Since mid-2022, the privacy-preserving Tor Network has been plagued by denial-of-service attacks, making the network slow and – at times – completely unusable.
In its latest software release, Tor is aiming to “defend” itself against these attacks using PoW, which features the same encryption mechanism that underpins and secures Bitcoin. Using PoW in some way to prevent attacks has been an idea in the Tor community for many years. Now it’s finally on track.
The goal of this implementation is to require attackers to use more computational resources to carry out their attacks.
Tor is a network that privatizes the IP addresses of its users. It is also used by Bitcoin and other cryptocurrency advocates to improve their privacy, such as hiding the IP addresses of Bitcoin nodes or transaction destinations.
Although Bitcoin and Tor currently both use PoW, the technology of the same name, the implementation of the private network is quite different because the developers created it specifically to protect against attacks on Tor.
There are algorithmic similarities, but there are some important differences. Tor’s PoW system is dynamic: instead of forcing clients to pursue a static goal, we ask clients to ‘bid’ using their PoW efforts.
Onion services are websites or services that run on Tor, protecting the website’s IP address. The network’s algorithms can detect when a website is receiving a lot of traffic at once – for example, from an attacker. When that happens, PoW kicks in, requiring users to put in more computational effort to access the website.
Normal users won’t notice this change, but attackers will, as they will have to use more computation to get the same effect.