROUTING -i wlan0 -p tcp --syn -j REDIRECT --to-ports 9040 # iptables-save > /etc/iptables.ipv4.nat
Installing Tor
The /etc/tor/torrc file contains the Tor configuration information. Directly following the line ##https://www.torproject.org/docs/faq#torrc, add the text from Listing 6. You should also create a log file (Listing 7) so that Tor has a place to record its messages. Finally, you can start Tor by invoking service tor start. By issuing the command update-rc.d tor enable, you ensure that this service also starts up automatically after a reboot.
Listing 6
Configuring /etc/tor/torrc
Log notice file /var/log/tor/notices.log VirtualAddrNetwork 10.192.0.0/10 AutomapHostsSuffixes .onion,.exit AutomapHostsOnResolve 1 TransPort 9040 TransListenAddress 192.168.42.1 DNSPort 53 DNSListenAddress 192.168.42.1
Listing 7
Creating a Log File
# touch /var/log/tor/notices.log # chown debian-tor /var/log/tor/notices.log # chmod 644 /var/log/tor/notices.log
To use Tor from now on, you just need to register the device of your choice with the new Wi-Fi network. You can check whether this arrangement works as intended by calling up the web page https://check.torproject.org. In case of success, you will see the message Congratulations. Your browser is configured to use Tor (Figure 4).
Figure 4: The website check.torproject.org checks whether your system is properly connected to the Tor network..
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