The Tor network is designed to protect users' privacy by routing their internet traffic through a series of relays, making it difficult to trace their online activities. However, the network faces various threats, even from people who just use a Tor client. These client-side attackers, while limited in their capabilities compared to more sophisticated attackers, can still pose significant risks to the network's performance and reliability.

A Tor client is software that lets you use the Tor network. The most common Tor client is the Tor Browser, which is similar to a regular web browser but with built-in privacy protections.

Understanding Client-side Adversaries

Client-side attackers are individuals or entities that use a Tor client to carry out attacks on the network. Unlike more advanced attackers, they do not control any relays or infrastructure within the Tor network. Instead, they rely on their access to the internet and a Tor client to execute their attacks.

Denial of Service (DoS) attacks

One of the primary threats posed by client-side attackers is the ability to perform a Denial of Service (DoS) attack.

A Denial of Service (DoS) attack is a tactic where an attacker attempts to make a service, in this case, the Tor network, hard to use for its intended users. Client-side attackers can execute DoS attacks to degrade the performance of the Tor network, causing disruptions that impact all users.

They could flood the network with an overwhelming amount of traffic using external services, or exploiting the Tor protocol itself. This traffic might not necessarily come from a single client but could be distributed across many clients in a coordinated attack. The result is a significantly slowed network, making it difficult for legitimate users to connect or use Tor effectively. This disruption can also frustrate relay operators, sometimes leading them to shut down their relays, which inadvertently weakens the network—a potential goal of the attacker.