The Onion Routing (Tor)

Tor is a network that offers anonymization services without requiring users to understand the underlying technical principles in order to use it. The technical details are not the focus of this article; rather, it focuses on its use and the reasons for using it (without claiming to be exhaustive). “Onion Routing” (or “router”) was originally used as an acronym (TOR), but that no longer matters today—though it still accurately describes the process. Many people have surely come across the term “darknet.” It describes how websites and services can be operated anonymously within the Tor network. However, that could be the subject of a separate article and is not the focus here; it does not concern the average user.

Function

Even though the Tor network can certainly anonymize many services, it is primarily used in the browser. “Onion” is the English word for “Zwiebel” (onion), and that aptly describes how a request from your Tor browser is handled on its way to the website. Let’s first consider a normal connection without Tor, such as the one established by the default browser in any operating system. Whether the server initiates the connection via HSTS or the browser triggers an automatic redirect, most connections today are encrypted using SSL (HTTPS). So why would using Tor be necessary? To conceal who is communicating with whom—the so-called metadata and tracking are thereby made more difficult, or even impossible if you follow a few rules.

To do this, the Tor Browser first connects to an entry or bridge server and establishes an encrypted connection. Through this connection, it sends its request along with the address the Tor Browser wishes to display. The server encrypts the request—including the sender’s address—and forwards it via an encrypted connection to a relay server, which now knows only the first server as the sender and the requested address. The Tor Browser does not know which relay is used; the entry server makes that selection. This process can now be repeated several times. This creates the “onion” structure, as each participating server adds a new layer of encryption. In this process, each server knows only its predecessor and successor and can only encrypt or decrypt these two connections. The last server in the chain is the exit node, which forwards the request to the originally intended address.

Let’s now look at what an eavesdropper can find out this way. Between the relays, you can only see which servers are communicating with each other. At the beginning, you can see that you are communicating with a server whose function is, at best, unknown—or that it belongs to the Tor network. Since all connections are encrypted, no one outside the Tor network can determine who you’re trying to contact or what you’ve asked. Only the exit node sends your request to the server you originally intended to reach—though it’s encrypted if the connection is handled via HTTPS (as is the case with a standard browser)—so an eavesdropper can only see that a Tor exit node is communicating with a web server. Even if someone were able to monitor the entire Internet in real time, since all Tor servers constantly communicate with each other in a random, crisscross pattern, no connection can be traced back.

The return path now follows naturally. The server in question responds to the originating node with the requested website. The originating node sends this back to the last relay, encrypted along with the request (the onion). The relay decrypts the website and removes one layer of the onion. This gives it the address of the next relay (or entry server), and it sends the newly encrypted packets to that relay. This process continues until the onion, now completely stripped of all layers, arrives back at the entry server, which then delivers the website to you via the encrypted connection. None of the relays knows the source, and not even the web server learns who requested the website.

Reasons

There are countless reasons why someone might need or want this anonymity. I mentioned one at the beginning: it prevents tracking by advertising networks. But what seems most important to me is the ability to hide connections. A whistleblower certainly doesn’t want to be exposed because of a leak (a prominent example: Edward Snowden). Activists in Hong Kong, China, or North Korea also have good reasons to conceal who they’re talking to. And every user who routes less important requests through the Tor network contributes to the background noise in which activists can hide.

There’s also an important distinction I haven’t addressed yet. There are two types of entry points into the Tor network. The publicly known entry servers provide easy access for everyone in free countries. The Tor Browser can automatically connect to the network through them. However, in an environment where all communication is monitored, connections to these known servers can be blocked. That’s where bridges come in. They are known exclusively within the Tor network, and users can only obtain an address by sending a request to the network. These requests are limited, and addresses are issued in a controlled manner, making it much more difficult to compile lists of bridges in order to block them.

Support

How can you support this? First of all, download, install, and use the Tor Browser regularly. You can use it exclusively for yourself or share it as a P2P server, thereby acting as a relay for other connections (you can also act as an exit node, but you shouldn’t do that from home). Donations are also welcome; they help the project run its own servers, for example. You can donate via credit card or PayPal, either as a one-time donation or on a regular basis. Depending on the amount, you might receive a gift in return, though you can choose to forgo it in support of the Tor Project.

If you have a spare computer that’s always running, you can also install a server on it, or allocate unused resources on a dedicated web server for this purpose. To do so, however, you’ll need to delve much deeper into the subject. Your first point of contact should be the Zwiebelfreunde e.V. association, which also runs the Torservers.net project.

The Tor Browser is available for all major operating systems. For those who absolutely need it, I’d like to recommend a special solution that Edward Snowden also prefers: Tails. This is a portable operating system. Installed on a USB drive, it’s the safest and most comprehensive solution. Every time you restart, it resets to its original state—no browsing history, no cookies, and viruses, worms, and even the NSA don’t stand a chance.