Despite people generally considering the Tor network as an essential tool for anonymous browsing, german law enforcement agencies have managed to de-anonymize Tor users after putting surveillance on Tor servers for months.
Before we go into the what the agencies did, let’s take a look at some basics of Tor.
How Tor works
On a daily basis, millions of people use the Tor network to browse privately and visit websites on the dark web. Tor enhances privacy by directing internet traffic through a minimum of three randomly chosen routers, or nodes. During this process user data is encrypted before it reaches the destination via the exit node, ensuring a user’s activities and IP address remain confidential and secure.
Here’s a closer look at how this mechanism works:
- Entry node: When you start browsing with Tor, your connection is first directed to an entry node, also known as a guard node. This is where your internet traffic enters the Tor network, with your IP address only visible to this node.
- Middle nodes: After entering the Tor network, your traffic passes through one or more middle nodes. These nodes are randomly selected, and each one knows only the IP address of the previous relay and the next relay. This prevents any single relay from knowing the complete path of your internet activity.
- Exit node: The last relay in the chain is the exit node. It decrypts the information from the middle relays and sends it out to the destination. Importantly, the exit node strips away layers of encryption to communicate with the target server but does not know the origin of the traffic, ensuring that your IP address remains hidden.
This layered security model, like peeling an onion, is where Tor gets its name. Tor is an acronym for The Onion Router. Each layer ensures that none of the nodes in the path knows where the traffic came from and where it is going, significantly increasing the user’s anonymity and making it exceedingly difficult for anyone to trace the full path of the data.
Although many researchers theoretically considered that de-anonymization was possible, in general it was thought practically unfeasible if a user followed all the necessary security measures.
How did the de-anonymization work?
German news outlet NDR reports that law enforcement agencies got hold of data while performing server surveillance which was processed in such a way that it completely cancelled Tor anonymity. The reporters saw documents that showed four successful measures in just one investigation.
After following up on a post on Reddit and two years of investigation, the reporters came to the conclusion that Tor users can be de-anonymized by correlating the timing patterns of network traffic entering and exiting the Tor network, combined with broad and long-term monitoring of Tor nodes in data centers.
If you can monitor the traffic at both the entry and the exit points of the Tor network, you may be able to correlate the timing of a user’s true IP address to the destination of their traffic. To do this, one typically needs to control or observe both the entry node and the exit node used in a Tor circuit. This does not work when connecting to onion sites however, because the traffic would never leave the Tor network in such a case.
The timing analysis uses the size of the data packets that are exchanged to link them to a user. You can imagine that with access to a middle node, you can tie the incoming and outgoing data packets to one user. While this doesn’t reveal any of the content of the messages, this could help in establishing who’s communicating with who.
Tor is still safe, says Tor
The problem that Tor faces lies in the fact that it was designed with hundreds of thousands of different nodes all over the world in mind. In reality, there are about 7,000 to 8,000 active nodes, and many of them are in data centers. As a consequence, the “minimum of three” often means “only three” which increases the potential effectiveness of timing attacks.
The Tor Project said:
“The Tor Project has not been granted access to supporting documents and has not been able to independently verify if this claim is true, if the attack took place, how it was carried out, and who was involved.”
Based on the information provided, the Tor Project concluded that one user of the long-retired application Ricochet was de-anonymized through a guard discovery attack. This was possible, at the time, because the user was using a version of the software that neither had Vanguards-lite, nor the Vanguards add on, which were introduced to protect users from this type of attack
Which means they feel confident to claim that Tor is still safe to use. However, we would like to add that users should be aware that several law enforcement agencies–and cybercriminals–run Tor nodes, which can pose risks.
If you use Tor, here are some basic rules to stay as anonymous as possible:
- Always download Tor Browser from the official Tor Project website.
- Keep Tor Browser updated to the latest version for security patches.
- Use the default Tor Browser settings – don’t install add-ons or change the settings unless you know what you are doing and what the implications are.
- Enable the “Safest” security level in Tor Browser settings.
- Only visit HTTPS-encrypted websites.
- Avoid logging into personal accounts or entering personal information. If you post your personal information somewhere that undermines the whole idea of staying anonymous.
- Be extremely cautious about downloading files or clicking links, even more so on the Dark Web.
- Disable JavaScript if possible although this may break some sites.
- Clear cookies and local site data after each browsing session.
- Use a reputable VPN in addition to Tor for an extra layer of encryption.
- Run up-to-date antivirus/anti-malware software on your device.
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