Now that we have a Tor bridge running (previous guide), we might want to obfuscate the traffic to look more like normal HTTPS traffic. This is useful for censorship circumvention or if you simply don’t want “spies” knowing that you are using Tor.
This guide assumes you are running Debian or Ubuntu but you can adapt what you learn here to use in other distros.
This guide also assumes you read my previous guide on how to set up a Tor bridge!
Installing and setting up obfs4proxy
To be able to obfuscate the traffic, we are going to install obfs4 proxy which is as the name says, a proxy server using the obfs4 protocol.
sudo apt install obfs4proxy
Now we’re going to edit
/etc/tor/torrc and add the following lines:
ServerTransportPlugin obfs4 exec /usr/bin/obfs4proxy ServerTransportListenAddr obfs4 0.0.0.0:443 ExtORPort auto
While 443 is the recommended port, it might already be in use for HTTPS in which case you should use another common port like one used for encrypted email transfer. Note that using any port below 1024 will need further setup due to security restrictions.
Allowing ports below 1024
As stated above, using any port below 1024 will need further setup. First run the following command:
sudo setcap cap_net_bind_service=+ep /usr/bin/obfs4proxy
Now edit the files
/lib/systemd/system/[email protected] and
/lib/systemd/system/[email protected] and in both files change
NoNewPrivileges=no and then execute
systemctl daemon-reload to apply the changes.
It can happen, that during an update, the Tor service files will be overwritten and the modifications thus removed. This will result in the proxy not functioning on the desired port anymore (if below 1024). This can be fixed by marking the service files as immutable after modification, like this:
sudo chattr +i /lib/systemd/system/[email protected] sudo chattr +i /lib/systemd/system/[email protected]
Restarting Tor and testing
Now simply restart Tor with
systemctl restart tor and wait for it to start up. Running
netstat -tlpn will show if obfs4proxy is up and running at the desired port. Remember to allow the desired obfs4proxy port in your firewall!
Using the bridge
To use the bridge you need to know your bridge line which is formatted like the following:
Bridge obfs4 IP:PORT FINGERPRINT cert=CERTIFICATE iat-mode=0
To get the fingerprint, as discussed in my previous guide, simply run
cat /var/lib/tor/fingerprint and use the hexadecimal encoded fingerprint at the end of the line. To get the certificate and overall bridge line, run
cat /var/lib/tor/pt_state/obfs4_bridgeline.txt which will output the line you will have to copy and edit to replace IP address, port and fingerprint.
Your final bridge line to use in Tor Browser might look like:
Bridge obfs4 18.104.22.168:443 0F00ABC123 cert=raNdomStufFinbAse64+/fOobAR iat-mode=0
In Tor Browser, update the bridge line we used in my previous guide, with the new line. Make sure the line really does start with “Bridge obfs4” or it won’t work!
It’s easy to extend our Tor bridge to add obfuscation which is recommended so that spying eyes won’t know you are using Tor, which can help to circumvent censorship or simply not get attention. ;)
Check my previous guide to see how to set all of this up from scratch